Respiratory Syncytial Virus Infection in Older Adults in Asia: A Modified Delphi Expert Consensus on Surveillance, Diagnosis, and Prevention

Abstract

Introduction

Respiratory syncytial virus (RSV) is a public health concern, particularly among neonates/young infants, in individuals with chronic medical conditions, and for older adults. In contrast to children, limits in surveillance and substantial underreporting obscure the full impact of RSV infections on adults. A structured process for adult RSV disease decision-making can guide public health epidemiology and planning.

Methods

Twelve experts from six Asian countries (Indonesia, Malaysia, Philippines, Singapore, Taiwan, and Thailand) participated in a modified Delphi consensus study to guide surveillance, diagnosis, and impact of RSV in adults in Asia. The expert recommendations could be organized into four themes: epidemiology and surveillance, diagnosis, high-risk groups, and healthcare utilization.

Results

The expert panel recommended strengthening RSV disease monitoring through integration within current influenza and COVID-19 surveillance systems. Furthermore, to standardize RSV case definitions, it was recommended that the RSV respiratory infection clinical criteria exclude fever. Although rapid antigen tests are employed as standard of care, polymerase chain reaction (PCR) testing should be utilized whenever feasible. Along with year-round testing in Asia to establish incidence, an adjustment factor of at least 2.2-fold was recommended to address the underestimation of RSV-related hospitalization rates based on single-specimen PCR testing. For all adults aged ≥ 75 as well as for those adults aged ≥ 60 with comorbid or immunocompromising conditions, or those residing in long-term care facilities, the experts recommended universal RSV vaccination (contingent upon vaccine licensure), and cost-effectiveness analyses should be used to inform region-specific policy decisions.

Conclusions

Priority actions proposed for adult RSV infection and disease include streamlining diagnostic testing processes, launching disease awareness campaigns, and engaging public health authorities to advance prevention programs in coordinated efforts with policymakers and payers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41030-025-00321-2.

Key Summary Points

RSV infection poses a threat to older adults’ health, with substantial hospital admission rates and imposing economic burdens on healthcare systems.

In older adults, limited surveillance and clinical underdiagnosis hinder a complete understanding of RSV disease frequency.

This study of RSV disease in Asia applies the modified Delphi expert consensus method to establish recommendations to guide surveillance, clinical decision-making, and public health strategies.

A panel of 12 Asia-based experts provided recommendations about RSV in older adults, spanning from epidemiology and surveillance, diagnostic strategies, and vaccination prioritization, to the economic impact.

Delphi study recommendations include conducting year-round RSV detection, integrating RSV monitoring with existing influenza and COVID-19 surveillance systems, revising case definitions to remove the fever criteria for RSV respiratory infections, prioritizing (where possible) PCR-based testing, recommending universal vaccination (upon licensure) for older populations ≥ 75 years and for adults ≥ 60 years with certain risk factors, and performing cost-effectiveness analyses to inform policy decisions.

Introduction

Respiratory syncytial virus (RSV) infection in older adults, although often underrecognized, is responsible for considerable challenges to the healthcare system like elevated hospitalization rates [1, 2]. In economically developed nations, the annual population-based incidence of RSV disease among older adults, without adjustment to account for potential underestimation, is approximately 1% (600.7 cases per 100,000 person-years), with about one in four cases being hospitalized (i.e., hospitalization rates around 157 per 100,000 person-years) [1, 3]. Comparing older adults aged 70 years and above to children younger than 5 years, the worldwide age-specific mortality rate ratio has tripled from 0.57 in 1990 to 1.85 in 2019 [4].

RSV is categorized on the basis of surface protein variability into two subgroups, RSV-A and RSV-B, that co-circulate. Although subgroup predominance fluctuates by season, there appears to be no substantial difference between RSV-A and RSV-B in clinical presentation or severity [5–8]. In Asia, for instance, RSV infections in older adults remain substantially underreported despite the fact that these can lead to a complicated clinical course, particularly among patients with comorbidities [2]. Severe RSV infections demand hospital resources, as exemplified by the need for supplemental oxygen or mechanical ventilation and by extended hospital and intensive care unit stays [2]. Surveillance protocols and systematic data collection for elderly patients or other high-risk adult patients are available from a few countries in Asia, such as China, Japan, Singapore, and South Korea, and most other nations lack adequate surveillance systems [2, 9–13]. Japan initiated its RSV surveillance program in 2003; South Korea launched the KINRESS (Korean Influenza and Respiratory Virus Surveillance System) in 2005, which monitors major respiratory viruses across uniformly distributed sentinel sites [13]. There are hospital-based studies in older adults published from Hong Kong and Thailand [10]. Economic burden analyses for RSV disease in older adults in Asia are limited [14]. Integrating RSV surveillance with established influenza (and potentially COVID-19) monitoring systems has been shown to be beneficial, as it leverages existing infrastructure to broaden infectious disease tracking with minimal additional cost and effort [15].

Previous initiatives, such as the PROUD Taskforce (Preventing RespiratOry syncytial virUs in unDerdeveloped countries), which brought together 24 RSV global experts, have identified key gaps in low- and middle-income countries (LMICs) for RSV diagnostics, clinical and public education, access to future vaccines and novel interventions that is prompt and affordable, and policy engagement [16]. These insights, along with the substantial clinical challenge of older adult disease on the healthcare system [2, 9], highlight the need for guidance in the diagnosis and management of RSV infections that can provide essential baseline groundwork in anticipation of future vaccine introductions [12, 17, 18].

A panel of experts from six Asian countries was assembled to establish consensus towards recommendations through a structured process of statement development. The Delphi method was chosen to gather expert opinions on complex issues and reach consensus [19]. This method for strategic decision-making to develop policy addresses critical gaps where direct evidence is limited or available [20]. While no universally accepted guidelines exist for conducting Delphi studies [21, 22], adherence to the CREDES (Conducting and REporting of DElphi Studies) guidelines ensures methodological rigor [22–24].

This study aimed at synthesizing positions for improving RSV surveillance, enhancing diagnostic approaches, prioritizing high-risk adult populations for vaccination, and evaluating healthcare utilization, alongside vaccine cost-effectiveness, to lead to expert recommendations.

Methods

Study Design

Twelve experts from six Asian countries, Singapore, Indonesia, Malaysia, the Philippines, Thailand, and Taiwan, participated in the Delphi expert panel. All participants are specialists with demonstrated expertise in RSV disease management and with experience in clinical research, including authorship of relevant peer-reviewed publications or participation in national surveillance and guideline development. The study commenced with a virtual meeting between the experts to discuss and align the methodology, objectives, and collaborative expectations.

A modified Delphi technique was adopted for this study, as recently used by Zhang et al. in their expert consensus on diagnosis and management of RSV in children [25]. This modified Delphi consensus study commenced with a literature search using a structured but flexible approach to gather relevant evidence on global data, insights, and recommendations, particularly relevant to older adult populations in Asia. The approach utilized multiple keywords to search through electronic databases, including PubMed, Google Scholar, Scopus, and Google. The search covered all relevant publications from the earliest available records in each database through August 2024, focusing on terms such as “respiratory syncytial virus”, “RSV”, “lower respiratory tract infection”, “bronchiolitis”, “viral pneumonia”, “adults”, “elderly”, “Asia”, “surveillance”, “epidemiology”, “case definition”, “diagnosis”, “vaccines”, and “recommendations”. Additionally, the search was extended to reviewing references from selected articles to ensure comprehensive coverage. Unlike traditional literature search, which lacks a structured search strategy, and systematic search, which requires screening based on results from fixed consolidated search strings, this semi-systematic literature search approach used predefined keywords and thematic mapping to create a transparent evidence map [26]. This preparatory phase informed the development of the first round of an online questionnaire that posed anonymous, closed-ended questions (item 1, Supplementary Material). All phases of the study—from preparatory work and expert selection process to iterative survey rounds—were conducted by Transform Medical Communications in strict accordance with the CREDES guidelines [22]. The purpose and methods of the study were clearly outlined at the outset with defined procedures established for the first and subsequent Delphi rounds. To ensure that the modified Delphi consensus study recommendations remained current, the narrative literature review was continually updated (last updated April 2025) to capture any newly published evidence. Delphi voting and consensus recommendation developments were carried out exclusively by the independent expert panel members.

Results analyzed from the first round were shared with all Delphi panel members to show the overall distribution of all responses and to indicate which questions had reached consensus. Questions that reached the consensus threshold were removed from the subsequent round(s) of the online, closed-ended, anonymous survey. Strategies for subsequent round(s) included rephrasing questions, adding new questions, or combining similar topics into a single question based on feedback and insights gained from the first round.

Ethical Approval

Not applicable; the Delphi approach relied solely on expert opinions and previously published information without involving any patient data. Both surveys were anonymous and closed-ended.

Consensus Development Process and Code of Conduct

For the first round of the survey, a consensus was predefined as at least 75% of the participants selecting the same response in multiple-choice questions (MCQs) or showing agreement on Likert-scale questions (i.e., selecting “Agree” or “Strongly agree”, “Adequately” or “Very adequately”, “Important” or “Critically important”, “Important” or “Critically important”, or “Important” or “Most important”). Agreement of ≥ 90% was regarded as a strong consensus. The same technique was implemented for subsequent rounds of the survey; however, if the two most frequently selected response options in a MCQ were not mutually exclusive and their combined proportion of endorsements was ≥ 75%, those two options were merged into a single recommendation. For questions based on ranking, Krippendorff’s alpha (k-alpha) coefficient was calculated to quantify the agreement among the experts on the order of priority [27] using an online k-alpha calculator with masked, coded data. A bootstrap method with 1000 samples was applied to compute 95% confidence intervals for the alpha values to ensure the generalizability of the ranking findings. As discussed by Del Grande et al., k-alpha was interpreted as follows: k-alpha ≥ 0.80 for confirming ranking and ≥ 0.67 for informing tentative conclusions, while k-alpha < 0.67 indicated insufficient agreement [27].

Themes and Objectives of Survey Questionnaires

The survey questionnaires covered four key areas:

• Theme 1: Exploring the epidemiology and surveillance of RSV in older adults across Asia (“epidemiology and surveillance”).

  Objective: Understand the underascertainment magnitude of RSV disease in older adults and the utility of RSV surveillance in Asia.

• Theme 2: Strategies to accurately diagnose RSV among older adults in Asia (“diagnosis of RSV infection”).

  Objective: Explore the development and refinement of clinical case definitions and optimize diagnostic strategies for accurately determining the incidence and establishing the clinical outcomes of RSV disease among older adults in Asia.

• Theme 3: Defining the eligible high-risk adult populations and their strategic prioritization for vaccination in Asia (“high-risk adult populations”).

  Objective: Identify adult populations at high-risk of severe RSV infections in Asia to prioritize these groups in vaccination campaigns.

• Theme 4: Assessment of RSV-related healthcare utilization, economic impact, and cost-effectiveness of vaccines (“healthcare utilization”).

  Objective: Understand the importance of strategies for assessing healthcare utilization, economic load, and cost-effectiveness of RSV vaccines for older adults in Asia.

Results

In the first round of the Delphi process, the expert panelists answered 30 survey questions: two about their experience and expertise, and 28 on the four key themes. The panel included six (50%) pulmonologists, four (33%) infectious disease physicians, and two (17%) geriatricians. Nine (75%) experts had more than 20 years of experience managing respiratory infections, two (17%) had 10–20 years, and one (8%) had 5–10 years; none had fewer than 5 years of experience. The first round of an online, closed-ended, anonymous questionnaire was completed by all 12 expert panel members between 6 and 23 November 2024.

Consensus was reached on all theme 1 (“epidemiology and surveillance”) questions. However, 12 questions across themes 2 to 4 did not reach a consensus in the first round: five from theme 2 (“diagnosis”), four from theme 3 (“high-risk adult populations”), and three from theme 4 (“healthcare utilization”). Item 2 in the Supplementary Material summarizes the scientific questions from the first round, their corresponding results, and the strategic decisions made for the second round of the survey. Table 1 provides a summary of the first survey items, consensus levels, and supporting evidence for recommendations. For the second round, questions that reached the consensus threshold were removed from the online, closed-ended, anonymous survey (item 3, Supplementary Material). This second round, completed by all 12 expert panel members between January 20 and January 27, 2025, included 14 questions. Item 4 in the Supplementary Material summarizes the main questions from the second round, their results, and the rationale for concluding the study without further rounds. In the second round, consensus was reached on eight of the previously unresolved 12 questions. For “diagnosis of RSV infection” (theme 2), three of the five questions reached consensus. The remaining two questions—one on the most important parameter(s) for laboratory confirmation of RSV infection and the other on the ideal time frame for obtaining a sample for RSV testing in hospitalized patients—each had two complementary response options. Since the combined endorsement for the two complementary options exceeded 75%, they were merged into a single unified recommendation for each question. For “high-risk adult populations” (theme 3), three of four questions reached consensus, but the question on recommended populations in Asia that should be a priority for RSV vaccination was consolidated by merging the top two non-exclusive responses that met the 75% threshold. In “healthcare utilization” (theme 4), consensus was reached for two of three questions. The last question did not reach a consensus, with only half of the experts supporting the importance of distinguishing between RSV-A and RSV-B in clinical studies. No further survey round was conducted for this question. Table 2 provides a summary of the second survey items, consensus levels, and supporting evidence for recommendations.

Table 1.

Summary of round 1 Delphi survey items, consensus levels, and supporting evidence for recommendations

Item*	Level of consensus, recommendation statement (if consensus achieved), and strategy for next round (if no consensus achieved)**	Supporting literature for the recommendation
Theme 1: Epidemiology and surveillance
Adequacy of current surveillance systems in capturing RSV burden (frequency or incidence) in elderly	Consensus: 83% of panelists rated it “inadequate” or “very inadequate” Recommendation statement: Current surveillance systems should be enhanced in Asia to more accurately capture the burden (frequency or incidence) of RSV infection among elderly populations	Surveillance protocols for elderly patients exist in only a few countries in Asia (such as China, Japan, Singapore, and South Korea), and most other nations lack any structure for systematic data collection [2, 9–13]
Prioritization of research efforts to better understand the burden of RSV in older adults and impact of preventive interventions	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: Research efforts to better understand the burden (clinical and economic) of RSV in older adults in Asia and the potential impact of preventive interventions should be prioritized	In Asia, RSV infections in older adults remain substantially underreported even though they lead to a complicated clinical course, particularly among patients with comorbidities [2] Economic burden analyses for RSV disease in older adults are also limited in Asia [14] Strengthening local epidemiological studies and surveillance platforms in Asia will generate the critical baseline data for enhancing RSV disease awareness, and guide future vaccination strategies and resource allocation [12, 17, 18]
Make RSV a public health priority in older adults	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: Focus on RSV as a public health priority in older adults should be increased, given the high estimated burden (clinical course and mortality rates)
Need for well-designed local RSV surveillance studies	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: Well-designed local surveillance studies should be conducted that are crucial for quantifying RSV disease to assess vaccine effectiveness
Integration of RSV surveillance with influenza and COVID-19 systems	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: RSV surveillance should be integrated with existing influenza and COVID-19 monitoring systems, as this approach will be beneficial for public health and could be cost-effective	Integrating RSV surveillance with existing influenza monitoring systems is a useful strategy to streamline surveillance efforts with minimal additional cost and effort [15]
Theme 2: Diagnosis of RSV infection
Need for a standardized protocol for clinical case definitions, diagnostic techniques, and reporting	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: There is a significant need for a standardized protocol for clinical case definition(s), recommended diagnostic techniques, and uniform methods for reporting RSV epidemiology to ensure consistent and comprehensive burden estimations	Currently, RSV surveillance employs a variety of case definitions and diagnostics [28]. Accurate RSV diagnosis relies on consistent case definitions, sensitive assays [15, 30], and optimized sampling methods [15, 31, 32]
Outpatient case definition recommendation. List included (i) ARI, (ii) modified ARI that specifically includes cough as one of the symptoms, or (iii) neither of the two	No consensus. However, majority (50%) voted for “standard ARI definition”. Hence in 2nd round of survey, the question was converted to 5-point Likert to check the level of agreement among panelists for recommendation of use of “standard ARI” as case definition for outpatients. Additional clarity on ARI that it does not include the need for fever was also added	NA
Inpatient case definition recommendation. List included (i) SARI, (ii) extended SARI (without requirement of fever), or (iii) neither of the two	Strong consensus: 100% of panelists voted for extended SARI as the case definition Recommendation statement: An extended SARI case definition that removes the requirement of fever as one of the mandatory criteria is recommended for diagnosing RSV in older adults who are hospitalized	Diagnosing RSV in hospitalized older adults is challenging, as they present with fewer febrile signs, which results in underestimation when ILI or SARI definitions are applied [15, 28]. In WHO pilot for RSV surveillance, use of extended SARI increased detection of RSV infections [43]
Settings where RSV testing should occur. List included (i) hospitalized patients (ii) hospitalized and ED patients, (iii) hospitals, ED, and clinics, (iv) hospitals, ED, clinics, and community/aged care centers, or (v) hospitals, ED, clinics, community/aged care, and primary care/GP settings	No consensus. However, majority (50%) voted for “hospitals, emergency departments, clinics, community centers/aged care settings, and primary care/GP settings”. Hence in 2nd round of survey, the question was rephrased for clarity and made simpler with only 3 options: (i) hospitalized patients, (ii) both hospitalized patients and ED settings, (iii) all healthcare settings, including hospitals, EDs, and outpatient clinics	NA
Ranking of practical considerations to implement RSV tests. List included (i) accuracy (specificity), (ii) reliability (sensitivity), (iii) cost, (iv) ease of use, and (v) turnaround time for results	No consensus. k-alpha 0.167 (CI − 0.004 to 0.285). In 2nd round of survey, the question was modified into a simple MCQ asking what would be the most important parameter for laboratory confirmation of RSV and choices included (i) sensitivity, (ii) specificity, (iii) both sensitivity and specificity, with focus on sensitivity, (iv) both sensitivity and specificity, with focus on specificity, (v) neither of the above	NA
Most suitable diagnostic methods in clinical settings. List included (i) RT-PCR/ qPCR, (ii) viral culture, (iii) RAD tests, (iv) IFA assay/DFA assay, (v) multi-pathogen nucleic acid amplification test	No consensus. k-alpha 0.581 (CI 0.055–0.770). However, as RT-PCR/qPCR ranked top, in the 2nd round of survey, the question was modified into 5-point Likert to check the level of agreement among panelists for recommendation for RT-PCR/qPCR as the most suitable diagnostic tests for RSV in older adults	NA
Diagnostic strategy: RAD first then qRT-PCR for negatives	Consensus: 75% of panelists “strongly agree” or “agree” Recommendation statement: Using RAD tests initially for all suspected cases, followed by quantitative RT-PCR for RAD test-negative cases can be considered due to the varying availability and accessibility of RSV diagnostic tests	PCR-based tests, especially real-time methods, provide superior sensitivity and specificity, but RAD tests remain the standard in resource-limited settings [15]
Recommended specimen types. List included (i) NPS, (ii) saliva, (iii) sputum (if present), (iv) OPS, (v) combinations of above	Strong consensus: 91.7% of panelists voted for a combination of specimens for accurate diagnosis of RSV in older adults Recommendation statement: Some combination of NPS, saliva, OPS and sputum (if present) is recommended for accurately diagnosing RSV in older adults	OPS, saliva, sputum, and serological testing alongside NPS significantly improves RSV detection in adults [15, 31, 32]
Optimal sampling window for outpatients. List included (i) within 10 days after onset of symptoms, (ii) within 4 days after onset of symptoms	Strong consensus: 91.7% of panelists voted that within 4 days of onset was the ideal time for obtaining a sample for outpatients Recommendation statement: The ideal time frame for obtaining a sample for RSV testing to ensure the most accurate results in outpatients is within 4 days after onset of symptoms	ECDC recommends testing within 4 days of symptom onset or promptly after hospital admission, up to 10 days post onset [15]
Optimal sampling window for inpatients. List included (i) as soon as possible upon hospital admission, (ii) within 1 day, (iii) within 3 days of hospital admission	No consensus. However, the majority (66.7%) voted for “as soon as possible upon hospital admission” followed by “within 1 day” (16.7%). Hence in 2nd round of survey, the response options were modified as (i) within 24 h of hospital admission, (ii) within 48 h of hospital admission, (iii) within 72 h of hospital admission	NA
Theme 3: High-risk adult populations
Universal RSV vaccination for all adults 75 years and older	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: A universal RSV vaccination should be recommended for all adults 75 years and older (once RSV vaccines are licensed for use)	Adults aged ≥ 75 years face higher risk of severe RSV outcomes [34]. US ACIP recommends “universal RSV vaccination” for all adults aged 75 years and older [34]
Universal RSV vaccination for all adults 60 years and older	No consensus. 50% of panelists “strongly agree” or “agree”. Hence in 2nd round of survey, the question was modified to check the level of agreement among panelists for recommendation for RSV vaccination for adults 60 years and older with clinician determined risk factors for severe viral respiratory disease	NA
RSV vaccination for adults 60 years and older with chronic comorbid conditions	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: A universal RSV vaccination should be recommended for all adults 60 years and older with chronic comorbid conditions (once RSV vaccines are licensed for use)	US ACIP recommends RSV vaccination for adults ≥ 60 years with risk conditions [34] However, apart from integrating RSV vaccination into adult immunization programs, refining high-risk group criteria is key to improving prevention [35]
RSV vaccination for adults 60 years and older with immunocompromised states	Strong consensus: 100% of panelists “strongly agree” or “agree” Recommendation statement: A universal RSV vaccination should be recommended for all adults 60 years and older with immunocompromised state (once RSV vaccines are licensed for use)
RSV vaccination for adults 60 years and older residing in long-term care facilities	Strong consensus: 91.7% of panelists “strongly agree” or “agree” Recommendation statement: A universal RSV vaccination should be recommended for all adults 60 years and older residing in long-term care facilities (once RSV vaccines are licensed for use)
Ranking for priority groups for vaccination. List included (i) all adults aged ≥ 75, (ii) all adults aged ≥ 60, (iii) adults aged ≥ 60 with comorbidities, (iv) adults aged ≥ 60 years with IC conditions, (v) adults aged ≥ 60 years in long-term care facilities	Consensus not reached; k-alpha 0.555 (CI 0.043–0.647) In 2nd round of survey, this question was modified into a MCQ to select priority groups for vaccination. The response options included (i) all adults aged ≥ 75; (ii) adults aged ≥ 60 with risk factors, (iii) adults aged ≥ 50 with risk factors, (iv) both older and younger adult risk groups	NA
Coadministration of RSV and flu vaccines as a standard practice	Consensus: 75% of panelists “strongly agree” or “agree” Recommendation statement: Coadministration of RSV and influenza vaccines could be considered in clinical practice	According to US CDC recommendations, administering RSV vaccines alongside influenza and COVID-19 vaccines is acceptable [36]
Coadministration of RSV and COVID-19 vaccines as a standard practice	No consensus. 66.7% of panelists “strongly agree” or “agree”. In 2nd round of survey, this question was modified as: Do you agree that the coadministration of RSV and COVID-19 vaccines could be considered in clinical practice?	NA
Coadministration of RSV, flu, and COVID-19 vaccines as a standard practice	No consensus. 50% of panelists “strongly agree” or “agree”. In 2nd round of survey, this question was modified as: Do you agree that the coadministration of RSV, influenza, and COVID-19 vaccines could be considered in clinical practice?	NA
Theme 4: Healthcare utilization
Adjustment factor for underestimation of RSV hospitalizations in Asia	No consensus. However, most panelists recommended an adjustment factor “much higher than 2.2” (50%), followed by “2.2” (25%) for Asia. Hence, in the 2nd round of survey, this question was modified to a Likert scale to check the recommendation for “2.2-fold or higher” adjustment factor	NA
Temporal strategy for adult RSV surveillance in Asia (when to test and measure healthcare and economic burden based on seasonality and outbreak triggers)	No consensus. However, majority of panelists (58.3%) recommended that surveillance should be conducted each year. Hence, in the 2nd round of survey, this question was modified to a Likert scale to check the recommendation for year-round RSV surveillance	NA
Importance of distinguishing RSV-A vs RSV-B	No consensus. 33.3% of panelists rated it “critically important” or “important”. In 2nd round of survey, this question was made more specific by including its clinical importance specific for Asia	NA
Objectives for local cost-effectiveness analyses	Strong consensus: 91.7% of panelists chose “all of the above” for the primary objectives for conducting local cost-effectiveness analyses for RSV vaccines Recommendation statement: The objectives for conducting local cost-effectiveness analyses for RSV vaccines could include (i) estimation of the economic impact of vaccination in eligible population, (ii) providing evidence for authority decisions on healthcare budget allocations, (iii) improving community engagement and trust, and (iv) providing insights into potential direct and indirect benefits of vaccination	Local surveillance data inform decision-making and policy development for prevention, diagnostics, and healthcare delivery [12, 17]. Economic evaluations clarify public health and healthcare impact, especially in high-risk groups [7, 11]
Importance of strategies to address RSV burden	Consensus. ≥ 75% of panelists rated 6 of 8 listed tactics^ as “more important” or “most important” and these were used to formulate the strategies below for effectively addressing RSV burden in older adults:  Collecting comprehensive disease burden data to understand the scope of RSV impact (voted for by 83.3%)  Developing affordable and reliable diagnostic tools for rapid RSV detection (voted for by 83.3%)  Launching targeted public health campaigns to increase awareness of RSV risks and prevention among older adults (voted for by 75%)  Educating healthcare providers on the importance of early RSV diagnosis and appropriate management (voted for by 75%)  Strengthening collaborations with policymakers and healthcare payers to secure funding & support for RSV initiatives (voted for by 83.3%)  Ensuring timely access to new medical interventions such as vaccines (voted for by 83.3%)	Effective prevention and management of RSV in older adults in Asia revolves around supporting decision-making and formulating policies aimed at enhancing prevention, diagnostics, and healthcare service delivery [2, 7, 11–13]

ACIP Advisory Committee on Immunization Practices, ARI acute respiratory infection, CDC Centers for Disease Control and Prevention, CI confidence interval, DFA direct fluorescent antibody assay, ECDC European Centre for Disease Prevention and Control, ED emergency department, GP general practitioner, IC immunocompromising, IFA immunofluorescence assay, ILI influenza-like illness, k-alpha Krippendorff’s alpha, MCQ multiple-choice question, NA not applicable, NPS nasopharyngeal swab, OPS oropharyngeal swab, PCR polymerase chain reaction, RAD rapid antigen detection, RSV respiratory syncytial virus, RT-PCR reverse transcriptase polymerase chain reaction, SARI standard severe acute respiratory infection, qPCR real-time polymerase chain reaction, US United States

*For full question, please refer to supplementary items 1 and 2 in the Supplementary file

**Consensus was defined as at least 75% of the participants selecting the same response in MCQs or showing agreement on Likert scale questions; agreement by ≥ 90% was regarded as strong consensus. For ranking questions, k-alpha < 0.67 indicated insufficient agreement

^No consensus reached for “implementing robust RSV vaccine delivery programs in anticipation of new vaccine availability” (voted for by 58.3% of panelists) and “incorporating RSV education into routine healthcare visits, especially during flu season” (voted for by 66.7% of panelists) and these statements were not included in recommended strategies

Table 2.

Summary of round 2 Delphi survey items, consensus levels, and supporting evidence for recommendations

Item*	Level of consensus, recommendation statement (if consensus achieved), and strategy for next round (if no consensus achieved)**	Supporting literature for the recommendation
Theme 1: Consensus was reached on all questions during round 1 survey
Theme 2: Diagnosis of RSV infection
Use a standard ARI case definition (without the need for fever) for diagnosing RSV in outpatient older adults	Strong consensus: 91.7% of panelists voted for “recommendation” or “strong recommendation”	Outpatient use of an “ARI” criteria (acute onset of cough or other respiratory symptoms without fever) could increase diagnostic sensitivity and specificity in outpatients [15, 28]. In WHO pilot for community RSV surveillance, use of ARI increased detection of RSV infections [43]
	Recommendation statement: A standard ARI case definition (without the need for fever) for diagnosing RSV in outpatient settings for older adults
Setting for RSV testing to optimize completeness of burden data. List included (i) only in hospitalized patients, (ii) in both hospitalized patients and ED settings, (iii) in all healthcare settings, including hospitals, EDs, and outpatient clinics	Consensus: 75% of panelists agreed that RSV testing should be conducted in all healthcare settings	The routine diagnostics for RSV in adult patients, particularly in outpatient settings, are seldom conducted despite significant amount of disease burden in outpatients [7, 13, 17]
	Recommendation statement: RSV testing should be conducted in all healthcare settings, including hospitals, EDs, and outpatient clinics to optimize the completeness of RSV disease burden data
Most important parameter for laboratory confirmation in clinical settings. List included (i) specificity (true negative rate), (ii) both sensitivity and specificity, with focus on sensitivity, (iii) both sensitivity and specificity, with focus on specificity, (iv) neither of these	Two nonexclusive response options (“both sensitivity and specificity, with focus on sensitivity” and “both sensitivity and specificity, with focus on specificity”) voted for by 83.3% of panelists were merged into a single recommendation	Historically, viral culture was considered the gold standard due to its high specificity, but its limited sensitivity, labor-intensive nature, and lengthy duration of the assay deter its real-world use [25, 30]. PCR-based assays offer good sensitivity (86.4–100%) and specificity (97.7–100%), along with a rapid turnaround time [30]
	Recommendation statement: For laboratory confirmation of RSV infection, both sensitivity and specificity are equally important parameters in clinical settings
RT-PCR and qPCR are the most suitable diagnostic tests for RSV in older adults	Strong consensus: 100% of panelists “strongly agree” or “agree”	Since older adults with RSV shed lower viral titers than infants, PCR-based tests, especially real-time methods, offer more reliable detection in this population [15, 30]
	Recommendation statement: RT-PCR and qPCR are the most suitable diagnostic tests for RSV in older adults
Ideal time frame for obtaining a sample in hospitalized patients. List included (i) within 24 h of hospital admission, (ii) within 48 h of hospital admission, (iii) within 72 h of hospital admission	Two nonexclusive response options (“within 24 h of admission” and “within 48 h of admission”) voted for by 100% of panelists were merged into a single recommendation	The ECDC Advisory Forum recommends storing specimens at 4 °C if tested within 1–2 days or at − 70 °C or below if delayed [15]
	Recommendation statement: The ideal time frame for obtaining a sample for RSV testing to ensure optimal sensitivity and specificity in hospitalized patients is within 24–48 h of hospital admission
Theme 3: High-risk adult populations
RSV vaccination for adults 60 years and older with risk factors that a healthcare provider determines would increase the risk for severe disease due to viral respiratory infection	Strong consensus: 100% of panelists “strongly agree” or “agree”	Adults ≥ 75 years and those with chronic conditions face a higher risk of severe RSV outcomes [34]. US ACIP recommends RSV vaccination for all adults aged ≥ 75 years and those ≥ 60 years with risk conditions [34] However, apart from integrating RSV vaccination into adult immunization programs, refining high-risk group criteria is key to improving prevention [35]
	Recommendation statement: A universal RSV vaccination should be recommended for all adults 60 years and older with risk factors that a HCP determines would increase the risk for severe disease due to viral respiratory infection (once RSV vaccines are licensed for use)
Priority populations in Asia for RSV vaccination of older adults. List included (i) all adults aged ≥ 75, (ii) all adults aged ≥ 60 with risk factors, (iii) all adults aged ≥ 50 with risk factors, (iv) older age and younger adult age groups with medical risk factors	Two nonexclusive response options voted for by 83.3% of panelists were merged into a single recommendation
	Recommendation statement: All populations 75 years and above and those ≥ 60 years with risk conditions should be a priority for RSV vaccination in Asia (once RSV vaccines are licensed for use)
Consideration of coadministration of RSV and COVID-19 vaccines	Strong consensus: 91.7% of panelists “strongly agree” or “agree”	According to CDC recommendations, administering RSV vaccines alongside influenza and COVID-19 is acceptable [36]
	Recommendation statement: Coadministration of RSV and COVID-19 vaccines could be considered in clinical practice
Consideration of coadministration of RSV, influenza, and COVID-19 vaccines	Consensus: 83.3% of panelists “strongly agree” or “agree”
	Recommendation statement: Coadministration of RSV, influenza, and COVID-19 vaccines could be considered in clinical practice
Theme 4: Healthcare utilization
Use an adjustment factor of ≥ 2.2 to correct underestimation of RSV-associated hospitalizations in older adults in Asia	Consensus: 83.3% of panelists “strongly agree” or “agree”	The unadjusted RSV hospitalization rate was 157 per 100,000 in adults ≥ 65 years. After adjustment for underascertainment due to single-swab testing, this rate increased 2.2 × to 347 per 100,000 [3]. Additional multipliers, however, apply for undertesting/non-PCR testing/narrow case definitions
	Recommendation statement: An adjustment factor of 2.2-fold or higher! would be required to adjust for underestimation of RSV-associated hospitalizations in older adults in Asia
Introduction of year-round RSV surveillance in Asia	Strong consensus: 100% of panelists “strongly agree” or “agree”	The RSV seasonality in subtropical areas varies, with peaks occurring at different times and some countries may experience secondary peaks or even year-round RSV activity [37]. For an effective year-round surveillance, especially in the initial years, RSV monitoring should be continuous [15]
	Recommendation statement: The introduction of year-round surveillance for RSV based on testing and measurement of the related healthcare and economic burden is required
Importance of distinguishing RSV-A and RSV-B for epidemiology and vaccine effectiveness studies (keeping in mind substantial global RSV burden by both subgroups including in Asia)	Consensus was not reached; 50% of panelists rated that RSV subtyping is “critically important” or “important”. No further survey was conducted for this question as assays differentiating RSV subgroups is expensive and not as widely accessible in Asia	NA

ACIP Advisory Committee on Immunization Practices, ARI acute respiratory infection, CDC Centers for Disease Control and Prevention, ECDC European Centre for Disease Prevention and Control, ED emergency department, HCP healthcare provider, HIC high-income countries, MCQs multiple-choice questions, NA not applicable, PCR polymerase chain reaction, RSV respiratory syncytial virus, RT-PCR reverse transcriptase polymerase chain reaction, qPCR real-time polymerase chain reaction, WHO World Health Organization, US United States

*For full question, please refer to supplementary items 3 and 4 in the Supplementary file

**Consensus was defined as ≥ 75% of the participants selecting the same response in MCQs or showing agreement on Likert scale questions; agreement by ≥ 90% was regarded as strong consensus. If the two most frequently selected response options in MCQs were not mutually exclusive and their combined proportion of endorsements was ≥ 75%, those two options were merged into a single recommendation

^!Specifically for underestimation due to single-swab PCR testing, does not cover underascertainment for narrower case definitions, etc.

The overall consolidated recommendations for each theme are summarized in Table 3.

Table 3.

Summary of expert consensus and recommendations on surveillance, diagnosis, and prevention of RSV infection in older adults in Asia

Theme 1: Epidemiology and surveillance of RSV in older adults across Asia

1. surveillance systems should be enhanced in Asia to more accurately capture the burden (frequency or incidence) of RSV infection among elderly populations*

2. Research efforts to better understand the burden (clinical and economic) of RSV in older adults in Asia and the potential impact of preventive interventions should be prioritized*

3. Focus on RSV as a public health priority in older adults should be increased, given the high estimated burden (clinical course and mortality rates)*

4. Well-designed local surveillance studies should be conducted that are crucial for quantifying RSV disease to assess vaccine effectiveness*

5. RSV surveillance should be integrated with existing influenza and COVID-19 monitoring systems, as this approach will be beneficial for public health and could be cost-effective*

Theme 2: Strategies to accurately diagnose RSV among older adults in Asia

6. There is a significant need for a standardized protocol for clinical case definition(s), recommended diagnostic techniques, and uniform methods for reporting RSV epidemiology to ensure consistent and comprehensive burden estimations*

7. A standard ARI case definition^ (without the need for fever) for diagnosing RSV in outpatient settings for older adults**

8. An extended SARI case definition# that removes the requirement of fever as one of the mandatory criteria is recommended for diagnosing RSV in older adults who are hospitalized*

9. RSV testing should be conducted in all healthcare settings, including hospitals, EDs, and outpatient clinics to optimize the completeness of RSV disease burden data**

10. For laboratory confirmation of RSV infection, both sensitivity and specificity are equally important parameters in clinical settings***

11. RT-PCR and qPCR are the most suitable diagnostic tests for RSV in older adults**

12. RAD tests initially for all suspected cases, followed by quantitative RT-PCR for RAD test-negative cases can be considered due to the varying availability and accessibility of RSV diagnostic tests*

13. Some combination of NPS, saliva, OPS, and sputum (if present) is recommended for accurately diagnosing RSV in older adults*

14. The ideal time frame for obtaining a sample for RSV testing to ensure the most accurate results in outpatients is within 4 days after onset of symptoms*

15. The ideal time frame for obtaining a sample for RSV testing to ensure optimal sensitivity and specificity in hospitalized patients is within 24–48 h of hospital admission***

Theme 3: Defining the eligible high-risk adult populations and their strategic prioritization for vaccination in Asia

16. A universal RSV vaccination should be recommended for all adults 75 years and older (once RSV vaccines are licensed for use)*

17. A universal RSV vaccination should be recommended for all adults 60 years and older with chronic comorbid conditions (once RSV vaccines are licensed for use)*

18. A universal RSV vaccination should be recommended for all adults 60 years and older with immunocompromised state (once RSV vaccines are licensed for use)*

19. A universal RSV vaccination should be recommended for all adults 60 years and older residing in long-term care facilities (once RSV vaccines are licensed for use)*

20. A universal RSV vaccination should be recommended for all adults 60 years and older with risk factors that a HCP determines would increase the risk for severe disease due to viral respiratory infection (once RSV vaccines are licensed for use)**

21. All populations 75 years and above and those ≥ 60 years with risk conditions should be a priority for RSV vaccination in Asia (once RSV vaccines are licensed for use)***

22. Coadministration of RSV and influenza vaccines could be considered in clinical practice*

23. Coadministration of RSV and COVID-19 vaccines could be considered in clinical practice**

24. Coadministration of RSV, influenza, and COVID-19 vaccines could be considered in clinical practice**

Theme 4: Assessment of RSV-related healthcare utilization, economic impact, and cost-effectiveness of vaccines

25. An adjustment factor of 2.2-fold or higher! would be required to adjust for underestimation of RSV-associated hospitalizations in older adults in Asia**

26. The introduction of year-round surveillance for RSV based on testing and measurement of the related healthcare and economic burden is required**

27. The objectives for conducting local cost-effectiveness analyses for RSV vaccines could include (i) estimation of the economic impact of vaccination in eligible population, (ii) providing evidence for authority decisions on healthcare budget allocations, (iii) improving community engagement and trust, and (iv) providing insights into potential direct and indirect benefits of vaccination*

28. The following strategies are critical for effectively addressing RSV burden in older adults:  Collecting comprehensive disease burden data to understand the scope of RSV impact*  Developing affordable and reliable diagnostic tools for rapid RSV detection*  Launching targeted public health campaigns to increase awareness of RSV risks and prevention among older adults*   Educating healthcare providers on the importance of early RSV diagnosis and appropriate management*  Strengthening collaborations with policymakers and healthcare payers to secure funding & support for RSV initiatives*  Ensuring timely access to new medical interventions such as vaccines*

ARI acute respiratory infection, ED emergency department, HCP healthcare provider, MCQs multiple-choice questions, NPS nasopharyngeal swab, OPS oropharyngeal swab, RAD rapid antigen detection, RSV respiratory syncytial virus, RT-PCR reverse transcriptase polymerase chain reaction, SARI standard severe acute respiratory infection, qPCR real-time polymerase chain reaction

*Consensus formulated per results from round 1 survey (item 2, Supplementary file)

**Consensus formulated per results from round 2 survey (item 4, Supplementary file)

***Recommendations formulated per results from the round 2 survey where the two most frequently selected response options in MCQs were not mutually exclusive (item 4, Supplementary file)

^ARI case definition: Acute onset of symptoms with at least one respiratory sign/symptom such as cough and shortness of breath, sore throat, or coryza [43]

^#SARI definition: fever ≥ 38 °C, onset or re-exacerbation of cough or other respiratory symptoms within 10 days and requiring hospitalization (extended SARI case definition does not include fever as one of the criteria) [15, 28, 43]

^!Specifically for underestimation due to single-swab PCR testing and does not account for other reasons of underascertainment such as limited testing, use of non-PCR diagnostics, or narrower case definitions [3, 29, 32, 39]

Discussion

The findings from this modified Delphi consensus study reflect recommendations for four critical areas (themes) in addressing RSV among older adults in Asia: epidemiology and surveillance, diagnostic strategies, prioritization of high-risk populations for vaccination, and assessment of healthcare utilization and vaccine effectiveness (Tables 1, 2, 3). Key recommendations are illustrated in Figs. 1, 2, 3, 4, and detailed rationales for each theme are presented below.

Fig. 1.

Key recommendations for RSV epidemiology and surveillance in older adults across Asia. This figure highlights the major consensus points from theme 1, focusing on the need to improve surveillance, integrate RSV monitoring into established respiratory disease networks, conduct rigorous local research, and prioritize RSV as a key public health concern for older adults in Asia. RSV respiratory syncytial virus

Fig. 2.

Key recommendations for accurate RSV diagnosis in older adults across Asia. This figure highlights essential diagnostic strategies for identifying RSV in older adults. It illustrates how adopting case definitions that remove the requirement of fever, prioritizing PCR-based testing, using multiple specimen types, and carefully timing sample collection can improve detection rates and more accurately capture RSV’s true burden in Asia. ARI acute respiratory infection, NPS nasopharyngeal swab, OPS oropharyngeal swab, RAD rapid antigen detection, RSV respiratory syncytial virus, RT-PCR reverse transcriptase polymerase chain reaction, SARI standard severe acute respiratory infection, qPCR real-time polymerase chain reaction

Fig. 3.

Prioritizing high-risk adults for RSV vaccination in Asia. *Includes those with chronic conditions, immunocompromising states, residing in long-term care facilities, or risk factors that a clinician determines would increase the risk for severe disease due to viral respiratory infection. This figure outlines the expert consensus on RSV vaccination priorities in Asia (provided RSV vaccines are licensed for use), advocating a universal approach for older age groups and high-risk adults while also exploring potential benefits of coadministering RSV, influenza, and COVID-19 vaccines. RSV respiratory syncytial virus

Fig. 4.

Recommendations for assessment of RSV healthcare utilization, economic impact, and vaccine cost-effectiveness in Asia. *2.2 adjustment factor accounts for underestimation due to use of single nasal/NPS during PCR testing (instead of multiple specimens). Additional multipliers may apply for undertesting, non-PCR testing (e.g., RAD), and narrow case definitions. This figure summarizes key recommendations for addressing RSV’s clinical and economic impact in Asia. It highlights the need for adjusting hospitalization estimates, year-round surveillance, tailored cost-effectiveness studies, and strategic actions, ranging from improved diagnostics to stakeholder collaboration, to mitigate RSV burden in older adults. ARI acute respiratory infection, NPS nasopharyngeal swab, PCR polymerase chain reaction, RAD rapid antigen detection, RSV respiratory syncytial virus

Theme 1: Exploring Epidemiology and Surveillance of RSV in Older Adults Across Asia

The overall consensus in this theme highlights the urgent need for comprehensive RSV epidemiological data among older adults in Asia. The existing literature also points to significant gaps in RSV surveillance in most nations in Asia [2, 10, 13]. In contrast, Europe and North America have comprehensive RSV surveillance and older adult epidemiology [2, 10, 12, 17, 18]. Strengthening local epidemiological studies and surveillance platforms in Asia will generate the critical baseline data for enhancing RSV disease awareness, and guide future vaccination strategies and resource allocation [12, 17, 18]. The recommendation from this consensus for integrating RSV surveillance into existing influenza and COVID-19 monitoring platforms (Fig. 1) would streamline surveillance efforts while still using existing resources [15]. Achieving these goals will require collaboration among healthcare providers, policymakers, and industry partners.

Theme 2: Strategies to Accurately Diagnose RSV Among Older Adults in Asia

Diagnosing RSV infections in older adults can be challenging, since fewer present with febrile signs as compared to other age groups, leading to underestimation of RSV cases in older adults when only using conventional definitions for influenza-like illness (ILI) or standard severe acute respiratory infection (SARI) [28]. A pivotal study of 1040 community-dwelling Europeans aged 60 and above found that using ILI resulted in an up to nine-fold underestimation of RSV infection cases [29]. Hence, the panel in this study recommended modifying the SARI definition in hospitalized patients by removing fever as a mandatory criterion. Likewise, using “acute respiratory infection” criteria (acute onset of cough or other respiratory symptoms without the requirement of fever) in outpatient settings would enhance diagnostic sensitivity and specificity [15, 28]. Additionally, although polymerase chain reaction (PCR)-based tests, particularly real-time methods, offer superior accuracy (i.e., sensitivity and specificity), rapid antigen detection tests (RADTs) continue to be the standard of care in resource-limited environments [15]. As older adult patients with RSV infection shed lower virus titers when compared to neonates and young infants, PCR-based assays would more reliably detect RSV infection in older adults [30]. Sampling techniques are also important—nasopharyngeal swabs (NPS) remain optimal because they are more sensitive than oropharyngeal swabs (OPS) [15]. Adding other specimens, such as sputum and saliva, can further increase the likelihood of positive RSV detection [31]. Compared to NPS alone, expanding diagnostic methods such as OPS—to include saliva and sputum samples—and adding serological testing has improved sensitivity thereby significantly enhancing diagnosis rates by several-fold in adults [31, 32].

In this Delphi panel, the consensus recommendation was for RSV testing within 4 days of symptom onset in outpatients and within 24–48 h of hospital admission (Fig. 2). The ECDC (European Centre for Disease Prevention and Control) Advisory Forum recommends storing specimens at 4 °C if tested within 1–2 days or at − 70 °C or below if delayed. Although RSV shedding in adults in outpatient settings averages 9.8 ± 4.8 days, it can persist in immunocompromised patients [15]. As per the ECDC Advisory Forum, testing can be conducted within 10 days of symptom onset, but should ideally occur within 4 days and as soon as possible after hospital admission.

Theme 3: Defining the Eligible High-Risk Adult Populations and Their Strategic Prioritization for Vaccination in Asia

Individuals 75 years of age and above and adults with chronic conditions are at heightened risk of severe outcomes from RSV infection. Such conditions include chronic obstructive pulmonary disease, asthma, congestive heart failure, neuromuscular or neurological disorders, hepatic or renal impairment, or diabetes mellitus, as well as other risk conditions such as being a resident of a long-term care facility, manifesting frailty, or being immunocompromised (including organ transplant recipients) [1, 12, 33]. Under this theme, experts reached a consensus on recommending universal RSV vaccination (subject to national approval of RSV vaccines) for adults aged ≥ 75 years and for those ≥ 60 years with risk conditions (Fig. 3). This is consistent with the 2024 US Advisory Committee on Immunization Practices (ACIP) recommendations for RSV vaccination in adults [34]. Moving forward, integrating RSV vaccination into established adult immunization frameworks and continuing to refine criteria for high-risk groups will be crucial for enhancing RSV prevention efforts, especially with an additional approved indication for vaccination to prevent lower respiratory tract disease due to RSV in high-risk younger adult populations aged 18–59 years [35]. Currently, a single dose of the RSV vaccine is recommended. The randomized controlled clinical trials for vaccine efficacy demonstrate protection for at least two RSV seasons. Further studies are planned to determine the duration of this protection and to evaluate when subsequent revaccination would be necessary [36]. The consensus from this theme was that the coadministration of RSV vaccine with influenza, COVID-19, or both vaccines could be considered in clinical practice. According to the US Centers for Disease Control and Prevention (CDC) best practice recommendations for a temperate climate (Northern or Southern Hemisphere), administering RSV vaccines alongside other vaccines like those for influenza and COVID-19 is acceptable [36]. However, coadministration could lead to a greater frequency of local or systemic reactogenicity [36].

Although it is important to consider any seasonal patterns in planning vaccination campaigns, seasonality in subtropical region countries varies, with characteristic secondary peaks occurring throughout the year or with even year-round RSV activity observed [37]. Unlike the winter season predominance in temperate climates, RSV infections in tropical areas of Asia can peak during the wet seasons or during the Asia cold seasons in higher altitude settings [4]. The COVID-19 pandemic modified the typical RSV seasonality, which might not have fully returned to the pre-pandemic pattern yet [37]. Consequently, the recommendation from the US CDC, as noted by the American Medical Association in January 2025, was that RSV vaccination should be administered to eligible patients as soon as it is available [36].

Theme 4: Assessment of RSV-Related Healthcare Utilization, Economic Impact, and Cost-Effectiveness of Vaccines

Accurate measurement of RSV disease incidence and clinical outcomes requires a precise case definition, although this can be challenging because existing literature depends upon a range of clinical case definitions applied across studies [38]. Also, most of the available studies do not differentiate adequately between annual and seasonal rates, leading to underestimations by overlooking incidence during the peak respiratory virus season [7, 13, 17].

A recent systematic review analyzed 12 studies on RSV hospitalization rates among adults aged 65 years and older. The unadjusted hospitalization rate was 157 per 100,000 (95% CI 98–252). After adjustment for diagnostic testing-related underascertainment, this rate increased to 347 per 100,000 (203–595). When applied to high-income countries in 2019, the adjusted rate translates to approximately 787,000 (460,000–1,347,000) RSV-associated hospitalizations, roughly 2.2 times higher than the unadjusted estimate [3]. Hence, the consensus recommendation was that epidemiologists and researchers in Asia should consider an adjustment factor of ≥ 2.2 to address the underestimation of RSV-related hospitalizations [7, 13, 17] when utilizing data based on single-swab PCR testing with acute respiratory infection (ARI) case definition. This adjustment factor would not be able to address underascertainment due to undertesting [39], non-PCR testing (e.g., antigen or direct fluorescent antibody) [32], and narrow case definitions (e.g., ILI) [29]. Beyond hospitalized RSV infections, outpatient disease can represent a substantial burden to older adults, even if it does not always result in hospitalization. Diagnosis is rarely considered, in part because there is no specific licensed antiviral treatment for RSV in adults [7, 12].

Additionally, for a more representative determination of RSV disease epidemiology, there should be effective year-round surveillance in Asia (Fig. 4). Previous literature suggests that if this is not feasible, surveillance should at least focus on the peak season (for countries with a well-characterized RSV season) based on previous data trends. In this case, weekly reporting during the respiratory season and monthly updates thereafter are recommended to be maintained [15].

Local surveillance data is instrumental in supporting decision-making and formulating policies aimed at enhancing prevention, diagnostics, and healthcare service delivery for affected populations [12, 17]. The resulting evidence can help understand RSV disease impact on public health and healthcare systems, both in general and among high-risk populations, to guide estimation of the economic impact of vaccination in the eligible population vaccination strategies [7, 11]. Our study panel recommends that the objectives for conducting local cost-effectiveness analyses of RSV vaccines should also inform national authority decisions on healthcare budget allocations. Other key strategies suggested by our Delphi panel for effectively addressing the RSV burden among adults in Asia include gathering comprehensive disease data, developing affordable diagnostic tools, launching targeted public health campaigns, educating healthcare providers about early RSV diagnosis, collaborating with policymakers for adequate funding, and ensuring timely access to new medical interventions.

To our knowledge, no published Delphi studies focus exclusively on RSV in older adults. Existing Delphi efforts are pediatric in scope [25], while mixed-age ARI panels indirectly address RSV diagnosis within broader frameworks without older-adult specificity [40], and expert consensus statements for RSV prevention are not specific for older adults and Asia [41]. The present consensus addresses these gaps for Asia by reporting item-level agreements on RSV surveillance, diagnostics, and implementation of preventive strategies.

One limitation of this study is the lack of consensus on the value of distinguishing between RSV-A and RSV-B subgroups when assessing RSV clinical epidemiology (item 4, Supplementary Material). Both RSV-A and RSV-B contribute to the clinical burden, with their prevalence varying seasonally and often occurring simultaneously [42]. They are primarily distinguished by amino acid sequence differences in the G protein. Despite more than 90% similarity in the amino acid sequences of the F proteins, variations can be found in key antigenic regions of the pre-F configuration, such as Ø, IV, and V [42]. Current evidence suggests no major difference in clinical severity between RSV subgroups, though further research is required for older adult populations [5–8]. Some nucleic acid amplification tests can distinguish between RSV-A and RSV-B; however, despite their precision, these assays are not as widely accessible [25, 30]. Further research is required to determine how RSV-A and RSV-B subtyping can guide real-world vaccination strategies.

Additionally, while we invited pertinent clinician experts across Asia, their participation depended on interest and availability. Twelve experts from six diverse Asian nations agreed to collaborate for this study, and these countries captured geographic and health system diversity within Asia. However, the absence of experts from other countries in Asia limits the full representativeness of this study. Nevertheless, the representative countries in our study include both high-income nations and LMICs from Asia, along with those that follow mixed public–private financing with partial healthcare reimbursement models and have limited routine RSV testing and surveillance.

Conclusions

This Delphi panel provides a comprehensive set of expert recommendations for addressing the burden of RSV disease in older adults across Asia. Experts emphasized the need for integrating RSV monitoring with existing influenza and COVID-19 systems, applying standardized RSV disease case definitions, and expanding testing methods to improve case detection. A universal RSV vaccination strategy for adults aged ≥ 75 years and those ≥ 60 with risk conditions is recommended, alongside the consideration of coadministration with other vaccines like influenza and COVID-19, subject to locally approved vaccine labels. Furthermore, the Delphi panel advocates year-round RSV surveillance to inform policy decisions and to generate local cost-effectiveness analyses to optimize resource allocation. This expert consensus provides an RSV strategic plan to encourage enhanced diagnosis, surveillance, vaccination uptake, and vaccine resource allocation on behalf of older adult populations in Asia.

Supplementary Information

Below is the link to the electronic supplementary material.

Author Contributions

Yu-Jiun Chan, Philip Eng, Pin-Kuei Fu, Kuntjoro Harimurti, Kejal Hasmukharay, Sasisopin Kiertiburanakul, Asok Kurup, Yong Kek Pang, Edsel Maurice Salvana, Joel M. Santiaguel, Gurmeet Singh, Phunsup Wongsurakiat, Bulent Nuri Taysi, Mark A. Fletcher and Karan Thakkar made substantial contributions to the conception and design of the study, acquisition, analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work.

Funding

This study, development of the manuscript and the rapid service publishing fee was supported by Pfizer. Project management, data analytics and medical writing support were provided by Transform Medical Communications, which was funded by Pfizer. Medical writing support was provided by Dr. Sajita Setia, Director, Transform Medical Communications and was funded by Pfizer. Editorial support was provided by Dansoa Tabi-Amponsah, Medical Writer, Transform Medical Communications and was funded by Pfizer.

Data Availability

All supplementary tables generated during this study are included in this published article in the Supplementary Material. Other datasets generated during and/ or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Conflicts of Interest

Sasisopin Kiertiburanakul has received honoraria for lectures, served on advisory boards, and received congress travel grants from Pfizer. Yu-Jiun Chan, Philip Eng, Pin-Kuei Fu, Kuntjoro Harimurti, Kejal Hasmukharay, Sasisopin Kiertiburanakul, Asok Kurup, Yong Kek Pang, Edsel Maurice Salvana, Joel M. Santiaguel, Gurmeet Singh, and Phunsup Wongsurakiat were paid consultants to Pfizer in connection with the development of this manuscript. Bulent Nuri Taysi (BNT), Karan Thakkar (KT) and Mark A. Fletcher (MAF) are employees of Pfizer, a manufacturer of a subunit RSV vaccine indicated for older adults. Representatives of Pfizer (BNT, KT, and MAF) contributed to study design, selection of questionnaire items, and manuscript drafting, but they had no role in Delphi panel voting or consensus decision-making. The study authors, unaffiliated with Pfizer, exclusively generated the recommendations as sole members of the modified Delphi expert consensus panel.

Ethical Approval

Not applicable; the Delphi approach relied solely on expert opinions and previously published information without involving any patient data. Both surveys were anonymous and closed ended.