Influenza Vaccine Effectiveness Against Influenza-Associated Hospitalizations and Emergency Department or Urgent Care Encounters Among Children and Adults—VISION, United States, 2024–2025 Season

Jennifer DeCuir; Emily L Reeves; Zachary A Weber; Duck-Hye Yang; Stephanie A Irving; Sara Y Tartof; Nicola P Klein; Shaun J Grannis; Toan C Ong; Sarah W Ball; Malini B DeSilva; Kristin Dascomb; Allison L Naleway; Padma Koppolu; S Bianca Salas; Lina S Sy; Bruno Lewin; Richard Contreras; Ousseny Zerbo; John R Hansen; Lawrence Block; Karen B Jacobson; Brian E Dixon; Colin Rogerson; Thomas Duszynski; William F Fadel; Michelle A Barron; David Mayer; Catia Chavez; Adam Yates; Lindsey Kirshner; Charlene E McEvoy; Omobosola O Akinsete; Inih J Essien; Tamara Sheffield; Daniel Bride; Julie Arndorfer; Josh Van Otterloo; Karthik Natarajan; Caitlin S Ray; Amanda B Payne; Katherine Adams; Brendan Flannery; Shikha Garg

doi:10.1093/ofid/ofag473

. 2026 Aug 4;13(8):ofag473. doi: 10.1093/ofid/ofag473

Influenza Vaccine Effectiveness Against Influenza-Associated Hospitalizations and Emergency Department or Urgent Care Encounters Among Children and Adults—VISION, United States, 2024–2025 Season

Jennifer DeCuir ^1,^✉,², Emily L Reeves ², Zachary A Weber ³, Duck-Hye Yang ⁴, Stephanie A Irving ⁵, Sara Y Tartof ^6,⁷, Nicola P Klein ⁸, Shaun J Grannis ^9,¹⁰, Toan C Ong ¹¹, Sarah W Ball ¹², Malini B DeSilva ¹³, Kristin Dascomb ¹⁴, Allison L Naleway ¹⁵, Padma Koppolu ¹⁶, S Bianca Salas ¹⁷, Lina S Sy ¹⁸, Bruno Lewin ^19,²⁰, Richard Contreras ²¹, Ousseny Zerbo ²², John R Hansen ²³, Lawrence Block ²⁴, Karen B Jacobson ²⁵, Brian E Dixon ^26,²⁷, Colin Rogerson ^28,²⁹, Thomas Duszynski ^30,³¹, William F Fadel ^32,³³, Michelle A Barron ³⁴, David Mayer ³⁵, Catia Chavez ³⁶, Adam Yates ³⁷, Lindsey Kirshner ³⁸, Charlene E McEvoy ^39,⁴⁰, Omobosola O Akinsete ^41,⁴², Inih J Essien ⁴³, Tamara Sheffield ^44,⁴⁵, Daniel Bride ^46,⁴⁷, Julie Arndorfer ⁴⁸, Josh Van Otterloo ⁴⁹, Karthik Natarajan ^50,⁵¹, Caitlin S Ray ⁵², Amanda B Payne ⁵³, Katherine Adams ⁵⁴, Brendan Flannery ⁵⁵, Shikha Garg ^56,^✉,²

¹ National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

² National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

³Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA

⁴Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA

⁵ Kaiser Permanente Center for Health Research, Portland, Oregon, USA

⁶ Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA

⁷ Kaiser Permanente Bernard J Tyson School of Medicine, Pasadena, California, USA

⁸ Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA

⁹ Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA

¹⁰ School of Medicine, Indiana University, Indianapolis, Indiana, USA

¹¹ School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA

¹²Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA

¹³Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA

¹⁴ Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA

¹⁵ Kaiser Permanente Center for Health Research, Portland, Oregon, USA

¹⁶ Kaiser Permanente Center for Health Research, Portland, Oregon, USA

¹⁷ Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA

¹⁸ Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA

¹⁹ Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA

²⁰ Kaiser Permanente Bernard J Tyson School of Medicine, Pasadena, California, USA

²¹ Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA

²² Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA

²³ Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA

²⁴ Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA

²⁵ Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA

²⁶ Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA

²⁷ Fairbanks School of Public Health, Indiana University Indianapolis, Indianapolis, Indiana, USA

²⁸ Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA

²⁹ School of Medicine, Indiana University, Indianapolis, Indiana, USA

³⁰ Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA

³¹ Fairbanks School of Public Health, Indiana University Indianapolis, Indianapolis, Indiana, USA

³² Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA

³³ Fairbanks School of Public Health, Indiana University Indianapolis, Indianapolis, Indiana, USA

³⁴ School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA

³⁵ School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA

³⁶ School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA

³⁷Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA

³⁸Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA

³⁹Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA

⁴⁰Pulmonary, Critical Care and Sleep Department, HealthPartners Institute, Minneapolis, Minnesota, USA

⁴¹Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA

⁴²Infectious Disease Department, HealthPartners Institute, Minneapolis, Minnesota, USA

⁴³Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA

⁴⁴ Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA

⁴⁵ Immunization Programs, Intermountain Health, Salt Lake City, Utah, USA

⁴⁶ Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA

⁴⁷ Enterprise Analytics, Intermountain Health, Salt Lake City, Utah, USA

⁴⁸ Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA

⁴⁹ Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA

⁵⁰ Department of Biomedical Informatics, Columbia University Irving Medical Center, New York, New York, USA

⁵¹ Medical Informatics Services, New York-Presbyterian Hospital, New York, New York, USA

⁵² National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

⁵³ National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

⁵⁴ National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

⁵⁵ National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

⁵⁶ National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

^✉

Correspondence: Jennifer DeCuir, MD, PhD, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30329-4027 (qeo3@cdc.gov); Shikha Garg, MD, MPH, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30329-4027 (izj7@cdc.gov).

Potential conflicts of interest. All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. During the conduct of the study, all Kaiser Permanente Southern California Department of Research and Evaluation and Kaiser Permanente Northern California Division of Research-affiliated authors reported receiving contractual support from the Centers for Disease Control and Prevention (CDC) via payments made to their respective institutions. Additionally, all authors affiliated with Columbia University, HealthPartners Institute, Intermountain Health, Kaiser Permanente Center for Health Research, Regenstrief Institute, and University of Colorado Anschutz Medical Campus reported receiving contractual support from the CDC during the conduct of the study, via subcontracts from Westat, Inc. with payments made to their respective institutions. Unrelated to the submitted work, the following disclosures were reported from the past 36 months: SYT reports a contract from Pfizer. NPK reports support from Pfizer for a COVID-19 vaccine clinical trial and research support from Sanofi Pasteur, Merck, Pfizer, Moderna, Janssen, AstraZeneca, Seqirus, and GlaxoSmithKline. SJG reports contracts with National Institutes of Health (NIH) National Center for Advancing Translational Sciences and NIH National Institute of Mental Health. TCO received consulting fees from Regenstrief Institute and support for travel from Patient-Centered Outcomes Research Institute (PCORI) and Regenstrief Institute and has a current patent, PCT/US2018/047961. MBD reports grants from the Centers for Disease Control and Prevention (CDC) for the Vaccine Safety Datalink and Centers for Excellence in Newcomer Health. LSS reports contracts with GlaxoSmithKline, Moderna, Dynavax, and AstraZeneca. OZ reports grant number R01AI168373 with the National Institute of Allergy and Infectious Diseases and contracts with Moderna, Pfizer, and NIH. KBJ reports research support from Pfizer. BED reports a contract with Vaccine Safety Datalink Project, Contract No. 75D30122D15424. WFF reports a contract with Vaccine Safety Datalink Project, Contract No. 75D30122D15424. MAB was a speaker bureau participant—Innoviva Specialty Therapeutics—Oct 2023. AY reports a contract with the University of Utah and Novavax. CEM reports support from NIH, Department of Defense, PCORI, AstraZeneca, and GlaxoSmithKline, was a Pri-Med lecturer, and is a member of the American Lung Association of Minnesota Board, Minnesota Department of Health Long COVID Advisory Committee, and Minnesota Department of Health Asthma Care Advisory Committee. TS is a member of the CDC Advisory Committee on Immunization Practices Influenza Vaccine Work Group, chair of Utah Adult Immunization Coalition vaccine quality improvement and advocacy group, and a member of Utah Department of Health and Human Services Scientific Advisory Committee on Vaccines. KN reports support from NIH National Cancer Institute (NCI), National Heart, Lung, and Blood Institute (NHLBI), and Office of the Director. No other disclosures were reported.

PMCID: PMC13481979 PMID: 42614619

Abstract

Background

The 2024–2025 influenza season was the most severe in the United States (US) since 2017–2018, with co-circulation of both influenza A virus subtypes (H1N1 and H3N2). Influenza vaccine effectiveness (VE) has varied by season, setting, and patient characteristics.

Methods

Using electronic healthcare encounter data from 7 VISION sites in 8 US states, we evaluated influenza VE against influenza-associated hospitalizations and emergency department or urgent care (ED/UC) encounters from October 2024 to April 2025 among children aged 6 months–17 years and adults aged ≥18 years. Using a test-negative, case-control design, we compared the odds of influenza vaccination between acute respiratory illness encounters with a positive (cases) versus negative (controls) test for influenza by molecular assay, adjusting for confounders.

Results

Analyses included 108 618 encounters (5764 hospitalizations and 102 854 ED/UC encounters) among children and 309 483 encounters (76 072 hospitalizations and 233 411 ED/UC encounters) among adults. Among children across care settings, 17.0% (6097/35 765) of cases versus 29.4% (21 449/72 853) of controls were vaccinated. Among adults, 28.2% (21 832/77 477) of cases versus 44.2% (102 560/232 006) of controls were vaccinated. VE was 51% (95% confidence interval [95% CI]: 41%–60%) against influenza-associated hospitalizations and 54% (95% CI: 52%–55%) against influenza-associated ED/UC encounters among children. VE was 43% (95% CI: 41%–46%) against influenza-associated hospitalizations and 49% (95% CI: 47%–50%) against influenza-associated ED/UC encounters among adults.

Conclusions

Influenza vaccination provided protection against influenza-associated hospitalizations and ED/UC encounters among children and adults in the US during the severe 2024–2025 influenza season. These findings support influenza vaccination as an important tool to reduce influenza.

Keywords: case-control studies, influenza, test-negative design, vaccination, vaccine effectiveness

During the 2024–2025 influenza season, influenza vaccination provided protection against influenza-associated hospitalizations (43%–51%) and emergency department or urgent care encounters (49%–54%) among children and adults in the United States.

The 2024–2025 influenza season was the first high-severity season in the United States (US) since 2017–2018, with high-severity indicators observed in all age groups [1]. Over the course of the season, there were an estimated 23 million medical encounters, 710 000 hospitalizations, and 45 000 deaths due to influenza, with the highest hospitalization rates occurring among adults aged ≥65 years [1, 2]. Influenza A viruses predominated, with co-circulation of A(H1N1)pdm09 and A(H3N2) viruses [3]. Although studies have shown that reference strains used for the 2024–2025 Northern Hemisphere influenza vaccines were antigenically similar to circulating A(H1N1)pdm09 and B/Victoria viruses, some antigenic differences were identified between the 2024–2025 vaccine strains and circulating A(H3N2) viruses [3].

Influenza vaccination was recommended for all persons aged ≥6 months in the US during the 2024–2025 season [4]. Influenza vaccination has been shown to provide protection against a variety of influenza-associated outcomes, including symptomatic illness, outpatient visits, hospitalizations, and severe disease [5–8]; however, vaccine effectiveness (VE) may vary by season due to patient characteristics, antigenic similarity between vaccine and circulating influenza viruses, and other factors. Annual estimates from established VE platforms are important to assess the US influenza vaccination program [9].

We estimated the effectiveness of 2024–2025 seasonal influenza vaccines against influenza-associated hospitalizations and emergency department (ED) or urgent care (UC) encounters among US children and adults.

METHODS

Population and Study Design

This analysis was conducted using data from the VIrtual SARS-CoV-2, Influenza, and Other respiratory viruses Network (VISION), a research collaboration between the US Centers for Disease Control and Prevention (CDC) and healthcare systems with integrated clinical, laboratory, and immunization records [10]. Detailed VISION methods have been published previously [11]. Briefly, participating healthcare systems capture electronic health record (EHR) data on medical encounters for acute respiratory illness (ARI) to evaluate the effectiveness of vaccines against influenza and other respiratory viruses using a test-negative, case-control design.

The current analysis included ARI-associated encounters occurring in the hospital and ED/UC settings from 7 VISION sites in 8 US states: Kaiser Permanente Northern California (California), Kaiser Permanente Southern California (California), University of Colorado (Colorado), Regenstrief Institute (Indiana), HealthPartners (Minnesota and Wisconsin), Kaiser Permanente Center for Health Research (Oregon and Washington), and Intermountain Health (Utah). ARI was defined using International Classification of Diseases, Tenth Revision (ICD-10) codes. Eligible encounters were those with ≥1 ARI-associated ICD-10 discharge diagnosis code and a molecular influenza test result among patients aged ≥6 months (Supplementary Table 1). Encounters were included from the date of the first influenza-positive case on or after 1 October 2024 by site and setting to the date of the last influenza-positive case on or before 30 April 2025 by site and setting (Supplementary Table 2). The same patient could contribute >1 encounter to the analysis. Emergency department and/or UC encounters occurring within 7 days in the same patient were combined into a single ED/UC encounter. Hospitalizations occurring within 30 days in the same patient were combined into a single hospitalization.

Patient demographic and clinical characteristics were extracted from EHRs, including data on underlying medical conditions and critical illness outcomes. Underlying medical conditions were ascertained for hospitalizations using ICD-10 discharge diagnosis codes from the hospital encounter (Supplementary Table 3). Underlying medical conditions are not reported for ED/UC encounters due to potential under-capture in these settings. Cases were defined as ARI-associated encounters with a positive molecular influenza test result from 10 days before to 72 hours after the encounter date. Controls were defined as ARI-associated encounters with a negative molecular influenza test result during the same window. Influenza vaccination status was determined from EHRs, state and local immunization information systems, and/or claims data. Data on vaccine product type were collected when available. Vaccinated encounters were defined as those with receipt of ≥1 dose of influenza vaccine on or after 1 August 2024 and ≥14 days before the index date (defined as the earlier date of either the most recent influenza test or the encounter date). Unvaccinated encounters had no documented receipt of influenza vaccine on or after 1 August 2024 and ≥14 days before the index date.

Encounters with missing or indeterminate results from a molecular influenza test, influenza vaccination <14 days before the index date, or a clinical diagnosis of influenza without a confirmatory test were excluded. Encounters with a positive molecular SARS-CoV-2 test result from 10 days before to 72 hours after the encounter date or a clinical diagnosis of COVID-19 were also excluded to reduce potential bias in VE estimates due to correlation between influenza and COVID-19 vaccination behaviors [12, 13].

Statistical Analysis

Statistical analyses were conducted separately by age group and encounter setting (pediatric hospitalizations, pediatric ED/UC encounters, adult hospitalizations, adult ED/UC encounters). Demographic and clinical characteristics for each group were described by case and vaccination status, with a standardized mean difference of >0.20 between groups considered meaningful. VE was estimated using multivariable logistic regression comparing the odds of influenza vaccination among influenza-positive cases and influenza-negative controls. VE models were adjusted for age, sex, race and ethnicity, site, and calendar time. Age and calendar time were modeled as natural cubic splines with 4 degrees of freedom. VE was calculated as (1 − adjusted odds ratio) × 100 expressed as a percent.

VE estimates were stratified by time since vaccination (14–59, 60–119, ≥120 days), influenza type (A, B), and age group (6 months–4 years, 5–17 years, 18–49 years, 50–64 years, ≥65 years). Among pediatric and adult hospitalizations, VE estimates were also stratified by the presence of ≥1 immunocompromising condition (immunocompetent, immunocompromised), and VE was estimated against intensive care unit (ICU) admission and in-hospital death. VE against influenza-associated ICU admission was estimated by comparing the odds of influenza vaccination among influenza-positive cases who were admitted to an ICU and had no in-hospital death versus all influenza-negative hospitalized controls. VE against influenza-associated in-hospital death was estimated by comparing the odds of influenza vaccination among influenza-positive cases who had in-hospital death versus all influenza-negative hospitalized controls. Among pediatric and adult ED/UC encounters, VE estimates were further stratified by setting (ED only, UC only).

Analyses were conducted in SAS version 9.4 (SAS Institute, Inc.) or R version 4.1.0 (R Foundation for Statistical Computing). This activity was reviewed by CDC, deemed not research or research not involving human subjects, and was conducted consistent with applicable federal law and CDC policy (see eg, 45C.F.R. part 46, 21C.F.R. part 56; 42 U.S.C. §241(d); 5 U.S.C. §552a; 44 U.S.C. §3501 et seq). Patient informed consent was not required.

RESULTS

Included Population

A total of 90 700 ARI-associated hospitalizations and 367 065 ARI-associated ED/UC encounters were identified. After excluding 8864 (9.8%) hospitalizations and 30 800 (8.4%) ED/UC encounters (Supplementary Figure 1), 81 836 (90.2%) hospitalizations and 336 265 (91.6%) ED/UC encounters were included. Among 81 836 ARI-associated hospitalizations, 4169 (5.1%) individuals had >1 encounter during the study period. Among 336 265 ARI-associated ED/UC encounters, 19 820 (5.9%) patients had >1 ED/UC encounter.

Influenza Circulation

Across sites, influenza activity peaked in early February (Supplementary Figures 2A-2D). Of 113 242 influenza cases, 101 489 (89.6%) were influenza A, 11 618 (10.3%) were influenza B, and 135 (0.1%) tested positive for >1 influenza virus. The proportion of influenza B cases was higher in children (15.9% of cases) than in adults (7.6% of cases).

Pediatric Patient Characteristics

Of 5764 ARI-associated hospitalizations in children, 825 (14.3%) were influenza-positive cases and 4939 (85.7%) were influenza-negative controls (Table 1). Influenza positivity among ARI-associated hospitalizations included in this analysis was 10.4% among children aged 6 months–4 years and 19.1% among those aged 5–17 years. Overall, 1978 (34.3%) hospitalized children had received an influenza vaccine before their encounter (22.4% of cases versus 36.3% of controls, Figure 1). Among those vaccinated, median time since vaccination was 98 days. A total of 818 (14.2%) hospitalized children were admitted to an ICU during their admission, and 30 (0.5%) died.

Table 1.

Characteristics of Acute Respiratory Illness-Associated Hospitalizations and Emergency Department/Urgent Care Encounters Among Children Aged 6 Months–17 Years by Influenza Vaccination and Test Status—VISION, October 2024–April 2025

		Influenza Vaccination Status			Influenza Test Result
	Total (col %)	Vaccinated (row %)	Unvaccinated (row %)	SMD^a	Positive (row %)	Negative (row %)	SMD^a
All hospitalizations	5764	1978 (34.3)	3786 (65.7)		825 (14.3)	4939 (85.7)
Influenza vaccination status
Unvaccinated	3786 (65.7)	0 (0.0)	3786 (100.0)	–	640 (16.9)	3146 (83.1)	0.308
Vaccinated	1978 (34.3)	1978 (100.0)	0 (0.0)		185 (9.4)	1793 (90.6)
14–59 days earlier	519 (9.0)	519 (100.0)	0 (0.0)		34 (6.6)	485 (93.4)
60–119 days earlier	723 (12.5)	723 (100.0)	0 (0.0)		85 (11.8)	638 (88.2)
≥120 days earlier	736 (12.8)	736 (100.0)	0 (0.0)		66 (9.0)	670 (91.0)
Month of encounter
October 2024	346 (6.0)	63 (18.2)	283 (81.8)	0.289	4 (1.2)	342 (98.8)	0.745
November 2024	637 (11.1)	165 (25.9)	472 (74.1)		24 (3.8)	613 (96.2)
December 2024	962 (16.7)	295 (30.7)	667 (69.3)		169 (17.6)	793 (82.4)
January 2025	991 (17.2)	339 (34.2)	652 (65.8)		242 (24.4)	749 (75.6)
February 2025	1193 (20.7)	450 (37.7)	743 (62.3)		253 (21.2)	940 (78.8)
March 2025	955 (16.6)	392 (41.0)	563 (59.0)		94 (9.8)	861 (90.2)
April 2025	680 (11.8)	274 (40.3)	406 (59.7)		39 (5.7)	641 (94.3)
Site
Site A	113 (2.0)	39 (34.5)	74 (65.5)	0.216	8 (7.1)	105 (92.9)	0.180
Site B	21 (0.4)	6 (28.6)	15 (71.4)		3 (14.3)	18 (85.7)
Site C	2133 (37.0)	703 (33.0)	1430 (67.0)		264 (12.4)	1869 (87.6)
Site D	257 (4.5)	86 (33.5)	171 (66.5)		35 (13.6)	222 (86.4)
Site E	901 (15.6)	229 (25.4)	672 (74.6)		137 (15.2)	764 (84.8)
Site F	1085 (18.8)	415 (38.2)	670 (61.8)		191 (17.6)	894 (82.4)
Site G	1254 (21.8)	500 (39.9)	754 (60.1)		187 (14.9)	1067 (85.1)
Median age (IQR), years	4 (1.8, 8)	3 (1.4, 7)	4 (2, 9)		6 (2, 10)	3 (1.6, 8)
Age group
6 months–4 years	3167 (54.9)	1220 (38.5)	1947 (61.5)	0.208	330 (10.4)	2837 (89.6)	0.354
5–17 years	2597 (45.1)	758 (29.2)	1839 (70.8)		495 (19.1)	2102 (80.9)
Female	2596 (45.0)	883 (34.0)	1713 (66.0)	0.012	378 (14.6)	2218 (85.4)	0.018
Race/ethnicity
Black Non-Hispanic	425 (7.4)	118 (27.8)	307 (72.2)	0.196	78 (18.4)	347 (81.6)	0.135
Hispanic	1689 (29.3)	564 (33.4)	1125 (66.6)		264 (15.6)	1425 (84.4)
Other Non-Hispanic^b	710 (12.3)	325 (45.8)	385 (54.2)		102 (14.4)	608 (85.6)
Unknown	306 (5.3)	100 (32.7)	206 (67.3)		45 (14.7)	261 (85.3)
White Non-Hispanic	2634 (45.7)	871 (33.1)	1763 (66.9)		336 (12.8)	2298 (87.2)
Any underlying medical condition^c	3625 (62.9)	1336 (36.9)	2289 (63.1)	0.148	491 (13.5)	3134 (86.5)	0.081
Respiratory condition	2666 (46.3)	996 (37.4)	1670 (62.6)	0.125	298 (11.2)	2368 (88.8)	0.241
Non-respiratory condition	1829 (31.7)	735 (40.2)	1094 (59.8)	0.176	308 (16.8)	1521 (83.2)	0.138
Immunocompromising condition^d	321 (5.6)	151 (47.0)	170 (53.0)	0.132	59 (18.4)	262 (81.6)	0.076
Influenza type
Influenza A only	732 (88.7)	167 (22.8)	565 (77.2)	0.082	732 (100.0)	0 (0.0)	–
Influenza B only	92 (11.2)	18 (19.6)	74 (80.4)		92 (100.0)	0 (0.0)
Influenza A and B	1 (0.1)	0 (0.0)	1 (100.0)		1 (100.0)	0 (0.0)
ICU admission
Yes	818 (14.2)	302 (36.9)	516 (63.1)	0.048	120 (14.7)	698 (85.3)	0.032
No	4866 (84.4)	1647 (33.8)	3219 (66.2)		691 (14.2)	4175 (85.8)
Unknown	80 (1.4)	29 (36.2)	51 (63.7)		14 (17.5)	66 (82.5)
In-hospital death
Yes	30 (0.5)	9 (30.0)	21 (70.0)	0.014	8 (26.7)	22 (73.3)	0.063
No	5734 (99.5)	1969 (34.3)	3765 (65.7)		817 (14.2)	4917 (85.8)
Unknown	0 (0.0)	0 (0.0)	0 (0.0)		0 (0.0)	0 (0.0)
All ED/UC encounters	102 854	25 568 (24.9)	77 286 (75.1)		34 940 (34.0)	67 914 (66.0)
Influenza vaccination status
Unvaccinated	77 286 (75.1)	0 (0.0)	77 286 (100.0)	–	29 028 (37.6)	48 258 (62.4)	0.289
Vaccinated	25 568 (24.9)	25 568 (100.0)	0 (0.0)		5912 (23.1)	19 656 (76.9)
14–59 days earlier	6670 (6.5)	6670 (100.0)	0 (0.0)		1105 (16.6)	5565 (83.4)
60–119 days earlier	10 217 (9.9)	10 217 (100.0)	0 (0.0)		2810 (27.5)	7407 (72.5)
≥120 days earlier	8681 (8.4)	8681 (100.0)	0 (0.0)		1997 (23.0)	6684 (77.0)
Month of encounter
October 2024	7594 (7.4)	716 (9.4)	6878 (90.6)	0.341	174 (2.3)	7420 (97.7)	0.841
November 2024	10 017 (9.7)	1984 (19.8)	8033 (80.2)		988 (9.9)	9029 (90.1)
December 2024	20 065 (19.5)	4482 (22.3)	15 583 (77.7)		7996 (39.9)	12 069 (60.1)
January 2025	20 903 (20.3)	5098 (24.4)	15 805 (75.6)		10 592 (50.7)	10 311 (49.3)
February 2025	20 896 (20.3)	5711 (27.3)	15 185 (72.7)		9992 (47.8)	10 904 (52.2)
March 2025	14 127 (13.7)	4409 (31.2)	9718 (68.8)		3841 (27.2)	10 286 (72.8)
April 2025	9252 (9.0)	3168 (34.2)	6084 (65.8)		1357 (14.7)	7895 (85.3)
Site
Site A	2695 (2.6)	654 (24.3)	2041 (75.7)	0.251	1023 (38.0)	1672 (62.0)	0.164
Site B	5756 (5.6)	1498 (26.0)	4258 (74.0)		2120 (36.8)	3636 (63.2)
Site C	16 049 (15.6)	3939 (24.5)	12 110 (75.5)		4879 (30.4)	11 170 (69.6)
Site D	14 009 (13.6)	3598 (25.7)	10 411 (74.3)		3971 (28.3)	10 038 (71.7)
Site E	14 698 (14.3)	2132 (14.5)	12 566 (85.5)		4867 (33.1)	9831 (66.9)
Site F	21 465 (20.9)	5912 (27.5)	15 553 (72.5)		7179 (33.4)	14 286 (66.6)
Site G	28 182 (27.4)	7835 (27.8)	20 347 (72.2)		10 901 (38.7)	17 281 (61.3)
Median age (IQR), years	5 (2, 10)	4 (1.7, 9)	6 (2, 11)		7 (4, 11)	4 (2, 10)
Age group
6 months–4 years	45 377 (44.1)	13 751 (30.3)	31 626 (69.7)	0.260	10 954 (24.1)	34 423 (75.9)	0.401
5–17 years	57 477 (55.9)	11 817 (20.6)	45 660 (79.4)		23 986 (41.7)	33 491 (58.3)
Female	47 676 (46.4)	11 530 (24.2)	36 146 (75.8)	0.034	16 671 (35.0)	31 005 (65.0)	0.041
Race/ethnicity
Black Non-Hispanic	10 078 (9.8)	1613 (16.0)	8465 (84.0)	0.249	3703 (36.7)	6375 (63.3)	0.112
Hispanic	35 310 (34.3)	8770 (24.8)	26 540 (75.2)		12 756 (36.1)	22 554 (63.9)
Other Non-Hispanic^b	13 184 (12.8)	4641 (35.2)	8543 (64.8)		4644 (35.2)	8540 (64.8)
Unknown	4745 (4.6)	1150 (24.2)	3595 (75.8)		1631 (34.4)	3114 (65.6)
White Non-Hispanic	39 537 (38.4)	9394 (23.8)	30 143 (76.2)		12 206 (30.9)	27 331 (69.1)
Influenza type
Influenza A only	29 262 (83.7)	5148 (17.6)	24 114 (82.4)	0.115	29 262 (100.0)	0 (0.0)	–
Influenza B only	5610 (16.1)	759 (13.5)	4851 (86.5)		5610 (100.0)	0 (0.0)
Influenza A and B	68 (0.2)	5 (7.4)	63 (92.6)		68 (100.0)	0 (0.0)

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Abbreviations: ED/UC, emergency department/urgent care; ICU, intensive care unit; IQR, interquartile range; SMD, standardized mean difference.

^aAn absolute SMD >0.20 indicates a non-negligible difference in variable distributions between vaccinated versus unvaccinated encounters or for encounters with positive influenza test results versus negative influenza test results.

^bOther race is defined as any one of the following responses: Asian, Hawaiian or other Pacific Islander, American Indian or Alaska Native, Middle Eastern or North African, Other, or multiple races.

^cIncludes respiratory conditions (asthma, COPD, other lung conditions) and non-respiratory conditions (cardiovascular, neurologic, hematologic, endocrine, renal, gastrointestinal).

^dPatients were considered immunocompromised if they had ≥1 ICD-10 discharge diagnosis code for any of the following conditions: hematologic malignancy, solid malignancy, bone marrow transplant, solid organ transplant, rheumatologic/inflammatory disorder, other intrinsic immunodeficiency condition, or HIV/AIDS.

Forest plots showing VE point estimates and CIs against influenza-associated pediatric hospitalizations and ED/UC encounters. Among hospitalizations, forest plots are shown for the overall VE estimate and by time since vaccination, influenza type, age group, immune status, and critical illness outcome. Among ED/UC encounters, forest plots are shown for the overall VE estimate and by time since vaccination, influenza type, age group, and setting (ED or UC). — Influenza vaccine effectiveness against influenza-associated hospitalizations and emergency department or urgent care encounters among children aged 6 months–17 years—VISION, October 2024–April 2025. Abbreviations: CI, confidence interval; ED, emergency department; ICU, intensive care unit; IQR, interquartile range; UC, urgent care; VE, vaccine effectiveness. ^aVE was estimated using multivariable logistic regression models comparing the odds of influenza vaccination between influenza-positive cases and influenza-negative controls. Models were adjusted for age, sex, race and ethnicity, calendar day, and site. Age and calendar day were treated as natural cubic splines with 4 degrees of freedom. ^bInfluenza A and B coinfections were excluded from influenza A and B case counts and from VE estimates against influenza A and B. ^cPatients were considered immunocompromised if they had ≥1 ICD-10 discharge diagnosis code for any of the following conditions: hematologic malignancy, solid malignancy, bone marrow transplant, solid organ transplant, rheumatologic/inflammatory disorder, other intrinsic immunodeficiency condition, or HIV/AIDS. ^dDue to the small number of cases, VE could not be determined among immunocompromised children or against in-hospital pediatric death. ^eTo estimate VE against ICU admission, cases were restricted to encounters with ICU admission and no in-hospital death. ^fED and UC encounters occurring within 7 days of each other in the same patient were excluded from the ED-only and UC-only estimates.

Of 102 854 ARI-associated ED/UC encounters in children, 34 940 (34.0%) were influenza-positive cases and 67 914 (66.0%) were influenza-negative controls (Table 1). Influenza positivity among ARI-associated ED/UC encounters included in this analysis was 24.1% among children aged 6 months–4 years and 41.7% among those aged 5–17 years. Overall, 25 568 (24.9%) had received an influenza vaccine before the encounter (16.9% of cases versus 28.9% of controls, Figure 1). Among vaccinated patients, median time since vaccination was 95 days.

Across care settings, 84.5% of vaccinated children with a known product type received standard-dose, egg-based inactivated vaccine; 9.8% received cell-culture-based vaccine; 4.0% received live-attenuated vaccine; and 1.7% received a different product type (Supplementary Table 4).

Pediatric Vaccine Effectiveness

Overall VE against pediatric influenza-associated hospitalizations was 51% (95% confidence interval [95% CI]: 41–60) (Figure 1). VE among children aged 6 months–4 years was 58% (95% CI: 45–68), and VE among children aged 5–17 years was 45% (95% CI: 30–57). VE was 48% (95% CI: 37–58) against influenza A and 67% (95% CI: 40–82) against influenza B. VE against ICU admission was 66% (95% CI: 49–79). Due to the small number of cases, VE could not be determined among immunocompromised children or against in-hospital pediatric death.

Overall VE against pediatric influenza-associated ED/UC encounters was 54% (95% CI: 52%–55%) (Figure 1). VE among children aged 6 months–4 years was 61% (95% CI: 58–63), and VE among children aged 5–17 years was 47% (95% CI: 45–50). VE was 50% (95% CI: 48–52) against influenza A and 69% (95% CI: 66–72) against influenza B.

Adult Patient Characteristics

Of 76 072 ARI-associated hospitalizations in adults, 11 178 (14.7%) were influenza-positive cases and 64 894 (85.3%) were influenza-negative controls (Table 2). Influenza positivity among ARI-associated hospitalizations included in this analysis was 17.6% among adults aged 18–49 years, 15.7% among adults aged 50–64 years, and 13.9% among adults aged ≥65 years. Median age was 71 years for cases and 72 years for controls. Overall, 37 502 (49.3%) hospitalized adults had received an influenza vaccine before their encounter (39.7% of cases versus 51.0% of controls, Figure 2). Among those vaccinated, median time since vaccination was 109 days. A total of 15 456 (20.3%) hospitalized adults were admitted to an ICU during their admission, and 5335 (7.0%) died.

Table 2.

Characteristics of Acute Respiratory Illness-Associated Hospitalizations and Emergency Department/Urgent Care Encounters Among Adults Aged ≥18 Years by Influenza Vaccination and Test Status—VISION, October 2024–April 2025

		Influenza Vaccination Status			Influenza Test Result
	Total (col %)	Vaccinated (row %)	Unvaccinated (row %)	SMD^a	Positive (row %)	Negative (row %)	SMD^a
All hospitalizations	76 072	37 502 (49.3)	38 570 (50.7)		11 178 (14.7)	64 894 (85.3)
Influenza vaccination status
Unvaccinated	38 570 (50.7)	0 (0.0)	38 570 (100.0)	–	6741 (17.5)	31 829 (82.5)	0.228
Vaccinated	37 502 (49.3)	37 502 (100.0)	0 (0.0)		4437 (11.8)	33 065 (88.2)
14–59 days earlier	7697 (10.1)	7697 (100.0)	0 (0.0)		468 (6.1)	7229 (93.9)
60–119 days earlier	13 382 (17.6)	13 382 (100.0)	0 (0.0)		2029 (15.2)	11 353 (84.8)
≥120 days earlier	16 423 (21.6)	16 423 (100.0)	0 (0.0)		1940 (11.8)	14 483 (88.2)
Month of encounter
October 2024	5386 (7.1)	1602 (29.7)	3784 (70.3)	0.273	50 (0.9)	5336 (99.1)	0.919
November 2024	8311 (10.9)	3559 (42.8)	4752 (57.2)		225 (2.7)	8086 (97.3)
December 2024	12 453 (16.4)	5912 (47.5)	6541 (52.5)		2149 (17.3)	10 304 (82.7)
January 2025	14 921 (19.6)	7493 (50.2)	7428 (49.8)		3729 (25.0)	11 192 (75.0)
February 2025	13 468 (17.7)	6934 (51.5)	6534 (48.5)		3526 (26.2)	9942 (73.8)
March 2025	12 102 (15.9)	6569 (54.3)	5533 (45.7)		1213 (10.0)	10 889 (90.0)
April 2025	9431 (12.4)	5433 (57.6)	3998 (42.4)		286 (3.0)	9145 (97.0)
Site
Site A	2741 (3.6)	1339 (48.9)	1402 (51.1)	0.482	413 (15.1)	2328 (84.9)	0.097
Site B	3783 (5.0)	2041 (54.0)	1742 (46.0)		630 (16.7)	3153 (83.3)
Site C	7668 (10.1)	2884 (37.6)	4784 (62.4)		1117 (14.6)	6551 (85.4)
Site D	9322 (12.3)	3698 (39.7)	5624 (60.3)		1171 (12.6)	8151 (87.4)
Site E	19 090 (25.1)	6949 (36.4)	12 141 (63.6)		3101 (16.2)	15 989 (83.8)
Site F	20 401 (26.8)	12 094 (59.3)	8307 (40.7)		2890 (14.2)	17 511 (85.8)
Site G	13 067 (17.2)	8497 (65.0)	4570 (35.0)		1856 (14.2)	11 211 (85.8)
Median age (IQR), years	72 (61, 81)	76 (67, 84)	68 (55, 78)		71 (59, 80)	72 (61, 82)
Age group
18–49 years	9668 (12.7)	2528 (26.1)	7140 (73.9)	0.502	1706 (17.6)	7962 (82.4)	0.104
50–64 years	14 374 (18.9)	5125 (35.7)	9249 (64.3)		2261 (15.7)	12 113 (84.3)
≥65 years	52 030 (68.4)	29 849 (57.4)	22 181 (42.6)		7211 (13.9)	44 819 (86.1)
Female	40 280 (52.9)	19 921 (49.5)	20 359 (50.5)	0.007	6153 (15.3)	34 127 (84.7)	0.049
Race/ethnicity
Black Non-Hispanic	7482 (9.8)	3000 (40.1)	4482 (59.9)	0.191	1095 (14.6)	6387 (85.4)	0.034
Hispanic	10 243 (13.5)	5362 (52.3)	4881 (47.7)		1586 (15.5)	8657 (84.5)
Other Non-Hispanic^b	7334 (9.6)	4294 (58.5)	3040 (41.5)		1123 (15.3)	6211 (84.7)
Unknown	1111 (1.5)	350 (31.5)	761 (68.5)		146 (13.1)	965 (86.9)
White Non-Hispanic	49 902 (65.6)	24 496 (49.1)	25 406 (50.9)		7228 (14.5)	42 674 (85.5)
Any underlying medical condition^c	70 047 (92.1)	35 643 (50.9)	34 404 (49.1)	0.218	9722 (13.9)	60 325 (86.1)	0.200
Respiratory condition	37 568 (49.4)	19 909 (53.0)	17 659 (47.0)	0.146	4817 (12.8)	32 751 (87.2)	0.148
Non-respiratory condition	66 663 (87.6)	34 530 (51.8)	32 133 (48.2)	0.269	9110 (13.7)	57 553 (86.3)	0.203
Immunocompromising condition^d	18 387 (24.2)	10 314 (56.1)	8073 (43.9)	0.154	1921 (10.4)	16 466 (89.6)	0.201
Influenza type
Influenza A only	10 832 (96.9)	4340 (40.1)	6492 (59.9)	0.090	10 832 (100.0)	0 (0.0)	–
Influenza B only	334 (3.0)	93 (27.8)	241 (72.2)		334 (100.0)	0 (0.0)
Influenza A and B	12 (0.1)	4 (33.3)	8 (66.7)		12 (100.0)	0 (0.0)
ICU admission
Yes	15 456 (20.3)	7389 (47.8)	8067 (52.2)	0.039	1755 (11.4)	13 701 (88.6)	0.141
No	60 249 (79.2)	29 898 (49.6)	30 351 (50.4)		9379 (15.6)	50 870 (84.4)
Unknown	367 (0.5)	215 (58.6)	152 (41.4)		44 (12.0)	323 (88.0)
In-hospital death
Yes	5335 (7.0)	2813 (52.7)	2522 (47.3)	0.038	444 (8.3)	4891 (91.7)	0.154
No	70 736 (93.0)	34 689 (49.0)	36 047 (51.0)		10 734 (15.2)	60 002 (84.8)
Unknown	1 (0.0)	0 (0.0)	1 (100.0)		0 (0.0)	1 (100.0)
All ED/UC encounters	233 411	86 890 (37.2)	146 521 (62.8)		66 299 (28.4)	167 112 (71.6)
Influenza vaccination status
Unvaccinated	146 521 (62.8)	0 (0.0)	146 521 (100.0)	–	48 904 (33.4)	97 617 (66.6)	0.329
Vaccinated	86 890 (37.2)	86 890 (100.0)	0 (0.0)		17 395 (20.0)	69 495 (80.0)
14–59 days earlier	17 715 (7.6)	17 715 (100.0)	0 (0.0)		2045 (11.5)	15 670 (88.5)
60–119 days earlier	33 251 (14.2)	33 251 (100.0)	0 (0.0)		8458 (25.4)	24 793 (74.6)
≥120 days earlier	35 924 (15.4)	35 924 (100.0)	0 (0.0)		6892 (19.2)	29 032 (80.8)
Month of encounter
October 2024	17 282 (7.4)	3619 (20.9)	13 663 (79.1)	0.271	460 (2.7)	16 822 (97.3)	0.848
November 2024	22 232 (9.5)	7645 (34.4)	14 587 (65.6)		1902 (8.6)	20 330 (91.4)
December 2024	45 178 (19.4)	15 469 (34.2)	29 709 (65.8)		16 149 (35.7)	29 029 (64.3)
January 2025	52 760 (22.6)	19 442 (36.8)	33 318 (63.2)		23 341 (44.2)	29 419 (55.8)
February 2025	41 490 (17.8)	16 061 (38.7)	25 429 (61.3)		16 326 (39.3)	25 164 (60.7)
March 2025	31 174 (13.4)	13 672 (43.9)	17 502 (56.1)		6030 (19.3)	25 144 (80.7)
April 2025	23 295 (10.0)	10 982 (47.1)	12 313 (52.9)		2091 (9.0)	21 204 (91.0)
Site
Site A	10 075 (4.3)	4003 (39.7)	6072 (60.3)	0.382	2744 (27.2)	7331 (72.8)	0.137
Site B	16 024 (6.9)	6007 (37.5)	10 017 (62.5)		4315 (26.9)	11 709 (73.1)
Site C	28 168 (12.1)	7450 (26.4)	20 718 (73.6)		8234 (29.2)	19 934 (70.8)
Site D	26 121 (11.2)	8309 (31.8)	17 812 (68.2)		6288 (24.1)	19 833 (75.9)
Site E	28 977 (12.4)	6271 (21.6)	22 706 (78.4)		7546 (26.0)	21 431 (74.0)
Site F	55 862 (23.9)	24 084 (43.1)	31 778 (56.9)		15 181 (27.2)	40 681 (72.8)
Site G	68 184 (29.2)	30 766 (45.1)	37 418 (54.9)		21 991 (32.3)	46 193 (67.7)
Median age (IQR), years	51 (34, 70)	67 (48, 78)	43 (30, 60)		45 (31, 63)	54 (35, 72)
Age group
18–49 years	111 376 (47.7)	23 220 (20.8)	88 156 (79.2)	0.818	37 606 (33.8)	73 770 (66.2)	0.315
50–64 years	46 203 (19.8)	16 824 (36.4)	29 379 (63.6)		13 706 (29.7)	32 497 (70.3)
≥65 years	75 832 (32.5)	46 846 (61.8)	28 986 (38.2)		14 987 (19.8)	60 845 (80.2)
Female	138 796 (59.5)	52 572 (37.9)	86 224 (62.1)	0.034	38 534 (27.8)	100 262 (72.2)	0.038
Race/ethnicity
Black Non-Hispanic	23 755 (10.2)	6954 (29.3)	16 801 (70.7)	0.202	6532 (27.5)	17 223 (72.5)	0.197
Hispanic	58 249 (25.0)	20 333 (34.9)	37 916 (65.1)		19 953 (34.3)	38 296 (65.7)
Other Non-Hispanic^b	27 021 (11.6)	12 453 (46.1)	14 568 (53.9)		7994 (29.6)	19 027 (70.4)
Unknown	5573 (2.4)	1351 (24.2)	4222 (75.8)		2065 (37.1)	3508 (62.9)
White Non-Hispanic	118 813 (50.9)	45 799 (38.5)	73 014 (61.5)		29 755 (25.0)	89 058 (75.0)
Influenza type
Influenza A only	60 663 (91.5)	16 568 (27.3)	44 095 (72.7)	0.196	60 663 (100.0)	0 (0.0)	–
Influenza B only	5582 (8.4)	817 (14.6)	4765 (85.4)		5582 (100.0)	0 (0.0)
Influenza A and B	54 (0.1)	10 (18.5)	44 (81.5)		54 (100.0)	0 (0.0)

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Abbreviations: ED/UC, emergency department/urgent care; ICU, intensive care unit; IQR, interquartile range; SMD, standardized mean difference.

^bOther race is defined as any one of the following responses: Asian, Hawaiian or other Pacific Islander, American Indian or Alaska Native, Other, Middle Eastern or North African, or multiple races.

^cIncludes respiratory conditions (asthma, COPD, other lung conditions) and non-respiratory conditions (cardiovascular, neurologic, hematologic, endocrine, renal, gastrointestinal).

Forest plots showing VE point estimates and CIs against influenza-associated hospitalizations and ED/UC encounters among adults. Among hospitalizations, forest plots are shown for the overall VE estimate and by time since vaccination, influenza type, age group, immune status, and critical illness outcome. Among ED/UC encounters, forest plots are shown for the overall VE estimate and by time since vaccination, influenza type, age group, and setting (ED or UC). — Influenza vaccine effectiveness against influenza-associated hospitalizations and emergency department or urgent care encounters among adults aged ≥18 years—VISION, October 2024–April 2025. Abbreviations: CI, confidence interval; ED, emergency department; ICU, intensive care unit; IQR, interquartile range; UC, urgent care; VE, vaccine effectiveness. ^aVE was estimated using multivariable logistic regression models comparing the odds of influenza vaccination between influenza-positive cases and influenza-negative controls. Models were adjusted for age, sex, race and ethnicity, calendar day, and site. Age and calendar day were treated as natural cubic splines with 4 degrees of freedom. ^bInfluenza A and B coinfections were excluded from influenza A and B case counts and from VE estimates against influenza A and B. ^cPatients were considered immunocompromised if they had ≥1 ICD-10 discharge diagnosis code for any of the following conditions: hematologic malignancy, solid malignancy, bone marrow transplant, solid organ transplant, rheumatologic/inflammatory disorder, other intrinsic immunodeficiency condition, or HIV/AIDS. ^dTo estimate VE against ICU admission, cases were restricted to encounters with ICU admission and no in-hospital death. ^eED and UC encounters occurring within 7 days of each other were excluded from the ED-only and UC-only estimates.

Of 233 411 ARI-associated ED/UC encounters in adults, 66 299 (28.4%) were influenza-positive cases and 167 112 (71.6%) were influenza-negative controls (Table 2). Influenza positivity among ARI-associated ED/UC encounters included in this analysis was 33.8% among adults aged 18–49 years, 29.7% among adults aged 50–64 years, and 19.8% among adults aged ≥65 years. Median age was 45 years for cases and 54 years for controls. Overall, 86 890 (37.2%) had received an influenza vaccine before the encounter (26.2% of cases versus 41.6% of controls, Figure 2). Among vaccinated patients, median time since vaccination was 107 days.

Across care settings, 83.7% of vaccinated adults aged 18–64 years with a known product type received a standard-dose, egg-based inactivated vaccine (Supplementary Table 4). Among adults aged ≥65 years, 92.4% received a high-dose inactivated, adjuvanted, or recombinant vaccine, all of which were preferentially recommended for adults aged ≥65 years [4].

Adult Vaccine Effectiveness

Overall VE against influenza-associated hospitalizations was 43% (95% CI: 41–46) among adults (Figure 2). When stratified by age group, VE was 40% (95% CI: 31–48) among adults aged 18–49 years, 43% (95% CI: 36–49) among adults aged 50–64 years, and 44% (95% CI: 41–48) among adults aged ≥65 years. VE was 43% (95% CI: 40–45) against influenza A and 65% (95% CI: 54–73) against influenza B. Among immunocompetent and immunocompromised adults, VE estimates were 44% (95% CI: 40–47) and 38% (95% CI: 31–44), respectively. VE was 43% (95% CI: 36–49) against ICU admission and 55% (95% CI: 45–63) against in-hospital death.

Overall VE against influenza-associated ED/UC encounters was 49% (95% CI: 47–50) among adults (Figure 2). When stratified by age group, VE was 51% (95% CI: 50–53) among adults aged 18–49 years, 48% (95% CI: 45–50) among adults aged 50–64 years, and 44% (95% CI: 42–47) among adults aged ≥65 years. VE was 46% (95% CI: 45–48) against influenza A and 69% (95% CI: 66–71) against influenza B.

Vaccine Effectiveness by Time Since Vaccination

Among both children and adults, influenza vaccination provided protection against influenza-associated hospitalizations and ED/UC encounters through ≥120 days after vaccination (Figures 1–3, Supplementary Table 5). Among children, VE against hospitalizations was 59% (95% CI: 40–72) at 14–59 days, 53% (95% CI: 39–64) at 60–119 days, and 45% (95% CI: 26–60) at ≥120 days after vaccination (Figure 1). VE against ED/UC encounters was 60% (95% CI: 57–63) at 14–59 days, 54% (95% CI: 52–56) at 60–119 days, and 48% (95% CI: 45–51) at ≥120 days after vaccination. VE estimates stratified by influenza type, age group, and time since vaccination are shown in Figure 3 and Supplementary Table 5. Among children aged 6 months–4 years, VE did not decline against influenza A or influenza B-associated ED/UC encounters through ≥120 days after vaccination (Figure 3B, Supplementary Table 5). However, among children aged 5–17 years, VE estimates against influenza A and influenza B-associated ED/UC encounters were significantly lower at ≥120 days compared to 14–59 days after vaccination (Figure 3B, Supplementary Table 5).

Forest plots showing VE point estimates and CIs against influenza-associated hospitalizations and ED/UC encounters by influenza type, age group, and time since vaccination. — Influenza vaccine effectiveness against influenza-associated hospitalizations and emergency department or urgent care encounters by influenza type, age group, and time since vaccination—VISION, October 2024–April 2025. ^aVaccine effectiveness estimates are not shown against influenza B-associated hospitalization for some groups due to case counts <50 or confidence interval widths ≥100 percentage points.

Among adults, VE against influenza-associated hospitalizations was 56% (95% CI: 51–60) at 14–59 days, 45% (95% CI: 42–49) at 60–119 days, and 37% (95% CI: 33–41) at ≥120 days after vaccination (Figure 2). VE against ED/UC encounters was 60% (95% CI: 58–62) at 14–59 days, 48% (95% CI: 47–50) at 60–119 days, and 43% (95% CI: 41–45) at ≥120 days after vaccination. VE point estimates against influenza A-associated hospitalizations were similar across adult age groups and generally declined with increasing time since vaccination, although confidence limits overlapped (Figure 3A and 3B, Supplementary Table 5). VE point estimates against influenza A-associated ED/UC encounters were similar across adult age groups and were significantly lower at ≥120 days compared to 14–59 days after vaccination (Figure 3A and 3B, Supplementary Table 5). No consistent trends were observed against influenza B-associated hospitalizations and ED/UC encounters (Figure 3A and 3B, Supplementary Table 5).

DISCUSSION

Seasonal influenza vaccination provided protection against influenza-associated hospitalizations and ED/UC encounters among US children and adults during the 2024–2025 season, with overall VE estimates ranging from 43% to 54%. Similar VE estimates were found among groups at higher risk of severe outcomes due to influenza, such as older adults, adults with immunocompromising conditions, and young children. Protection was also observed against critical illness, including ICU admission in children and ICU admission and in-hospital death in adults. Although VE point estimates were highest during the first 2 months after vaccination, protection against hospitalization and ED/UC encounters was sustained for more than 4 months. Together, these findings support influenza vaccination as an important tool to reduce influenza-associated morbidity and mortality across the lifespan.

The 2024–2025 influenza season was a high-severity season in all age groups, characterized by co-circulation of influenza A(H1N1)pdm09 and A(H3N2) viruses [1, 3]. Co-circulation of both influenza A subtypes may have contributed to the elevated hospitalization rates observed, as well as the highest number of influenza-associated pediatric deaths observed since national reporting began in 2004 [2, 14]. While both subtypes can cause severe illness, influenza A(H3N2)-predominant seasons have been associated with higher hospitalization rates among adults aged ≥65 years, and VE against A(H3N2) has historically been lower than that against A(H1N1) and B, particularly among older adults [15–17]. In the current analysis, influenza vaccination reduced the likelihood of influenza A-associated hospitalizations among children and adults, suggesting that vaccination provided protection against both A(H1N1)pdm09 and A(H3N2) influenza. This finding agrees with data from other US and Northern Hemisphere influenza VE studies [18–20]. Despite antigenic differences between circulating viruses and updated vaccine components, VE estimates from the current analysis against influenza A-associated hospitalizations and ED/UC encounters during the 2024–2025 season (43%–50%) were similar to those from the VISION Network during the 2023–2024 season (37%–49%) [11]. Using established networks that apply the same methodological approach to produce annual VE estimates has the benefit of allowing for comparisons between seasons.

In previous analyses, influenza vaccination has been associated with protection against a variety of critical outcomes, including severe and life-threatening pediatric influenza [6, 21], pediatric influenza-associated deaths [22], and influenza-associated severe outcomes and deaths among adults [5, 11, 23]. Protection has also been found among adults with immunocompromising conditions at increased risk of influenza complications [24]. Results from the current analysis showing that influenza vaccination was associated with protection against influenza-associated ICU admission in children, ICU admission and in-hospital death in adults, and hospitalizations in immunocompromised adults are consistent with these previous findings. Persistence of protection for >4 months after vaccination indicated that vaccine-elicited protection lasted through the 2024–2025 influenza season. Lower VE estimates observed >4 months after vaccination were consistent with observations during the 2023–2024 season [11].

Despite numerous analyses showing the benefits of influenza vaccination, vaccination coverage has decreased in most age groups since the start of the COVID-19 pandemic. From the 2019–2020 season to the 2024–2025 season, influenza vaccination coverage fell from 64% to 50% among US children aged 6 months–17 years and from 70% to 64% among US adults aged ≥65 years [25]. Decreasing influenza vaccination coverage has left an increasing number of US children and adults at higher risk of severe influenza-associated outcomes. However, despite continued declines in coverage, estimates indicate that influenza vaccination still prevented 10 million symptomatic illnesses, 5 million medical visits, 180 000 hospitalizations, and 12 000 deaths during the 2024–2025 season [1]. Improving vaccination coverage could further reduce the burden of influenza-associated disease.

Limitations

This analysis had several limitations. First, because VISION uses clinical testing to classify influenza case status and few cases are subtyped in routine clinical testing, we were unable to estimate VE by influenza A subtype. Second, although vaccination status was determined using multiple data sources, some influenza vaccine doses may not have been documented, resulting in misclassification of influenza vaccination status; however, misclassification would have occurred among both cases and controls, likely resulting in a bias toward the null and an underestimation of influenza VE. Third, due to limited data on influenza vaccination in previous seasons, we were unable to estimate VE among fully vaccinated versus partially vaccinated children aged 6 months–8 years [4]. Fourth, although VE models were adjusted for patient-level demographic characteristics, calendar time, and VISION site, residual confounding from other factors, including influenza infection history, receipt of influenza antiviral treatment, and the use of non-pharmaceutical interventions (eg, masking), is possible. Fifth, findings may not be representative of the entire US population.

Conclusions

Influenza vaccination provided protection against influenza-associated hospitalizations and ED/UC encounters among US children and adults during the high-severity 2024–2025 season. Increased uptake of influenza vaccine could reduce the burden of influenza and its complications.

Supplementary Material

ofag473_Supplementary_Data

ofag473_supplementary_data.docx^{(414.4KB, docx)}

Notes

Disclaimer. The findings and conclusions of this report are those of the authors and do not necessarily reflect the official position of the Centers for Disease Control and Prevention.

Financial support. This study was supported by the CDC through contract 75D30121D12779 to Westat, Inc. and contracts 75D30123C17595 and 75D30123C18039 to Kaiser Foundation Hospitals.

Patient consent statement. This activity was reviewed by CDC, deemed not research or research not involving human subjects, and was conducted consistent with applicable federal law and CDC policy (see eg, 45C.F.R. part 46, 21C.F.R. part 56; 42 U.S.C. §241(d); 5 U.S.C. §552a; 44 U.S.C. §3501 et seq). Patient informed consent was not required.

Data sharing. Data sharing agreements between the CDC and VISION partner institutions prohibit the CDC from making VISION data publicly available.

Contributor Information

Jennifer DeCuir, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

Emily L Reeves, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

Zachary A Weber, Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA.

Duck-Hye Yang, Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA.

Stephanie A Irving, Kaiser Permanente Center for Health Research, Portland, Oregon, USA.

Sara Y Tartof, Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA; Kaiser Permanente Bernard J Tyson School of Medicine, Pasadena, California, USA.

Nicola P Klein, Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA.

Shaun J Grannis, Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA; School of Medicine, Indiana University, Indianapolis, Indiana, USA.

Toan C Ong, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.

Sarah W Ball, Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA.

Malini B DeSilva, Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA.

Kristin Dascomb, Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA.

Allison L Naleway, Kaiser Permanente Center for Health Research, Portland, Oregon, USA.

Padma Koppolu, Kaiser Permanente Center for Health Research, Portland, Oregon, USA.

S Bianca Salas, Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA.

Lina S Sy, Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA.

Bruno Lewin, Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA; Kaiser Permanente Bernard J Tyson School of Medicine, Pasadena, California, USA.

Richard Contreras, Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California, USA.

Ousseny Zerbo, Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA.

John R Hansen, Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA.

Lawrence Block, Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA.

Karen B Jacobson, Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California, USA.

Brian E Dixon, Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA; Fairbanks School of Public Health, Indiana University Indianapolis, Indianapolis, Indiana, USA.

Colin Rogerson, Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA; School of Medicine, Indiana University, Indianapolis, Indiana, USA.

Thomas Duszynski, Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA; Fairbanks School of Public Health, Indiana University Indianapolis, Indianapolis, Indiana, USA.

William F Fadel, Center for Biomedical Informatics, Regenstrief Institute, Indianapolis, Indiana, USA; Fairbanks School of Public Health, Indiana University Indianapolis, Indianapolis, Indiana, USA.

Michelle A Barron, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.

David Mayer, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.

Catia Chavez, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.

Adam Yates, Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA.

Lindsey Kirshner, Clinical Research Practice, Westat, Inc., Bethesda, Maryland, USA.

Charlene E McEvoy, Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA; Pulmonary, Critical Care and Sleep Department, HealthPartners Institute, Minneapolis, Minnesota, USA.

Omobosola O Akinsete, Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA; Infectious Disease Department, HealthPartners Institute, Minneapolis, Minnesota, USA.

Inih J Essien, Department of Research, HealthPartners Institute, Minneapolis, Minnesota, USA.

Tamara Sheffield, Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA; Immunization Programs, Intermountain Health, Salt Lake City, Utah, USA.

Daniel Bride, Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA; Enterprise Analytics, Intermountain Health, Salt Lake City, Utah, USA.

Julie Arndorfer, Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA.

Josh Van Otterloo, Division of Infectious Diseases and Clinical Epidemiology, Intermountain Health, Salt Lake City, Utah, USA.

Karthik Natarajan, Department of Biomedical Informatics, Columbia University Irving Medical Center, New York, New York, USA; Medical Informatics Services, New York-Presbyterian Hospital, New York, New York, USA.

Caitlin S Ray, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

Amanda B Payne, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

Katherine Adams, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

Brendan Flannery, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

Shikha Garg, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

Supplementary Data

Supplementary materials are available at Open Forum Infectious Diseases online. Consisting of data provided by the authors to benefit the reader, the posted materials are not copyedited and are the sole responsibility of the authors, so questions or comments should be addressed to the corresponding author.

References

1. Centers for Disease Control and Prevention . 2024–2025 influenza season summary: severity, disease burden, and burden prevented. Available at: https://www.cdc.gov/flu-burden/php/data-vis-vac/2024-2025-prevented.html. Accessed 13 April 2026.
2. O’Halloran A, Habeck JW, Gilmer M, et al. Influenza-associated hospitalizations during a high severity season—Influenza Hospitalization Surveillance Network, United States, 2024–25 influenza season. MMWR Morb Mortal Wkly Rep 2025; 74:529–37. [DOI] [PMC free article] [PubMed] [Google Scholar]
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4. Grohskopf L, Ferdinands J, Blanton L, Broder K, Loehr J. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices—United States, 2024–25 influenza season. MMWR Recomm Rep 2024; 73:1–25. [DOI] [PMC free article] [PubMed] [Google Scholar]
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6. Sumner KM, Sahni LC, Boom JA, et al. Estimated vaccine effectiveness for pediatric patients with severe influenza, 2015–2020. JAMA Netw Open 2024; 7:e2452512. [DOI] [PMC free article] [PubMed] [Google Scholar]
7. White EB, Grant L, Mak J, et al. Influenza vaccine effectiveness against illness and asymptomatic infection in 2022–2023: a prospective cohort study. Clin Infect Dis 2025; 80:893–900. [DOI] [PMC free article] [PubMed] [Google Scholar]
8. Chung JR, Price AM, Zimmerman RK, et al. Influenza vaccine effectiveness against medically attended outpatients illness, United States, 2023–2024 season. Clin Infect Dis 2025; 81:e184–91. [DOI] [PMC free article] [PubMed] [Google Scholar]
9. Centers for Disease Control and Prevention . CDC seasonal flu vaccine effectiveness studies. Available at: https://www.cdc.gov/flu-vaccines-work/php/effectiveness-studies/index.html. Accessed 13 April 2026.
10. Centers for Disease Control and Prevention . VISION vaccine effectiveness network. Available at: https://www.cdc.gov/flu-vaccines-work/php/vaccine-effectiveness/vision-network.html. Accessed 13 April 2026.
11. Tenforde MW, Reeves EL, Weber ZA, et al. Influenza vaccine effectiveness against hospitalizations and emergency department or urgent care encounters for children, adolescents, and adults during the 2023–2024 season, United States. Clin Infect Dis 2025; 81:667–78. [DOI] [PMC free article] [PubMed] [Google Scholar]
12. Doll MK, Pettigrew SM, Ma J, Verma A. Effects of confounding bias in coronavirus disease 2019 (COVID-19) and influenza vaccine effectiveness test-negative designs due to correlated influenza and COVID-19 vaccination behaviors. Clin Infect Dis 2022; 75:e564–71. [DOI] [PMC free article] [PubMed] [Google Scholar]
13. Lewis NM, Harker EJ, Leis A, et al. Assessment and mitigation of bias in influenza and COVID-19 vaccine effectiveness analyses—IVY Network, September 1, 2022–March 30, 2023. Vaccine 2025; 43:126492. [DOI] [PMC free article] [PubMed] [Google Scholar]
14. Centers for Disease Control and Prevention . FluView interactive: influenza-associated pediatric mortality. Available at: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html. Accessed 13 April 2026.
15. Budd AP, Beacham L, Smith CB, et al. Birth cohort effects in influenza surveillance data: evidence that first influenza infection affects later influenza-associated illness. J Infect Dis 2019; 220:820–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
16. Belongia EA, Simpson MD, King JP, et al. Variable influenza vaccine effectiveness by subtype: a systematic review and meta-analysis of test-negative design studies. Lancet Infect Dis 2016; 16:942–51. [DOI] [PubMed] [Google Scholar]
17. Okoli GN, Racovitan F, Abdulwahid T, Righolt CH, Mahmud SM. Variable seasonal influenza vaccine effectiveness across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains: a systematic review and meta-analysis of the evidence from test-negative design studies after the 2009/10 influenza pandemic. Vaccine 2021; 39:1225–40. [DOI] [PubMed] [Google Scholar]
18. Frutos AM. Interim estimates of 2024–2025 seasonal influenza vaccine effectiveness—four vaccine effectiveness networks, United States, October 2024–February 2025. MMWR Morb Mortal Wkly Rep 2025; 74:83–90. [DOI] [PMC free article] [PubMed] [Google Scholar]
19. Rose AM, Lucaccioni H, Marsh K, et al. Interim 2024/25 influenza vaccine effectiveness: eight European studies, September 2024 to January 2025. Euro Surveill 2025; 30:2500102. [DOI] [PMC free article] [PubMed] [Google Scholar]
20. Separovic L, Zhan Y, Kaweski SE, et al. Interim estimates of vaccine effectiveness against influenza A(H1N1)pdm09 and A(H3N2) during a delayed influenza season, Canada, 2024/25. Euro Surveill 2025; 30:2500059. [DOI] [PMC free article] [PubMed] [Google Scholar]
21. Olson SM, Newhams MM, Halasa NB, et al. Vaccine effectiveness against life-threatening influenza illness in US children. Clin Infect Dis 2022; 75:230–8. [DOI] [PubMed] [Google Scholar]
22. Flannery B, Reynolds SB, Blanton L, et al. Influenza vaccine effectiveness against pediatric deaths: 2010–2014. Pediatrics 2017; 139:e20164244. [DOI] [PMC free article] [PubMed] [Google Scholar]
23. Lewis NM, Harker EJ, Cleary S, et al. Vaccine effectiveness against influenza A(H1N1), A(H3N2), and B-associated hospitalizations, United States, 1 September 2023 to 31 May 2024. J Infect Dis 2025; 232:e626–36. [DOI] [PMC free article] [PubMed] [Google Scholar]
24. Scott J, Abers MS, Marwah HK, et al. Updated evidence for COVID-19, RSV, and influenza vaccines for 2025–2026. N Engl J Med 2025; 393:2221–42. [DOI] [PubMed] [Google Scholar]
25. Centers for Disease Control and Prevention . Influenza vaccination coverage for persons 6 months and older. Available at: https://www.cdc.gov/fluvaxview/interactive/general-population-coverage.html. Accessed 13 April 2026.

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ofag473_Supplementary_Data

ofag473_supplementary_data.docx^{(414.4KB, docx)}

[ofag473-B1] 1. Centers for Disease Control and Prevention . 2024–2025 influenza season summary: severity, disease burden, and burden prevented. Available at: https://www.cdc.gov/flu-burden/php/data-vis-vac/2024-2025-prevented.html. Accessed 13 April 2026.

[ofag473-B2] 2. O’Halloran A, Habeck JW, Gilmer M, et al. Influenza-associated hospitalizations during a high severity season—Influenza Hospitalization Surveillance Network, United States, 2024–25 influenza season. MMWR Morb Mortal Wkly Rep 2025; 74:529–37. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B3] 3. Centers for Disease Control and Prevention . Influenza activity in the United States during the 2024–25 season and composition of the 2025–26 influenza vaccine. 2025. Available at: https://www.cdc.gov/flu/whats-new/2025-2026-influenza-activity.html. Accessed 13 April 2026.

[ofag473-B4] 4. Grohskopf L, Ferdinands J, Blanton L, Broder K, Loehr J. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices—United States, 2024–25 influenza season. MMWR Recomm Rep 2024; 73:1–25. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B5] 5. Lewis NM, Zhu Y, Peltan ID, et al. Vaccine effectiveness against influenza A–associated hospitalization, organ failure, and death: United States, 2022–2023. Clin Infect Dis 2024; 78:1056–64. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B6] 6. Sumner KM, Sahni LC, Boom JA, et al. Estimated vaccine effectiveness for pediatric patients with severe influenza, 2015–2020. JAMA Netw Open 2024; 7:e2452512. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B7] 7. White EB, Grant L, Mak J, et al. Influenza vaccine effectiveness against illness and asymptomatic infection in 2022–2023: a prospective cohort study. Clin Infect Dis 2025; 80:893–900. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B8] 8. Chung JR, Price AM, Zimmerman RK, et al. Influenza vaccine effectiveness against medically attended outpatients illness, United States, 2023–2024 season. Clin Infect Dis 2025; 81:e184–91. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B9] 9. Centers for Disease Control and Prevention . CDC seasonal flu vaccine effectiveness studies. Available at: https://www.cdc.gov/flu-vaccines-work/php/effectiveness-studies/index.html. Accessed 13 April 2026.

[ofag473-B10] 10. Centers for Disease Control and Prevention . VISION vaccine effectiveness network. Available at: https://www.cdc.gov/flu-vaccines-work/php/vaccine-effectiveness/vision-network.html. Accessed 13 April 2026.

[ofag473-B11] 11. Tenforde MW, Reeves EL, Weber ZA, et al. Influenza vaccine effectiveness against hospitalizations and emergency department or urgent care encounters for children, adolescents, and adults during the 2023–2024 season, United States. Clin Infect Dis 2025; 81:667–78. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B12] 12. Doll MK, Pettigrew SM, Ma J, Verma A. Effects of confounding bias in coronavirus disease 2019 (COVID-19) and influenza vaccine effectiveness test-negative designs due to correlated influenza and COVID-19 vaccination behaviors. Clin Infect Dis 2022; 75:e564–71. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B13] 13. Lewis NM, Harker EJ, Leis A, et al. Assessment and mitigation of bias in influenza and COVID-19 vaccine effectiveness analyses—IVY Network, September 1, 2022–March 30, 2023. Vaccine 2025; 43:126492. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B14] 14. Centers for Disease Control and Prevention . FluView interactive: influenza-associated pediatric mortality. Available at: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html. Accessed 13 April 2026.

[ofag473-B15] 15. Budd AP, Beacham L, Smith CB, et al. Birth cohort effects in influenza surveillance data: evidence that first influenza infection affects later influenza-associated illness. J Infect Dis 2019; 220:820–9. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B16] 16. Belongia EA, Simpson MD, King JP, et al. Variable influenza vaccine effectiveness by subtype: a systematic review and meta-analysis of test-negative design studies. Lancet Infect Dis 2016; 16:942–51. [DOI] [PubMed] [Google Scholar]

[ofag473-B17] 17. Okoli GN, Racovitan F, Abdulwahid T, Righolt CH, Mahmud SM. Variable seasonal influenza vaccine effectiveness across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains: a systematic review and meta-analysis of the evidence from test-negative design studies after the 2009/10 influenza pandemic. Vaccine 2021; 39:1225–40. [DOI] [PubMed] [Google Scholar]

[ofag473-B18] 18. Frutos AM. Interim estimates of 2024–2025 seasonal influenza vaccine effectiveness—four vaccine effectiveness networks, United States, October 2024–February 2025. MMWR Morb Mortal Wkly Rep 2025; 74:83–90. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B19] 19. Rose AM, Lucaccioni H, Marsh K, et al. Interim 2024/25 influenza vaccine effectiveness: eight European studies, September 2024 to January 2025. Euro Surveill 2025; 30:2500102. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B20] 20. Separovic L, Zhan Y, Kaweski SE, et al. Interim estimates of vaccine effectiveness against influenza A(H1N1)pdm09 and A(H3N2) during a delayed influenza season, Canada, 2024/25. Euro Surveill 2025; 30:2500059. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B21] 21. Olson SM, Newhams MM, Halasa NB, et al. Vaccine effectiveness against life-threatening influenza illness in US children. Clin Infect Dis 2022; 75:230–8. [DOI] [PubMed] [Google Scholar]

[ofag473-B22] 22. Flannery B, Reynolds SB, Blanton L, et al. Influenza vaccine effectiveness against pediatric deaths: 2010–2014. Pediatrics 2017; 139:e20164244. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B23] 23. Lewis NM, Harker EJ, Cleary S, et al. Vaccine effectiveness against influenza A(H1N1), A(H3N2), and B-associated hospitalizations, United States, 1 September 2023 to 31 May 2024. J Infect Dis 2025; 232:e626–36. [DOI] [PMC free article] [PubMed] [Google Scholar]

[ofag473-B24] 24. Scott J, Abers MS, Marwah HK, et al. Updated evidence for COVID-19, RSV, and influenza vaccines for 2025–2026. N Engl J Med 2025; 393:2221–42. [DOI] [PubMed] [Google Scholar]

[ofag473-B25] 25. Centers for Disease Control and Prevention . Influenza vaccination coverage for persons 6 months and older. Available at: https://www.cdc.gov/fluvaxview/interactive/general-population-coverage.html. Accessed 13 April 2026.

PERMALINK

Influenza Vaccine Effectiveness Against Influenza-Associated Hospitalizations and Emergency Department or Urgent Care Encounters Among Children and Adults—VISION, United States, 2024–2025 Season

Jennifer DeCuir

Emily L Reeves

Zachary A Weber

Duck-Hye Yang

Stephanie A Irving

Sara Y Tartof

Nicola P Klein

Shaun J Grannis

Toan C Ong

Sarah W Ball

Malini B DeSilva

Kristin Dascomb

Allison L Naleway

Padma Koppolu

S Bianca Salas

Lina S Sy

Bruno Lewin

Richard Contreras

Ousseny Zerbo

John R Hansen

Lawrence Block

Karen B Jacobson

Brian E Dixon

Colin Rogerson

Thomas Duszynski

William F Fadel

Michelle A Barron

David Mayer

Catia Chavez

Adam Yates

Lindsey Kirshner

Charlene E McEvoy

Omobosola O Akinsete

Inih J Essien

Tamara Sheffield

Daniel Bride

Julie Arndorfer

Josh Van Otterloo

Karthik Natarajan

Caitlin S Ray

Amanda B Payne

Katherine Adams

Brendan Flannery

Shikha Garg

Abstract

Background

Methods

Results

Conclusions

METHODS

Population and Study Design

Statistical Analysis

RESULTS

Included Population

Influenza Circulation

Pediatric Patient Characteristics

Table 1.

Figure 1.

Pediatric Vaccine Effectiveness

Adult Patient Characteristics

Table 2.

Figure 2.

Adult Vaccine Effectiveness

Vaccine Effectiveness by Time Since Vaccination

Figure 3.

DISCUSSION

Limitations

Conclusions

Supplementary Material

Notes

Contributor Information

Supplementary Data

References

Associated Data

Supplementary Materials

ACTIONS

PERMALINK

RESOURCES