Skip to main content
NCBI home page
JAMA Network logoLink to JAMA Network
. 2023 Feb 2;6(2):e2254387. doi: 10.1001/jamanetworkopen.2022.54387

Rates of and Factors Associated With Primary and Booster COVID-19 Vaccine Receipt by US Veterans, December 2020 to June 2022

Kristina L Bajema 1,2,✉, Mazhgan Rowneki 3, Kristin Berry 4, Amy Bohnert 5,6, C Barrett Bowling 7,8, Edward J Boyko 9, Theodore J Iwashyna 10,11, Matthew L Maciejewski 12,13,14, Ann M O’Hare 15,16, Thomas F Osborne 17,18, Elizabeth M Viglianti 10,19, Denise M Hynes 3,20, George N Ioannou 21,22
PMCID: PMC9896301  PMID: 36729454

Key Points

Question

What was the uptake of and factors associated with COVID-19 primary and booster vaccination in the Veterans Health Administration from December 2020 to June 2022?

Findings

In this cohort study of 5 632 413 enrolled veterans, cumulative incidences were 69.0% for primary vaccination, 42.9% for first booster, and 9.3% for second booster. Older age, Asian or Black race, Hispanic ethnicity, and urban residence were independently associated with receipt of vaccination.

Meaning

These findings suggest targeted outreach to younger, rural veterans may improve COVID-19 vaccination rates.

This cohort study examines factors associated with receipt of COVID-19 vaccination and rates of vaccination among US veterans.

Abstract

Importance

COVID-19 vaccination rates remain suboptimal in the US. Identifying factors associated with vaccination can highlight existing gaps and guide targeted interventions to improve vaccination access and uptake.

Objective

To describe incidence and patient characteristics associated with primary, first booster, and second booster COVID-19 vaccination in the Veterans Health Administration (VHA).

Design, Setting, and Participants

This retrospective cohort study assessed US veterans receiving care in VHA medical centers and outpatient clinics as of December 1, 2020. All VHA enrollees with an inpatient, outpatient, or telehealth encounter in VHA as well as a primary care physician appointment in the preceding 24 months were included.

Exposures

Demographic characteristics, place of residence, prior SARS-CoV-2 infection, and underlying medical conditions.

Main Outcomes and Measures

Cumulative incidence of primary, first booster, and second booster COVID-19 vaccination through June 2022. Cox proportional hazards regression was used to identify factors independently associated with COVID-19 vaccination.

Results

Among 5 632 413 veterans included in the study, 5 094 392 (90.4%) were male, the median (IQR) age was 66 (51-74) years, 1 032 334 (18.3%) were Black, 448 714 (8.0%) were Hispanic, and 4 202 173 (74.6%) were White. Through June 2022, cumulative incidences were 69.0% for primary vaccination, 42.9% for first booster, and 9.3% for second booster. Cumulative incidence for primary vaccination increased with increasing age, from 46.9% (95% CI, 46.8%-47.0%) among veterans aged 18 to 49 years to 82.9% (95% CI, 82.8%-83.0%) among veterans aged 80 to 84 years. More Black veterans completed primary vaccination (71.7%; 95% CI, 71.6%-71.8%) compared with White veterans (68.9%; 95% CI, 68.9%-69.0%), and more urban-dwelling veterans completed primary vaccination (70.9%; 95% CI, 70.9%-71.0%) compared with highly rural-dwelling veterans (63.8%; 95% CI, 63.4%-64.1%). Factors independently associated with higher likelihood of both primary and booster vaccination included older age, female sex, Asian or Black race, Hispanic ethnicity, urban residence, and lack of prior SARS-CoV-2 infection.

Conclusions and Relevance

In this cohort study of US veterans, COVID-19 vaccination coverage through June 2022 was suboptimal. Primary vaccination can be improved among younger, rural-dwelling veterans. Greater uptake of booster vaccination among all veterans is needed.

Introduction

COVID-19 vaccines are highly effective in preventing severe COVID-19 illness and death and have been recommended for everyone 6 months or older in the US.1,2 To date, 4 COVID-19 vaccines have been approved or authorized under US Food and Drug Administration (FDA) Emergency Use Authorization (EUA). The FDA EUA was first issued for the BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) COVID-19 messenger RNA (mRNA) vaccines in December 2020 followed by JNJ-78436735 (Janssen/Johnson & Johnson) in February 2021 and NVX-CoV2373 (Novavax) in July 2022 (eTable 1 in Supplement 1).3 In September 2021, the FDA authorized a booster dose of the Pfizer-BioNTech COVID-19 vaccine in certain populations, with subsequent booster authorization for Moderna and Janssen products in October 2021. Second booster vaccination, first authorized by the FDA in March 2022, was recommended for all adults 50 years or older as well as for persons 12 years or older who were moderately or severely immunocompromised.1,4 After FDA authorization for bivalent formulations of the mRNA vaccines in August 2022, all persons 5 years or older are now recommended to receive bivalent booster vaccination.5

Despite national efforts to encourage COVID-19 vaccination, it is estimated that only approximately 77% of adults in the US had completed primary vaccination by July 2022, of whom only 51% had received a first booster dose.6 Few studies have comprehensively described sociodemographic, geographic, and clinical factors associated with receipt of primary and booster vaccination.7 The Veterans Health Administration (VHA), run by the US Department of Veterans Affairs (VA), provides comprehensive care to more than 9 million enrolled veterans in the US and worked closely with the Centers for Disease Control and Prevention and other federal partners to quickly deliver COVID-19 vaccines to veterans following initial EUA.8 The VHA affords an opportunity to evaluate vaccine uptake in different patient groups and promote equitable access to preventive care. We sought to describe incidence of and factors associated with receipt of COVID-19 primary, first booster, and second booster vaccination among VHA enrollees from December 2020 through June 2022.

Methods

Study Setting and Data Sources

The VHA is the largest integrated health care system in the US, provides care at 171 medical centers and 1113 outpatient clinics throughout the country, and uses a comprehensive nationwide electronic health record (EHR) system.8 We used VA’s Corporate Data Warehouse (CDW), a relational database of VHA enrollees’ EHR data.9 The CDW includes the COVID-19 Shared Data Resource (CSDR), supported by the VA Informatics and Computing Infrastructure, and contains information on all VHA enrollees tested for or vaccinated against COVID-19.10 In addition to vaccines administered through VHA, CSDR captures some COVID-19 vaccines given outside VHA (eg, pharmacies, health departments, mass vaccination centers, and clinics) and electronically reported to VHA or documented by VHA practitioners. To improve ascertainment of vaccination records, information on COVID-19 vaccination was supplemented with the Centers for Medicare & Medicaid Services (CMS) Medicare data for vaccination administered through Medicare services, as well as data from the VA’s Community Care program, which coordinates and reimburses local care provided outside VHA and is accessed through the Patient Integrity Tool.11 For this study, CDW and Patient Integrity Tool data were updated through June 30, 2022, and the CMS Medicare data through December 31, 2021, which represented the most recent date of available CMS Medicare data at the time of analysis. This study was approved by the VA Puget Sound Institutional Review Board, which determined that patient consent was not required. The study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

Study Population

We identified a cohort of veterans 18 years or older enrolled in VHA and alive as of December 1, 2020. We limited the study population to VHA enrollees with an inpatient, outpatient, or telehealth encounter in VHA as well as a primary care physician appointment in the preceding 24 months.

Baseline Characteristics

We ascertained baseline demographic, geographic, and clinical characteristics documented in the 2-year period before the date of cohort entry on December 1, 2020. Race and ethnicity (associated with COVID-19 vaccination) were determined as reported in VHA EHR and enrollment records; other race included self-identification as other or more than 1 race. The latest zip code from the baseline period was used to determine Veterans Integrated Services Networks (VISNs) and rurality of residence based on the Rural-Urban Commuting Areas system.12,13,14 Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared using most recently measured weight and height. We determined the presence of 10 underlying conditions associated with adverse COVID-19–related outcomes (Table) based on International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) codes recorded in the VHA EHR and on VA Community Care service claims.15,16 The ICD-10 codes were also used to calculate the Charlson Comorbidity Index (CCI).17,18 We also determined receipt of immunosuppressive medications or cancer therapies within 2 years before cohort entry.19 To estimate baseline health care use, we ascertained the number of primary care, mental health, and specialty outpatient encounters for each veteran during the 2-year period before cohort entry.20

Table. Cumulative Incidence of COVID-19 Vaccination Among VA Enrollees and aHRs by Demographic, Geographic, and Clinical Factors, December 2020 to June 2022a,b.

Characteristic Veterans in care at the VA, No. (%) Primary vaccination First booster Second booster
No. of events Cumulative incidence, % (95% CI)c aHR (95% CI) (n = 5 632 413) No. of events Cumulative incidence, % (95% CI)c aHR (95% CI) (n = 3 647 739)d No. of events Cumulative incidence, % (95% CI)c aHR (95% CI) (n = 1 937 404)e
Overall 5 632 413 (100) 3 826 436 69.0 (69.0-69.1) 2 320 475 42.9 (42.8-42.9) 497 206 9.3 (9.3-9.4)
Sex
Female 538 021 (9.6) 340 799 63.6 (63.5-63.7) 1.07 (1.06-1.07) 180 516 33.9 (33.8-34.0) 1.09 (1.08-1.09) 34 077 6.4 (6.4-6.5) 1.10 (1.09-1.12)
Male 5 094 392 (90.4) 3 485 637 69.6 (69.6-69.7) 1 [Reference] 2 139 959 43.8 (43.8-43.9) 1 [Reference] 463 129 9.6 (9.6-9.7) 1 [Reference]
Age group, y
18-49 1 327 019 (23.6) 621 623 46.9 (46.8-47.0) 1 [Reference] 208 205 15.7 (15.7-15.8) 1 [Reference] 11 817 0.9 (0.9-0.9) 1 [Reference]f
50-59 807 261 (14.3) 517 004 64.3 (64.2-64.4) 1.54 (1.53-1.54) 269 148 33.7 (33.6-33.8) 1.77 (1.76-1.79) 47 215 5.9 (5.9-6.0) 1.80 (1.72-1.89)
60-69 1 109 186 (19.7) 802 440 73.2 (73.1-73.3) 2.03 (2.02-2.04) 513 886 47.7 (47.6-47.8) 2.59 (2.57-2.6) 121 161 11.4 (11.3-11.4) 2.57 (2.45-2.70)
70-74 1 065 086 (18.9) 836 432 79.8 (79.7-79.9) 2.91 (2.90-2.92) 592 841 58.0 (57.9-58.1) 3.47 (3.45-3.49) 146 324 14.6 (14.5-14.6) 2.85 (2.71-2.98)
75-79 598 366 (10.6) 483 263 82.6 (82.5-82.7) 3.68 (3.67-3.70) 350 411 62.0 (61.9-62.2) 3.73 (3.71-3.75) 87 449 15.8 (15.8-16.0) 2.97 (2.83-3.12)
80-84 307 600 (5.5) 246 221 82.9 (82.8-83.0) 3.94 (3.92-3.96) 175 559 62.4 (62.3-62.6) 3.68 (3.65-3.70) 40 326 14.9 (14.7-15.0) 2.75 (2.62-2.88)
85-89 249 994 (4.4) 196 194 82.8 (82.6-83.0) 4.19 (4.17-4.22) 134 125 61.8 (61.6-62.0) 3.40 (3.37-3.43) 28 206 13.7 (13.6-13.9) 2.42 (2.30-2.54)
≥90 167 901 (3.0) 123 259 80.8 (80.6-81.0) 4.14 (4.12-4.17) 76 300 58.8 (58.5-59.1) 2.87 (2.85-2.9) 14 708 12.5 (12.4-12.7) 2.15 (2.04-2.27)
Race
American Indian or Alaska Native 64 574 (1.1) 39 720 62.4 (62.1-62.8) 0.95 (0.94-0.96) 21 827 35.0 (34.6-35.4) 0.96 (0.95-0.98) 4285 7.0 (6.8-7.2) 0.98 (0.95-1.02)
Asian 80 031 (1.4) 60 113 75.7 (75.4-76.0) 1.48 (1.46-1.49) 36 181 46.0 (45.7-46.4) 1.36 (1.34-1.37) 8403 10.8 (10.5-11.0) 1.47 (1.44-1.51)
Black 1 032 334 (18.3) 730 522 71.7 (71.6-71.8) 1.10 (1.11-1.12) 448 133 44.7 (44.6-44.8) 1.15 (1.14-1.15) 101 301 10.2 (10.1-10.3) 1.24 (1.23-1.25)
Native Hawaiian or Other Pacific Islander 58 643 (1.0) 40 405 69.9 (69.5-70.3) 1.08 (1.07-1.09) 23 864 42.1 (41.7-42.5) 1.04 (1.03-1.06) 5176 9.2 (9.0-9.5) 1.05 (1.02-1.09)
White 4 202 173 (74.6) 2 846 576 68.9 (68.9-69.0) 1 [Reference] 1 741 626 43.3 (43.-43.4) 1 [Reference] 370 444 9.4 (9.3-9.4) 1 [Reference]
Otherg 5900 (0.1) 4701 81.2 (80.2-82.2) 1.10 (1.07-1.13) 3331 59.1 (57.8-60.4) 1.11 (1.07-1.15) 880 15.9 (14.9-16.8) 1.08 (1.00-1.17)
Missing 188 758 (3.4) 104 399 55.6 (55.3-55.8) 1 (0.99-1.00) 45 513 24.3 (24.2-24.5) 0.94 (0.93-0.95) 6717 3.6 (3.5-3.7) 1.08 (1.05-1.11)
Ethnicity
Hispanic or Latino 448 714 (8.0) 313 940 70.8 (70.7-70.9) 1.11 (1.11-1.12) 186 069 42.6 (42.5-42.8) 1.07 (1.06-1.08) 436 669 10.2 (10.1-10.2) 1.11 (1.09-1.12)
Not Hispanic or Latino 4 946 545 (87.8) 3 360 312 69.1 (69.0-69.1) 1 [Reference] 2 047 254 43.1 (43.1-43.2) 1 [Reference] 43 900 9.3 (9.3-9.4) 1 [Reference]
Missing 237 154 (4.2) 152 184 65.3 (65.1-65.5) 0.99 (0.98-0.99) 87 152 38.3 (38.1-38.5) 1.00 (1.00-1.01) 16 637 7.4 (7.3-7.5) 0.95 (0.93-0.96)
Residenceh
Urban 3 771 263 (67.0) 2 632 787 70.9 (70.9-71.0) 1 [Reference] 1 618 052 44.6 (44.5-44.6) 1 [Reference] 363 448 10.2 (10.1-10.2) 1 [Reference]
Rural 1 769 184 (31.4) 1 135 976 65.3 (65.2-65.4) 0.81 (0.81-0.81) 668 246 39.4 (39.4-39.5) 0.84 (0.83-0.84) 126 919 7.6 (7.6-7.6) 0.78 (0.78-0.79)
Highly rural 79 790 (1.4) 49 975 63.8 (63.4-64.1) 0.70 (0.70-0.71) 29 386 38.6 (38.2-38.9) 0.73 (0.72-0.74) 5786 7.7 (7.5-7.9) 0.75 (0.72-0.77)
Missing 12 176 (0.2) 7698 64.3 (63.4-65.2) 0.57 (0.56-0.59) 4791 40.7 (39.8-41.6) 0.77 (0.75-0.80) 1053 9.0 (8.5-9.5) 0.82 (0.76-0.88)
VISN and region
Midwest 1 101 919 (19.6) 758 839 70.0 (69.9-70.1) 1.10 (1.10-1.11) 501 227 47.5 (47.4-47.6) 1.28 (1.28-1.29) 115 189 11.1 (11.1-11.2) 1.43 (1.42-1.45)
10 411 513 (7.3) 269 568 66.7 (66.5-66.8) 0.96 (0.95-0.96) 172 339 43.8 (43.7-44.0) 1.10 (1.09-1.10) 37 418 9.7 (9.6-9.8) 1.10 (1.08-1.11)
12 280 258 (5.0) 201 807 73.2 (73.1-73.4) 1.14 (1.13-1.14) 138 029 51.5 (51.3-51.6) 1.25 (1.25-1.26) 34 893 13.2 (13.1-13.4) 1.44 (1.42-1.46)
15 172 500 (3.06) 110 591 65.2 (65.0-65.4) 0.99 (0.99-1.00) 67 604 40.9 (40.7-41.2) 1.09 (1.08-1.1) 12 489 7.7 (7.6-7.8) 0.98 (0.96-1.01)
23 237 648 (4.2) 176 873 75.5 (75.3-75.7) 1.36 (1.36-1.37) 123 255 54.0(53.8-54.2) 1.48 (1.47-1.49) 30 389 13.6 (13.4-13.7) 1.59 (1.57-1.62)
Northeast 902 660 (16.0) 648 251 73.1 (73.0-73.2) 1.14 (1.13-1.14) 420 880 48.7 (48.6-48.8) 1.22 (1.22-1.23) 94 286 11.1 (11.0-11.2) 1.31 (1.31-1.33)
1 240 609 (4.3) 178 053 75.2 (75.1-75.4) 1.20 (1.20-1.21) 119 125 51.7 (51.5-51.9) 1.25 (1.24-1.26) 29 430 13.0 (12.8-13.1) 1.39 (1.36-1.41)
2 176 961 (3.1) 130 977 75.4 (75.2-75.6) 1.15 (1.14-1.16) 87 241 51.6 (51.3-51.8) 1.18 (1.17-1.19) 20 547 12.4 (12.2-12.5) 1.21 (1.19-1.23)
4 293 900 (5.2) 210 800 73.2 (73.1-73.4) 1.09 (1.09-1.10) 140 448 50.2 (50.0-50.4) 1.18 (1.17-1.18) 29 832 10.9 (10.8-11.0) 1.11 (1.09-1.13)
5 191 190 (3.4) 128 421 68.2 (68.0-68.4) 1.02 (1.01-1.03) 74 066 40.2 (40.0-40.4) 0.98 (0.97-0.99) 14 477 8.0 (7.8-8.1) 0.95 (0.93-0.97)
South 2 291 225 (40.7) 1 506 941 66.8 (66.8-66.9) 1 860 039 39.0 (38.9-39.0) 1 163 804 7.5 (7.5-7.6) 1
6 399 083 (7.1) 264 107 67.2 (67.0-67.3) 1.00 (0.99-1.00) 157 283 40.8 (40.7-41.0) 1.01 (1.00-1.01) 31 471 8.3 (8.2-8.4) 0.95 (0.93-0.96)
7 418 629 (7.4) 278 811 67.7 (67.5-67.8) 1.00 (1.00-1.01) 149 007 36.9 (36.7-37.0) 0.85 (0.85-0.86) 23 909 6.0 (5.9-6.1) 0.70 (0.69-0.71)
8 472 938 (8.4) 325 175 69.8 (69.7-70.0) 1 [Reference] 198 899 43.8 (43.6-43.9) 1 [Reference] 41 902 9.4 (9.3-9.4) 1 [Reference]
9 247 365 (4.4) 154 251 63.4 (63.3-63.6) 0.92 (0.92-0.93) 89 271 37.6 (37.4-37.8) 0.97 (0.96-0.98) 15 245 6.5 (6.4-6.6) 0.79 (0.77-0.81)
16 367 448 (6.5) 231 524 64.1 (63.9-64.2) 0.93 (0.93-0.94) 130 995 37.2 (37.0-37.3) 0.92 (0.92-0.93) 26 049 7.5 (7.4-7.6) 0.95 (0.94-0.97)
17 385 762 (6.9) 253 073 66.5 (66.4-66.7) 1.01 (1.01-1.02) 134 584 36.0 (35.8-36.2) 0.91 (0.90-0.91) 25 228 6.8 (6.7-6.9) 0.89 (0.87-0.90)
West 1 276 997 (22.7) 863 250 68.6 (68.5-68.7) 1.04 (1.04-1.04) 501 960 40.8 (40.7-40.9) 1.04 (1.04-1.05) 112 384 9.3 (9.2-9.3) 1.36 (1.35-1.38)
19 296 814 (5.3) 185 415 63.4 (63.2-63.6) 0.98 (0.97-0.98) 103 511 36.2 (36.0-36.4) 0.98 (0.97-0.98) 21 446 7.6 (7.5-7.7) 1.13 (1.11-1.15)
20 280 117 (5.0) 181 542 65.6 (65.4-65.8) 0.96 (0.95-0.96) 95 271 35.2 (35.1-35.4) 0.85 (0.84-0.86) 17 081 6.4 (6.3-6.5) 0.97 (0.95-0.99)
21 280 148 (5.0) 197 679 71.7 (71.5-71.8) 1.05 (1.04-1.05) 124 631 46.3 (46.1-46.5) 1.06 (1.06-1.07) 31 736 12.0 (11.8-12.1) 1.40 (1.38-1.43)
22 419 918 (7.5) 298 614 72.3 (72.1-72.4) 1.10 (1.09-1.10) 178 547 44.1 (43.9-44.2) 1.04 (1.04-1.05) 42 121 10.5 (10.4-10.6) 1.31 (1.29-1.33)
Missing VISN 59 612 (1.1) 49 155 83.8 (83.5-84.1) 1.11 (1.10-1.12) 36 369 63.5 (63.1-63.9) 1.18 (1.16-1.19) 11 543 20.4 (20.1-20.8) 1.61 (1.57-1.65)
Prior SARS-CoV-2 infectioni
Yes 663 703 (11.8) 431 335 67.1 (67.0-67.2) 0.37 (0.37-0.38) 243 762 39.2 (39.0-39.3) 0.53 (0.53-0.53) 50 560 8.4 (8.3-8.4) 0.73 (0.73-0.74)
No 4 968 710 (88.2) 3 395 101 69.3 (69.3-69.3) 1 [Reference] 2 076 713 43.3 (43.3-43.4) 1 [Reference] 446 646 9.4 (9.4-9.5) 1 [Reference]
BMI
<18.5 47 330 (0.8) 27 986 63.9 (63.5-64.4) 0.76 (0.75-0.77) 14 564 37.0 (36.5-37.4) 0.72 (0.71-0.73) 2926 7.9 (7.6-8.2) 0.83 (0.80-0.87)
18.5 to <25 1 015 185 (18.0) 662 811 67.1 (67.1-67.2) 1 [Reference] 394 528 41.6 (41.5-41.7) 1 [Reference] 84 276 9.1 (9.1-9.2) 1 [Reference]
Overweight 1 982 640 (35.2) 1 366 350 69.9 (69.9-70.0) 1.15 (1.15-1.16) 849 246 44.4 (44.3-44.5) 1.13 (1.13-1.13) 184 691 9.8 (9.8-9.8) 1.05 (1.04-1.06)
Obese I 1 469 359 (26.1) 1 017 008 70.0 (69.9-70.1) 1.20 (1.20-1.21) 622 708 43.6 (43.5-43.6) 1.16 (1.15-1.17) 134 017 9.5 (9.4-9.5) 1.04 (1.03-1.05)
Obese II 646 630 (11.5) 447 579 70.0 (69.9-70.1) 1.22 (1.21-1.22) 269 100 42.8 (42.6-42.9) 1.16 (1.15-1.17) 57 785 9.3 (9.2-9.4) 1.04 (1.03-1.05)
Obese III 329 365 (5.9) 226 983 69.8 (69.7-70.0) 1.19 (1.18-1.19) 133 192 41.8 (41.6-41.9) 1.13 (1.12-1.13) 28 394 9.0 (8.9-9.1) 1.02 (1.00-1.03)
Missing 141 904 (2.5) 77 719 55.6 (55.3-55.9) 1.08 (1.07-1.08) 37 137 27.1 (26.8-27.3) 1.05 (1.04-1.06) 5117 3.8 (3.7-3.9) 1.02 (0.99-1.06)
CCI
0 2 789 879 (49.5) 1 688 972 60.9 (60.8-61.0) 1 [Reference] 915 219 33.3 (33.2-33.4) 1 [Reference] 161 466 5.9 (5.9-5.9) 1 [Reference]
1 1 143 086 (20.3) 821 942 73.0 (72.9-73.1) 1.06 (1.06-1.06) 514 588 46.7 (46.6-46.8) 1.00 (1.00-1.00) 109 109 10.1 (10.0-10.1) 1.00 (0.99-1.01)
2 754 978 (13.4) 576 861 78.0 (77.9-78.1) 1.08 (1.08-1.08) 386 492 53.9 (53.8-54.0) 0.99 (0.99-1.00) 91 813 13.2 (13.0-13.2) 1.01 (1.00-1.02)
3 376 787 (6.7) 294 154 80.5 (80.4-80.7) 1.08 (1.07-1.08) 200 266 57.5 (57.3-57.6) 0.95 (0.94-0.95) 50 924 15.1 (15.0-15.2) 1 (0.98-1.01)
4 238 746 (4.2) 189 173 82.3 (82.1-82.5) 1.09 (1.08-1.09) 130 662 60.2 (60.0-60.4) 0.93 (0.92-0.93) 34 254 16.4 (16.2-16.6) 0.98 (0.97-0.99)
≥5 328 937 (5.8) 255 334 83.0 (82.9-83.2) 1.09 (1.08-1.09) 173 248 61.9 (61.8-62.1) 0.85 (0.85-0.86) 49 640 18.8 (18.7-19.0) 0.98 (0.98-1.00)
Chronic kidney disease
No 5 068 252 (90.0) 3 388 889 67.7 (67.7-67.8) 1 [Reference] 2 025 245 41.3 (41.2-41.3) 1 [Reference] 422 803 8.7 (8.7-8.8) 1 [Reference]
Yes 564 161 (10.0) 437 547 81.1 (81.0-81.2) 1.02 (1.02-1.03) 295 230 58.5 (58.3-58.6) 0.93 (0.93-0.93) 74 403 15.4 (15.3-15.5) 0.96 (0.96-0.97)
COPD
No 4 918 208 (87.3) 3 293 278 67.8 (67.8-67.9) 1 [Reference] 1 972 590 41.4 (41.4-41.4) 1 [Reference] 411 103 8.7 (8.7-8.8) 1 [Reference]
Yes 714 205 (12.7) 533 158 77.6 (77.4-77.6) 0.98 (0.98-0.98) 347 885 53.6 (53.5-53.7) 0.90 (0.90-0.91) 86 103 13.8 (13.7-13.9) 0.98 (0.97-0.98)
Congestive heart failure
No 5 387 941 (95.7) 3 642 782 68.6 (68.5-68.6) 1 [Reference] 2 201 168 42.3 (42.2-42.3) 1 [Reference] 465 301 9.1 (9.0-9.1) 1 [Reference]
Yes 244 472 (4.3) 183 654 80.2 (80.0-80.3) 0.93 (0.92-0.93) 119 307 57.3 (57.1-57.5) 0.83 (0.83-0.84) 31 905 16.3 (16.1-16.4) 0.95 (0.94-0.96)
Diabetes
No 4 111 824 (73.0) 2 652 405 65.3 (65.3-65.4) 1 [Reference] 1 531 972 38.4 (38.4-38.5) 1 [Reference] 304 523 7.7 (7.7-7.8) 1 [Reference]
Yes 1 520 589 (27.0) 1 174 031 79.2 (79.1-79.3) 1.06 (1.06-1.06) 788 503 55.2 (55.1-55.3) 1.00 (1.00-1.00) 192 683 13.8 (13.8-13.9) 1.00 (0.99-1.01)
Obstructive sleep apnea
No 4 327 550 (76.8) 2 877 786 67.6 (67.6-67.7) 1 [Reference] 1 726 508 41.6 (41.6-41.67 1 [Reference] 355 240 8.7 (8.7-8.7) 1 [Reference]
Yes 1 304 863 (23.2) 948 650 73.6 (73.6-73.7) 1.15 (1.15-1.16) 593 967 47.0 (46.9-47.0) 1.11 (1.11-1.11) 141 966 11.4 (11.3-11.4) 1.07 (1.06-1.08)
Peripheral arterial disease
No 5 277 070 (93.7) 3 553 728 68.3 (68.3-68.4) 1 [Reference] 2 137 565 41.9 (41.9-42.0) 1 [Reference] 448 509 8.9 (8.9-8.9) 1 [Reference]
Yes 355 343 (6.3) 272 708 80.3 (80.1-80.4) 1.01 (1.01-1.02) 182 910 57.6 (57.4-57.8) 1.02 (1.02-1.03) 48 697 16.0 (15.9-16.2) 1.01 (1-1.02)
Venous thromboembolism
No 5 543 831 (98.4) 3 761 526 68.9 (68.9-69.0) 1 [Reference] 2 277 722 42.7 (42.7-42.8) 1 [Reference] 485 695 9.2 (9.2-9.3) 1 [Reference]
Yes 88 582 (1.6) 64 910 76.5 (76.2-76.8) 0.95 (0.94-0.95) 42 753 53.3 (53.0-53.7) 0.93 (0.92-0.94) 11 511 14.9 (14.6-15.1) 0.98 (0.96-1.00)
Bipolar disorder or schizophrenia
No 5 393 119 (95.8) 3 669 964 69.2 (69.1-69.2) 1 [Reference] 2 231 558 43.1 (43.0-43.1) 1 [Reference] 477 010 9.3 (9.3-9.4) 1 [Reference]
Yes 239 294 (4.6) 156 472 66.5 (66.3-66.6) 0.95 (0.94-0.95) 88 917 38.6 (38.4-38.8) 0.96 (0.95-0.96) 20 196 8.9 (8.8-9.0) 1.01 (1.00-1.03)
Major depressive disorder
No 4 224 815 (75.0) 2 894 245 69.6 (69.6-69.7) 1 [Reference] 1 787 368 44.1 (44.0-44.1) 1 [Reference] 380 116 9.5 (9.5-9.6) 1 [Reference]
Yes 1 407 598 (25.0) 932 191 67.2 (67.1-67.3) 1.01 (1.01-1.02) 533 107 39.2 (39.1-39.3) 0.98 (0.97-0.98) 117 090 8.7 (8.7-8.8) 0.95 (0.95-0.96)
PTSD
No 4 492 979 (79.8) 3 094 092 70.1 (70.0-70.1) 1 [Reference] 1 907 042 44.3 (44.3-44.4) 1 [Reference] 406 570 9.6 (9.6-9.6) 1 [Reference]
Yes 1 139 434 (20.2) 732 344 64.9 (64.8-65.0) 1.01 (1.01-1.02) 413 433 37.1 (37.0-37.2) 1.02 (1.02-1.03) 90 636 8.2 (8.2-8.3) 1.01 (1.00-1.02)
No. of primary care visits in prior 2 y
1-5 2 237 618 (39.7) 1 369 267 62.0 (62.0-62.1) 1 [Reference] 770 084 35.6 (35.5-35.6) 1 [Reference] 123 562 5.8 (5.7-5.8) 1 [Reference]
6-11 1 645 868 (29.2) 1 150 906 70.8 (70.8-70.9) 1.11 (1.10-1.11) 701 331 44.0 (43.9-44.1) 1.04 (1.03-1.04) 149 932 9.5 (9.5-9.6) 1.23 (1.21-1.24)
≥12 1 748 927 (31.1) 1 306 263 76.4 (76.3-76.4) 1.10 (1.10-1.11) 849 060 51.3 (51.2-51.4) 1.02 (1.02-1.03) 223 712 13.8 (13.7-13.8) 1.27 (1.25-1.29)
No. of mental health visits in prior 2 y
0 3 686 303 (65.5) 2 559 581 70.7 (70.6-70.7) 1 [Reference] 1 599 327 45.3 (45.3-45.4) 1 [Reference] 334 926 9.6 (9.6-9.7) 1 [Reference]
1-6 971 390 (17.3) 615 048 64.3 (64.2-64.4) 0.94 (0.93-0.94) 343 520 36.7 (36.6-36.8) 0.93 (0.92-0.93) 75 149 8.1 (8.1-8.2) 1.00 (0.99-1.01)
7-19 588 785 (10.5) 391 919 67.3 (67.2-67.4) 1.01 (1.01-1.01) 225 537 39.3 (39.2-39.4) 0.99 (0.98-0.99) 51 017 9.0 (8.9-9.1) 1.05 (1.04-1.06)
≥20 385 935 (6.9) 259 888 68.1 (68.0-68.3) 1.01 (1.00-1.01) 152 091 40.5 (40.4-40.7) 1.00 (1.00-1.01) 36 114 9.7 (9.6-9.8) 1.11 (1.09-1.12)
No. of specialty care visits in prior 2 y
0 292 113 (5.2) 149 714 52.0 (51.9-52.2) 1 [Reference] 75 881 26.9 (26.8-27.1) 1 [Reference] 138 739 3.4 (3.4-3.5) 1 [Reference]
1-5 2 447 383 (43.5) 1 526 760 63.2 (63.2-63.3) 1.27 (1.26-1.29) 851 507 36.0 (35.9-36.0) 1.10 (1.09-1.11) 111 878 5.9 (5.9-6.0) 1.35 (1.31-1.38)
6-10 1 249 089 (22.2) 880 476 71.5 (71.4-71.6) 1.42 (1.41-1.43) 533 647 44.2 (44.1-44.3) 1.19 (1.18-1.20) 126 805 9.4 (9.3-9.4) 1.7 (1.66-1.75)
11-20 1 017 444 (18.1) 767 201 76.7 (76.6-76.8) 1.54 (1.53-1.55) 502 969 51.5 (51.4-51.6) 1.30 (1.29-1.3) 110 211 13.2 (13.1-13.3) 2.02 (1.96-2.07)
≥21 626 384 (11.1) 502 285 82.6 (82.6-82.8) 1.76 (1.75-1.77) 356 471 61.4 (61.2-61.5) 1.45 (1.43-1.46) 138 739 19.6 (19.4-19.6) 2.45 (2.39-2.52)
Open in a new tab

Abbreviations: aHR, adjusted hazard ratio; BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); CCI, Charlson Comorbidity Index; COPD, chronic obstructive pulmonary disease; PTSD, posttraumatic stress disorder; VA, Department of Veterans Affairs; VISN, VA Integrated Service Network.

a

Veterans 18 years or older with an inpatient, outpatient, or telehealth encounter, including a primary care visit, in the VA health care system in the 24 months preceding cohort entry on December 1, 2020.

b

Adjusted for sex, age, race, ethnicity, urban vs rural residence, VISN, SARS-CoV-2 infection, BMI, CCI, number of primary care visits in 2 years before December 1, 2020, number of mental health visits in prior 2 years, and number of specialty care visits in prior 2 years.

c

Cumulative incidence among entire cohort.

d

Includes veterans who completed primary vaccination and obtained a first booster dose on or after September 22, 2021.

e

Includes veterans 50 years or older as of March 2022 who completed first booster vaccination and obtained a second booster dose on or after March 29, 2022.

f

Reference group for second booster includes veterans aged 18 to 49 years at the start of the study period in December 2020 who were 50 years or older as of March 2022 when second booster vaccination received US Food and Drug Administration Emergency Use Authorization.

g

Other race includes veterans who self-identified their race as other or who self-identified as belonging to more than 1 race category.

h

Based on Rural-Urban Commuting Area codes.

i

SARS-CoV-2 infection diagnosed before or on the date of completion of COVID-19 primary, first booster, second booster vaccination, or last day of observation period.

COVID-19 Vaccination Definitions

We aggregated all administered vaccine doses documented in the CDW, CMS Medicare, and VA Community Care records. Vaccine records with service dates before December 11, 2020, the earliest date of EUA for COVID-19 vaccination in the US, were excluded. To ensure that vaccine doses documented in more than 1 source were not counted more than once, after combining records from all sources, we treated 2 vaccine doses as duplicates if they were documented as having been received within 7 days of each other.

We included mRNA-1273 (52% of all vaccine doses), BNT162b2 (45%), and JNJ-78436735 (3%) vaccine types, which were approved in the US during the period of study and comprised most of all vaccine types. To allow for complete ascertainment of vaccination in VHA, we also included AZD1222 (Oxford-AstraZeneca) (0.01%) and NVX-CoV2373 (<0.01%, authorized after the end of this study period). Vaccine doses of unknown or other type (0.01%) were excluded from the analysis.

Beginning December 1, 2020, we determined the time to completion of the following vaccination end points, with follow-up extending through June 30, 2022. Primary vaccination was indicated by receipt of 2 doses of mRNA (BNT162b2 or mRNA-1273), a single dose of JNJ-78436735, 2 doses of NVX-CoV2373, or 2 doses of AZD1222 COVID-19 vaccine. First booster vaccination was indicated by any primary vaccination regimen above, followed by an additional dose of mRNA, JNJ-78436735, NVX-CoV2373, or AZD1222 vaccine. Second booster vaccination was indicated by any first booster vaccination above, followed by an additional dose of mRNA, JNJ-78436735, NVX-CoV2373, or AZD1222 vaccine.

Heterologous vaccination (use of different vaccine products) was allowed for determination of primary and booster vaccination. Prior SARS-CoV-2 infection was based on the earlier of either first laboratory-confirmed SARS-CoV-2 test in CSDR or first COVID-19 diagnosis date in CMS Medicare data and ascertained as of the date of primary or booster vaccination completion.

Statistical Analysis

Descriptive statistics were generated for patients receiving primary and booster vaccination. Kaplan-Meier curves were used to compare cumulative incidence of vaccination by selected characteristics. Sensitivity analysis was conducted from December 1, 2020, through December 31, ,2021 comparing VA data sources alone and combined VA and CMS Medicare data.

Cox proportional hazards regression was used to identify factors independently associated with time to primary and booster vaccination after adjusting for sex, age, race, ethnicity, urban vs rural residence, VISN, SARS-CoV-2 infection (modeled as a time-varying covariate), BMI, CCI, and number of primary care, mental health, or specialty care visits in the prior 2 years. We did not adjust for CCI when evaluating individual conditions to avoid overadjustment because the CCI quantifies numerous underlying conditions. Time-to-event analyses were censored on June 30, 2022, or at the time of death if earlier.

For primary vaccination, time-to-event Cox proportional hazards regression analyses began on December 11, 2020, and were conducted among all eligible cohort members. For first booster vaccination, time-to-event analyses began on September 22, 2021, when the FDA authorized a booster dose of the BNT162b2 COVID-19 vaccine, and were limited to cohort members who had completed primary vaccination.3 For second booster vaccination, time-to-event analyses began on March 29, 2022, when the FDA authorized a second booster vaccination, and were limited to cohort members 50 years or older as of March 2022 who had received a first booster. Cox proportional hazards regression analyses were limited to persons who were alive and had not yet experienced the vaccination outcome of interest as of the first day of follow-up. The proportional hazards assumption was tested using log-log plot and Schoenfeld residuals. Cumulative incidence and HRs were compared using 95% CIs. Analyses were conducted in Stata software, version 17 (StataCorp LLC).

Results

Cohort Characteristics

We identified 8 822 259 persons 18 years or older who were enrolled in VHA and alive as of December 1, 2020. We excluded 2 455 835 veterans (27.8%) without any inpatient, outpatient, or telehealth encounters in the preceding 24 months as well as an additional 734 011 veterans (8.3%) without primary care visits during the same period. Among the 5 632 413 veterans included in the study, 5 094 392 (90.4%) were male and 538 021 (9.6%) were female; the median (IQR) age was 66 (51-74) years; 64 574 (1.1%) were American Indian or Alaska Native, 80 031 (1.4%) were Asian, 1 032 334 (18.3%) were Black, 58 643 (1.0%) were Native Hawaiian or other Pacific Islander, 4 202 173 (74.6%) were White, 5900 (0.1%) were of other race, and 188 758 (3.4%) were missing race; 448 714 (8.0%) were Hispanic or Latino, 4 946 545 (87.8%) were not Hispanic or Lationo, and 237 154 (4.2%) were missing ethnicity (Table). The median (IQR) CCI was 1 (0-2), and 300 359 veterans (5.3%) had received immunosuppressive medications or cancer treatments. A total of 2 445 354 veterans (43.4%) had obesity, 1 520 589 (30.2%) had diabetes, 714 205 (12.7%) had chronic obstructive pulmonary disease (COPD), and 564 161 (10.0%) had chronic kidney disease.

Cumulative Incidence of Vaccination

By June 30, 2022, a total of 32.1% of veterans were unvaccinated, 26.7% had completed primary vaccination only (no booster), and 41.2% had completed booster vaccination (Figure 1); among veterans aged 18 to 49 years, 54.0% were unvaccinated and 31.1% had completed primary vaccination only. Cumulative vaccination incidences were 69.0% for primary vaccination, 42.9% for first booster, and 9.3% for second booster (Table). Cumulative incidence for primary vaccination increased with age and was 46.9% (95% CI, 46.8%-47.0%) among veterans aged 18 to 49 years, 73.2% (95% CI, 73.1%-73.3%) among veterans aged 60 to 69 years, and 82.9% (95% CI, 82.8%-83.0%) among veterans aged 80-84 years (Table and Figure 2); similarly, for a first booster it increased from 15.7% (95% CI, 15.7%-15.8%) among veterans aged 18 to 49 years to 47.7% (95% CI, 47.6%-47.8%) among veterans aged 60 to 69 years to 62.4% (95% CI, 62.3%-62.6%) among veterans aged 80-84 years and for a second booster from 11.4% (95% CI, 11.3%-11.4%) among veterans aged 60 to 69 years to 14.9% (95% CI, 14.7%-15.0%) for veterans aged 80 to 84 years (Table, Figure 3 and Figure 4).

Figure 1. Percentage of US Veterans With No Receipt and Receipt of Primary and Booster Vaccination for COVID-19 as of June 30, 2022, Overall and by Age Group.

Figure 1.

Open in a new tab

Age was determined in March 2022, when the US Food and Drug Administration authorized a second booster vaccination for persons 50 years or older.

Figure 2. Cumulative Incidence of COVID-19 Primary Vaccination Among US Veterans, December 1, 2020, to June 30, 2022.

Figure 2.

Open in a new tab

Figure 3. Cumulative Incidence of COVID-19 First Booster Vaccination Among US Veterans, September 1, 2021, to June 30, 2022.

Figure 3.

Open in a new tab

Figure 4. Cumulative Incidence of COVID-19 Second Booster Vaccination Among US Veterans, March 1, 2022, to June 30, 2022.

Figure 4.

Open in a new tab

More veterans of Black race completed primary vaccination (71.7%; 95% CI, 71.6%-71.8%) compared with White veterans (68.9%; 95% CI, 68.9%-69.0%). Completion of primary vaccination was also higher among Asian compared with White veterans (75.7%; 95% CI, 75.4%-76.0%). Incidence was lowest among American Indian and Alaska Native groups (primary vaccination: 62.4%; 95% CI, 62.1%-62.8%).

Cumulative incidence of primary and booster vaccination was higher among veterans who had not experienced prior SARS-CoV-2 infection. Incidence increased with higher CCI; cumulative incidences for primary vaccination were 60.9% for veterans with a CCI of 0, 73.0% for those with a CCI of 1, 78.0% for a CCI of 2, and 83.0% for a CCI of 5 or higher; for first booster vaccination, 33.3%, 46.7%, 53.9%, and 61.9%, respectively; and for second booster vaccination, 5.9%, 10.1%, 13.1%, and 18.9%, respectively. Cumulative incidence of primary, first booster, and second booster vaccination was higher for veterans with conditions such as diabetes, chronic kidney disease, and COPD compared with those without the respective conditions but lower for mental health conditions, including major depressive disorder, posttraumatic stress disorder, and bipolar disorder or schizophrenia (Table). Cumulative incidence of vaccination was also higher for veterans with higher numbers of primary and specialty care visits (eFigure in Supplement 1). The absolute increase in incidence with the addition of CMS Medicare data was small (eTable 2 in Supplement 1).

Factors Associated With Vaccination

Adjusting for demographic, clinical, and geographic characteristics (Table), vaccination was more likely among older age groups (for age 80-84 years vs 18-49 years, primary adjusted hazard ratio [aHR], 3.94; 95% CI, 3.92-3.96; first booster aHR, 3.68; 95% CI, 3.65-3.70; second booster aHR, 2.75; 95% CI, 2.62-2.88) and women (vs men, primary aHR, 1.07; 95% CI, 1.06-1.07; first booster aHR, 1.09; 95% CI, 1.08-1.09; second booster aHR, 1.10; 95% CI, 1.09-1.12). Black veterans were more likely than White veterans to receive vaccination (primary aHR, 1.10; 95% CI, 1.11-1.12; first booster aHR, 1.15; 95% CI, 1.14-1.15; second booster aHR, 1.24; 95% CI, 1.23-1.25), as were Asian persons (primary aHR, 1.48; 95% CI, 1.46-1.49; first booster aHR, 1.36; 95% CI, 1.34-1.37; second booster aHR, 1.47; 95% CI, 1.44-1.51) and Hispanic compared with non-Hispanic veterans (primary aHR, 1.11; 95% CI, 1.11-1.12; first booster aHR, 1.07; 95% CI, 1.06-1.08; second booster aHR, 1.11; 95% CI, 1.09-1.12). American Indian and Alaska Native groups were less likely to receive vaccination compared with White veterans (primary aHR, 0.95; 95% CI, 0.94-0.96; first booster aHR, 0.96; 95% CI, 0.95-0.98).

Veterans living in highly rural areas were less likely (63.8%; 95% CI, 63.4%-64.1%) to complete vaccination than urban veterans (primary aHR, 0.70; 95% CI, 0.70-0.71 highly rural; aHR, 0.81; 95% CI, 0.81-0.81 rural). Persons experiencing prior SARS-CoV-2 infection were less likely to receive any vaccination (primary aHR, 0.37; 95% CI, 0.37-0.38; first booster aHR, 0.53; 95% CI, 0.53-0.53; second booster aHR, 0.73; 95% CI, 0.73-0.74).

Veterans with higher CCIs (≥5 vs 0) were more likely to have primary vaccination (aHR, 1.09; 95% CI, 1.08-1.09) but less likely to have a first booster (aHR, 0.85; 95% CI, 0.85-0.86). Likelihood of primary vaccination also varied by individual underlying condition (diabetes: aHR, 1.06; 95% CI, 1.06-1.06; COPD: aHR, 0.98; 95% CI, 0.98-0.98). Higher numbers of baseline primary and specialty care encounters were also associated with primary vaccination (≥12 vs 1-5 primary care visits: aHR, 1.10; 95% CI, 1.10-1.11; ≥21 vs no specialty care visits: aHR, 1.76; 95% CI, 1.75-1.77).

Discussion

In this nationwide study of 5.6 million US veterans receiving VHA care as of December 2020, the cumulative vaccination incidences through June 2022 were 69.0% for primary vaccination, 42.9% for first booster, and 9.3% for second booster. Incidence was lowest among the youngest veterans (aged 18-49 years), with 46.9% receiving primary vaccination and 15.7% receiving first booster vaccination compared with older groups (82.9% receiving primary vaccination and 62.4% receiving first booster vaccination among veterans aged 80-84 years). Incidence was also higher among veterans living in urban compared with rural areas. There was geographic variability in incidence of vaccination across VA VISNs. Accounting for demographic, clinical, and geographic differences, likelihood of primary and booster vaccination was also much higher among older veterans as well as women; Asian, Black, and Hispanic groups; and residents of urban areas.

Although COVID-19 vaccines have been demonstrated to be safe and effective, rates of vaccination across the US remain suboptimal, and booster vaccination lags well behind primary vaccination despite being broadly recommended.2,6,21,22 Although national-level surveillance provides data on demographic and geographic trends, a more complete picture that includes important clinical factors is important to informing strategies to improve vaccination access and uptake. In this study, we present the most comprehensive, longitudinal assessment of COVID-19 vaccination across VHA to date and incorporate detailed background on demographic, geographic, and clinical factors, including health care use and underlying conditions.

As observed in the general US population, compared with older veterans, we found that uptake of vaccination among younger veterans has remained lower.6 More than half (54.0%) of veterans in care aged 18 to 49 years were unvaccinated, whereas 31.1% had completed primary vaccination only. Even among veterans aged 50 to 69 years, incidence was still significantly lower than in older groups. Differences in risk perception of SARS-CoV-2 infection and related outcomes, vaccine safety and efficacy, and trust in authorities may contribute to a lower incidence and likelihood of vaccination among younger groups.23

Notable differences were seen in vaccination by racial and ethnic groups, with higher incidence among Asian, Black, and Hispanic veterans compared with White and non-Hispanic groups. Following observation of early disparities in vaccination coverage among US racial and ethnic minorities, efforts to provide equitable vaccine access were undertaken to reduce this gap.7 In VHA, during the early months after initial COVID-19 vaccine EUA, vaccination coverage was higher among Black and Hispanic veterans compared with non-Hispanic White veterans.24 Equal access to comprehensive VHA health care and targeted outreach mitigates some racial and ethnic disparities.25 Consistent with a previous study,7 we found that incidence of vaccination has remained lower for American Indian and Alaska Native groups. This finding is particularly concerning because American Indian and Alaska Native persons have been disproportionately affected by COVID-19, including higher rates of illness, hospitalization, and death.26,27 Continued support and targeted outreach for COVID-19 vaccination within VHA remain important to reduce these disparities.

Differences in COVID-19 vaccination by rurality were also observed, with veterans in urban areas more likely to complete primary and booster vaccination. Although the cumulative incidence of primary and first booster vaccination in this study was 5% higher among urban residents, this difference is smaller than in nonveteran populations, where the gap has increased significantly over time.28 Possible reasons for observed differences include dedicated programmatic efforts to provide care to rural veterans as well as the role of VHA and VHA practitioners as trusted sources of vaccine information.29,30

After adjusting for demographic, clinical, and geographic characteristics, persons with a greater burden of underlying medical conditions, as measured by the CCI, had a slightly higher likelihood of primary vaccination but slightly lower likelihood of booster vaccination. In contrast, an earlier VA study24 found that the likelihood of vaccination during the first 3 months following COVID-19 vaccine EUA increased significantly among persons with higher CCIs. Although early vaccination efforts prioritized persons at highest risk for severe COVID-19 outcomes, these results indicate that, over time, higher-risk patients may have less impetus for receiving COVID-19 vaccination, despite their increased risk of severe COVID-19 outcomes.31

Limitations

This study has several limitations. First, although we restricted the study population to veterans engaged in care and integrated multiple data sources to strengthen ascertainment of COVID-19 vaccination, we likely did not fully capture all vaccinations received outside VHA. In addition, CMS Medicare vaccination data only extended to December 31, 2021; however, we demonstrated in sensitivity analysis that the overall absolute increase in vaccination uptake with the addition of these data was relatively small. Underascertainment of vaccination is likely to be more pronounced for booster vaccination because vaccines have become more broadly accessible in the community over time. Although the absolute vaccination rates that we report underestimate slightly the true vaccination rates of VHA enrollees, the associations and trends of different vaccination factors are likely to be consistent. Second, we did not specify primary vaccination separately for immunocompromised persons, for whom additional vaccine doses are recommend32; however, overall misclassification of primary vs booster vaccination in this study is expected to be low given the relatively low prevalence in the cohort. Third, our definitions of primary and booster vaccination did not require prespecified intervals between doses,2 which may have resulted in a small degree of overascertainment of vaccination completion. In a prior VA study,24 we demonstrated that a second mRNA vaccine dose was administered within 4 days of the recommended date in 95% of cases for both BNT162b2and mRNA-1273, demonstrating excellent dosing adherence. On the other hand, we considered as duplicates any 2 vaccine doses administered within 7 days of each other, whereas other estimates did not apply this criterion.6 Comparisons of vaccination coverage reported in VA vs non-VA studies must therefore be interpreted with caution.

Conclusions

In this retrospective cohort study of US veterans receiving VHA care, uptake of COVID-19 primary and booster vaccination remained underused, similar to trends observed in the general US population. Several important demographic and clinical factors were associated with vaccination. Younger, rural, American Indian and Alaska Native groups, and persons with a high burden of underlying conditions may benefit from targeted outreach to improve COVID-19 vaccination rates.

Supplement 1.

eTable 1. Key Relevant COVID-19 Vaccine U.S. Food and Drug Administration Emergency Use Authorization Dates, December 2020-March 2022

eTable 2. Cumulative Incidence of COVID-19 Primary and First Booster Vaccination Among VA Enrolleesa Based on VA Data Sourcesb vs VA Data Combined With CMS-Medicare Data Sources, December 2020-December 2021

eFigure. Cumulative Incidence of COVID-19 Primary Vaccination (A-B), First Booster (C-D), and Second Booster Vaccination (E-F) Among U.S. Veterans by Number of Primary and Specialty Care Visits in the Prior 2 Years, December 1, 2020-June 30, 2022

Click here for additional data file. (545.3KB, pdf)
Supplement 2.

Data Sharing Statement

Click here for additional data file. (14KB, pdf)

References

Associated Data

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

Supplementary Materials

Supplement 1.

eTable 1. Key Relevant COVID-19 Vaccine U.S. Food and Drug Administration Emergency Use Authorization Dates, December 2020-March 2022

eTable 2. Cumulative Incidence of COVID-19 Primary and First Booster Vaccination Among VA Enrolleesa Based on VA Data Sourcesb vs VA Data Combined With CMS-Medicare Data Sources, December 2020-December 2021

eFigure. Cumulative Incidence of COVID-19 Primary Vaccination (A-B), First Booster (C-D), and Second Booster Vaccination (E-F) Among U.S. Veterans by Number of Primary and Specialty Care Visits in the Prior 2 Years, December 1, 2020-June 30, 2022

Click here for additional data file. (545.3KB, pdf)
Supplement 2.

Data Sharing Statement

Click here for additional data file. (14KB, pdf)

Articles from JAMA Network Open are provided here courtesy of American Medical Association

RESOURCES