RSV vaccines

Respiratory syncytial virus (RSV) is a leading cause of severe lower‑respiratory‑tract illness in both high‑risk infants and older adults, prompting rapid development of a diverse portfolio of vaccines that includes protein‑subunit, mRNA, live‑attenuated, and vector‑based platforms. Central to modern RSV vaccine design is the stabilization of the prefusion F protein, which presents conserved neutralizing epitopes targeted by both active immunization and passive strategies such as long‑acting antibodies (e.g., nirsevimab). Clinical trials have demonstrated that a single dose can elicit robust humoral immunity in adults aged ≥60 years, while vaccination during pregnancy aims to transfer protective antibodies to newborns. Safety profiles are generally comparable to other routine respiratory vaccines, with mild to moderate reactogenicity and rare serious adverse events, although historical concerns about vaccine‑enhanced disease have shaped stringent regulatory pathways and post‑marketing surveillance. The burden of RSV differs markedly: pre‑term and other high‑risk infants experience high rates of hospitalization and mortality, whereas immunosenescent older adults face substantial morbidity and health‑care utilization. These epidemiologic realities drive prioritization strategies that balance economic considerations with equitable access, integrating RSV vaccines into existing national immunization schedules while addressing cold‑chain logistics and public‑health messaging. Ongoing molecular epidemiology informs strain selection and potential vaccine updates to maintain cross‑protective efficacy against evolving RSV genotypes worldwide.

Epidemiology and disease burden across age groups

The global burden of respiratory syncytial virus (RSV) is concentrated in two vulnerable populations: high‑risk infants and older adults.

High‑risk infants

Pre‑term infants—especially those born before 32 weeks gestation—experience the highest rates of RSV‑related hospitalization, intensive‑care unit admission, and mortality pre‑term birth. In low‑ and middle‑income countries, ≈ 97 % of RSV‑associated deaths occur in this age group, reflecting under‑developed lungs and immature immune defenses WHO. Because the first months of life constitute the period of greatest susceptibility, preventive strategies focus on long‑acting monoclonal antibodies (e.g., nirsevimab) and maternal immunization (e.g., Pfizer’s Abrysvo) to provide passive protection before the infant’s own immune system can mount an effective response monoclonal antibodies, maternal vaccination.

Older adults

In adults aged ≥ 60 years, RSV generates a disease burden comparable to influenza. Estimates for high‑income countries alone indicate ≈ 5.2 million cases, ≈ 470 000 hospitalizations, and ≈ 33 000 in‑hospital deaths each year, with an incidence of about 600.7 cases per 100 000 person‑years and a hospitalization rate of 157 per 100 000 epidemiology. Immunosenescence—characterized by reduced T‑cell function and chronic low‑grade inflammation (“inflammaging”)—diminishes the ability to clear infection, leading to severe lower‑respiratory‑tract disease, especially in individuals with chronic cardiopulmonary conditions immunosenescence, COPD, heart failure.

Implications for vaccine prioritization

The divergent burden patterns drive age‑specific prioritization strategies:

Older adults: Real‑world effectiveness studies report 58 %–92 % reductions in hospitalization and severe outcomes after a single dose of prefusion‑F protein vaccines, supporting universal recommendation for adults ≥ 75 years and for those 60–74 years with chronic risk factors or residing in long‑term care facilities vaccine effectiveness, adjuvanted vaccines. Seasonal timing (late summer/early fall) aligns vaccination with the onset of RSV circulation, maximizing protection before the peak season.
Infants: Because active immunization of neonates is limited by maternal antibody interference, passive approaches dominate. Nirsevimab is recommended for all infants < 8 months entering their first RSV season and for children 8–19 months with remaining risk factors, while maternal vaccination aims to transfer protective antibodies across the placenta during weeks 32–36 of gestation immunoprophylaxis, pregnancy.

These strategies reflect the need to match intervention type to the age‑specific immune context: long‑lasting active immunity for older adults versus immediate passive protection for newborns.

Summary of burden differences

Population	Primary clinical impact	Typical preventive approach	Key epidemiologic metric
High‑risk infants (pre‑term, < 8 months)	High hospitalization and mortality; long‑term respiratory sequelae	Long‑acting monoclonal antibody (nirsevimab) + maternal vaccination	≈ 97 % of global RSV deaths
Older adults (≥ 60 years)	Hospitalizations ~ 470 000 / yr; in‑hospital deaths ~ 33 000 / yr	Single‑dose prefusion‑F protein vaccine (mRNA or protein subunit)	Incidence ≈ 600.7 cases per 100 000 person‑years

Understanding these epidemiologic patterns is essential for public‑health planning, ensuring that resources are allocated to the groups bearing the greatest morbidity and mortality while tailoring vaccine or antibody regimens to the immunological realities of each age cohort.

Vaccine platforms and antigenic targets

RSV vaccine development has pursued several distinct platforms—each exploiting specific antigenic targets to elicit protective immunity while avoiding the historic risk of vaccine‑enhanced disease. The two surface glycoproteins most frequently selected are the prefusion F protein and the G protein, which together mediate viral entry and attachment to host cell receptors.

Prefusion‑stabilized F protein as the primary antigenic focus

Across protein‑subunit, mRNA, viral‑vector, and live‑attenuated candidates, the dominant design strategy is to present the prefusion conformation of the F protein. Stabilization of this conformation preserves a set of highly conserved neutralizing epitopes that are largely absent in the post‑fusion form, enabling the generation of high‑affinity antibodies that block viral membrane fusion prefusion F protein‑based vaccines^[1]. Bivalent formulations that incorporate prefusion F immunogens from both RSV‑A and RSV‑B strains have demonstrated broad cross‑strain neutralization, including activity against monoclonal‑antibody‑resistant variants bivalent prefusion F vaccines^[1].

G protein‑targeted designs

The G protein contributes to viral attachment via CX3CR1 binding and exhibits considerable antigenic variability. Inclusion of conserved regions from the G protein in some candidates—particularly those aimed at infants—expands the breadth of the immune response beyond the F protein alone, improving coverage against drifted strains G protein^[3].

Platform‑specific considerations

Platform	Antigen presentation	Immunogenicity profile	Typical target population
mRNA vaccine	Host cells translate mRNA encoding prefusion‑stabilized F (and optionally G) → intracellular expression of native‑like antigen	Strong neutralizing antibody titers; rapid antigen production; amenable to rapid redesign	Adults ≥ 60 yr (mRNA formulations)
Protein subunit vaccine	Purified prefusion F protein (often adjuvanted) delivered directly	Focused humoral response with established safety; no replication risk	Older adults; pregnant individuals for [[Maternal immunization
Live‑attenuated vaccine	Replication‑competent but weakened RSV expressing native F and G in their native conformations	Induces both humoral and cellular immunity (including mucosal IgA and T‑cell responses); broader antigenic exposure	Infants and toddlers (intranasal delivery)
Viral‑vector vaccine	Non‑replicating vector (e.g., adenovirus) delivers genes encoding prefusion F (sometimes G) → endogenous antigen expression	Combines robust antibody production with T‑cell activation; vector immunity may modulate efficacy	Adults and high‑risk adolescents

Live‑attenuated candidates leverage the native presentation of both F and G glycoproteins, potentially offering broader cross‑strain protection because the virus replicates and displays a full complement of surface antigens. However, achieving an optimal balance between attenuation and immunogenicity remains a key challenge, especially in the very young where safety margins are narrow.

Protein‑subunit and mRNA platforms benefit from structural optimization: prefusion F is engineered with stabilizing mutations (e.g., “DS‑Cav1” or “S2P” designs) that lock the protein in the antigenically favorable state. This precision reduces off‑target immune responses that could otherwise contribute to disease enhancement, a concern rooted in earlier formalin‑inactivated RSV vaccines.

Viral vectors, by delivering the F gene directly into host cells, exploit the endogenous antigen‑processing pathway, thereby stimulating both antibody‑mediated and cellular immunity. Nevertheless, pre‑existing anti‑vector immunity (particularly for common adenoviral serotypes) can attenuate vaccine efficacy, prompting the selection of rare serotypes or non‑human vectors.

Cross‑strain protection and durability

The structural stability of prefusion F correlates with the durability of neutralizing antibody titres; clinical data show efficacy persisting for at least two years in older adults, with bivalent formulations maintaining activity against emerging genotypes bivalent prefusion F vaccines^[1]. In contrast, live‑attenuated vaccines rely on ongoing viral replication to sustain immunity, which may wane more rapidly in populations with immunosenescence or immature immune systems.

Summary of antigenic targets

Prefusion F protein – central neutralizing target; conserved across RSV‑A and RSV‑B; structural stabilization is a universal design principle.
G protein – supplementary target for attachment inhibition; inclusion augments breadth, especially in infant‑focused formulations.

By aligning the choice of platform with the desired immune profile (e.g., strong humoral immunity for older adults versus combined mucosal‑cellular immunity for infants), developers can tailor RSV vaccines to the specific needs of each vulnerable group while maintaining a focus on the conserved prefusion F epitopes that underpin cross‑protective efficacy.

Immunological mechanisms and correlates of protection

The protective effect of respiratory syncytial virus (RSV) immunization is anchored in the induction of neutralizing antibodies that target the virus‑specific surface glycoproteins, principally the fusion (F) protein in its prefusion conformation and, to a lesser extent, the attachment (G) protein. Stabilization of prefusion F preserves conserved neutralizing epitopes, enabling vaccines across platforms—mRNA, protein subunit, live‑attenuated, and viral‑vector—to elicit high‑affinity antibodies that block viral entry into host cells ^[1]. These antibodies constitute the primary correlate of protection across age groups, with higher titres consistently associated with reduced risk of severe lower respiratory tract disease in infants, older adults, and immunocompromised individuals ^[6] ^[7].

Humoral immunity: prefusion F–focused neutralization

Prefusion F‑based subunit and mRNA vaccines instruct host cells to express the stabilized prefusion antigen, prompting B‑cell maturation and the generation of RSV‑specific IgG that neutralizes the virus before it can fuse with respiratory epithelium.
Maternal immunization (e.g., Pfizer’s Abrysvo) amplifies this response in pregnant individuals, resulting in transplacental transfer of IgG that confers passive protection to the newborn during the first months of life ^[8].
Monoclonal antibody prophylaxis (e.g., nirsevimab) supplies pre‑formed anti‑F antibodies, offering immediate protection without requiring an active immune response ^[9].

Cellular immunity and breadth of protection

While neutralizing antibodies dominate the protective signature, T‑cell responses—particularly CD8⁺ cytotoxic lymphocytes—contribute to viral clearance and may enhance durability of protection. Platforms that deliver antigenic genes via viral vectors or that employ live‑attenuated strains can stimulate endogenous antigen processing, fostering CD4⁺ helper and CD8⁺ effector pathways in addition to humoral immunity. This dual activation is thought to augment protection against divergent RSV genotypes and may mitigate the impact of antigenic drift ^[9].

Age‑specific correlates and immunosenescence

Older adults exhibit immunosenescence, characterized by reduced naïve T‑cell pools, diminished B‑cell repertoire diversity, and chronic low‑grade inflammation (“inflammaging”). Consequently, vaccine formulations for this group often incorporate adjuvants (e.g., AS01E) or higher antigen doses to overcome blunted responses and achieve neutralizing antibody titres comparable to younger cohorts ^[11].
Infants receive protection primarily through passive immunity—maternal antibodies or monoclonal antibodies—because their neonatal immune system is immature and may exhibit interference with active vaccine‑induced responses ^[6].

Correlates of protection in clinical trial design

Recent phase III trials have adopted pragmatic efficacy endpoints (hospitalization, severe lower‑respiratory‑tract disease) that directly reflect the neutralizing antibody threshold required for clinical benefit. Immunogenicity assays measuring palivizumab‑competing antibody titres and microneutralization titres serve as surrogate markers for protection and guide dose selection, especially in populations with heightened risk of waning immunity ^[13]. Longitudinal monitoring of antibody durability informs the need for booster strategies in older adults, where effectiveness declines after 12–18 months ^[14].

Structural considerations for cross‑strain durability

The prefusion F protein’s conserved neutralizing epitopes are less susceptible to antigenic drift than the postfusion form. By stabilizing this conformation, vaccines achieve broad cross‑strain neutralization, including activity against monoclonal‑antibody‑resistant variants ^[1]. Continuous genomic surveillance of the F and G genes informs updates to vaccine immunogens, ensuring that emerging mutations do not erode the neutralizing antibody response ^[16].

Clinical efficacy, safety, and reactogenicity profiles

Clinical development of RSV vaccines has yielded robust evidence of high effectiveness in preventing severe lower‑respiratory‑tract disease, while safety and reactogenicity findings have generally been comparable to those of other routine respiratory vaccines. The data are summarized below for the principal target groups—older adults, pregnant individuals (maternal immunization), and infants receiving passive immunoprophylaxis.

Efficacy in older adults

Large real‑world effectiveness studies in adults aged ≥ 60 years have reported vaccine‑derived protection against hospitalization ranging from 58 % to 92 % during the first RSV season after a single dose, with the highest estimates (≈ 92 %) observed for severe outcomes such as intensive‑care admission and death ^[7] ^[18]. These benefits are achieved with a one‑time administration of either a prefusion prefusion F protein‑subunit formulation or an mRNA platform, both of which elicit strong neutralizing antibody responses.

Waning immunity has emerged as a notable limitation. Analyses of U.S. veteran cohorts showed a measurable decline in effectiveness after the second respiratory season, suggesting that protection may diminish beyond 12 months in the elderly ^[14]. This decline underpins ongoing discussions of booster strategies for individuals with chronic comorbidities or advanced immunosenescence.

Maternal immunization and infant protection

Maternal vaccination during weeks 32–36 of pregnancy (e.g., the Pfizer Abrysvo regimen) generates high maternal neutralizing antibody titres that are transferred across the placenta, providing passive immunity to newborns for the first ~ 6 months of life. While direct infant efficacy data are limited, observational studies indicate a substantial reduction in RSV‑related hospitalizations among infants whose mothers received the vaccine ^[20].

For infants who cannot rely on maternal antibodies (e.g., pre‑term birth), long‑acting monoclonal antibodies such as nirsevimab deliver immediate passive protection. Clinical trials demonstrate ≈ 70 %–75 % efficacy against medically attended RSV infection in the first eight months of life, complementing the maternal‑vaccine strategy and reducing severe disease burden in this high‑risk group ^[20].

Common reactogenicity and safety observations

Across phase III trials and post‑marketing surveillance, the reactogenicity profile of RSV vaccines is characterized by mild to moderate local and systemic events:

Reaction (adults ≥ 60 y)	Frequency
Injection‑site pain	55.9 %
Fatigue	30.8 %
Headache	26.7 %
Chills	11.6 %

These rates are consistent with those observed for seasonal influenza and other respiratory vaccines, and most events resolve within 48 hours ^[22] ^[23]. Serious adverse events (SAEs) have been rare; integrated safety analyses of nearly 47 000 adults receiving bivalent prefusion F vaccines reported SAE frequencies comparable to background rates in the general population ^[24].

Pediatric safety concerns have shaped regulatory vigilance. A phase I trial of a live‑attenuated mRNA candidate was temporarily paused after five cases of severe lower‑respiratory‑tract disease occurred, prompting a thorough evaluation for potential vaccine‑associated enhanced disease—a historically observed risk with early RSV vaccine attempts ^[25]. Subsequent formulations have incorporated prefusion stabilization and rigorous immunogenicity thresholds to mitigate this risk.

Reactogenicity in special populations

Pregnant individuals: Post‑marketing surveillance (e.g., VAERS) has identified a higher proportion of reports classified as serious, with preterm birth being the most frequently cited pregnancy‑specific event. Ongoing disproportionality analyses aim to clarify causal links and guide counseling ^[26].
Immunocompromised adults: Trials emphasize longitudinal monitoring of antibody durability, as immune suppression can blunt both humoral and cellular responses. Tailored dosing schedules and potential booster doses are under investigation to achieve protective titres comparable to immunocompetent cohorts ^[27].

Summary of benefit–risk balance

The accumulated evidence indicates that RSV vaccines provide highly protective efficacy against severe disease in older adults and, through maternal immunization, confer passive protection to infants. Reactogenicity is mild and transient, with serious safety signals being uncommon and closely monitored. Waning immunity and the need for possible boosters, particularly in the elderly, remain active areas of investigation, as does the optimization of maternal‑vaccine timing to maximize transplacental antibody transfer.

Regulatory pathways and approval landscape

The approval process for respiratory syncytial virus (RSV) immunization products has diverged markedly from the pathways traditionally used for routine childhood vaccines because the primary target groups are older adults, pregnant people, and high‑risk infants. These differences have shaped distinct regulatory strategies, post‑marketing commitments, and global harmonisation efforts.

Accelerated and conditional pathways for high‑risk populations

RSV vaccine development has been driven by urgent public‑health needs, prompting the use of accelerated or “de‑risking” review mechanisms. The U.S. FDA granted approval for the maternal vaccine Abrysvo in August 2023 under a pathway that required demonstration of safety and efficacy in pregnant people and proof of trans‑placental antibody transfer to newborns ^[7]. Similarly, protein‑subunit and mRNA candidates for adults ≥ 60 years have been approved on the basis of single‑dose phase III trials that showed high efficacy against severe disease, with the agencies imposing post‑marketing surveillance to monitor long‑term safety and durability ^[7].

In contrast, routine childhood vaccines typically proceed through the full pre‑licensure sequence (phase I–III) and receive standard approval after extensive pediatric safety data are gathered. RSV products, however, often receive conditional approvals after relatively short efficacy follow‑up, with obligations to submit additional data on waning immunity, rare adverse events, and effectiveness in diverse sub‑populations ^[7].

Age‑specific risk‑benefit assessments

Regulators have placed particular emphasis on risk‑benefit analyses for vulnerable groups. For older adults, the benefit of preventing hospitalization and death outweighs the modest reactogenicity observed (injection‑site pain, fatigue, headache, chills) that is comparable to influenza vaccines ^[31]. For pregnant individuals, safety monitoring focuses on maternal‑specific outcomes such as preterm birth, which has been the most frequently reported serious event in the Vaccine Adverse Event Reporting System (VAERS) ^[26]. These assessments inform the Advisory Committee on Immunization Practices (ACIP) recommendations that all adults ≥ 75 years receive a single dose, and that adults 60‑74 years with chronic conditions be offered vaccination ^[7].

Post‑marketing safety and effectiveness surveillance

Because many RSV products were approved with limited long‑term data, regulatory agencies have instituted robust post‑marketing surveillance programs. The United States employs the VAERS and the RSV‑NET to capture serious safety signals and real‑world effectiveness metrics. Data from these systems have shown that vaccine effectiveness against severe outcomes in adults can wane after 12–18 months, prompting discussions about booster strategies for high‑risk seniors ^[14]. Similar vigilance is applied to monoclonal antibody prophylaxis (e.g., nirsevimab) in infants, with safety reporting focused on rare hypersensitivity reactions ^[20].

Global harmonisation and WHO coordination

The disparate national regulatory timelines have created inequalities in product access. The WHO has convened consultations to develop global regulatory pathways that streamline evaluation of RSV vaccines and maternal immunisation products, aiming to align standards for efficacy, safety, and pharmacovigilance across regions ^[36]. WHO‑led market studies also assess demand, pricing, and supply logistics to support equitable distribution, especially in low‑ and middle‑income countries ^[37].

Implications for future regulatory frameworks

The experience with RSV immunisation has highlighted several lessons for future vaccine regulation:

Target‑population‑specific pathways – approvals can be accelerated when the benefit is concentrated in a clearly defined high‑risk group (e.g., adults ≥ 75 years, infants < 8 months).
Conditional licensure with clear post‑marketing milestones – agencies require ongoing data on durability, variant coverage, and rare adverse events.
Integration of molecular epidemiology – real‑time genomic surveillance informs whether vaccine strain updates are needed, mirroring influenza‑like updates.
Universal safety monitoring infrastructure – expanding existing systems (VAERS, RSV‑NET, national pharmacovigilance databases) to capture data across age groups improves confidence and guides policy revisions.

Collectively, these regulatory approaches aim to balance rapid access to life‑saving RSV products with the rigorous safety oversight necessary for vulnerable populations.

Integration into national immunisation programmes

Integrating respiratory syncytial virus (RSV) vaccines into existing national immunisation programmes requires coordinated attention to logistics, economic evaluation, equity, and public‑health communication. Lessons from recent approvals for older adults, pregnant persons, and high‑risk infants have shaped policies that build on established vaccine storage and handling infrastructure while addressing the specific needs of vulnerable groups.

Logistics and cold‑chain requirements

RSV vaccine formulations, like most modern protein‑subunit and mRNA products, must be kept at 2–8 °C from manufacture through administration. Programs can leverage the same cold‑chain network used for influenza, COVID‑19, and routine paediatric vaccines, but must verify that temperature‑monitoring devices are calibrated and that contingency plans exist for power outages or transport delays ^[38]. In remote or resource‑limited settings, mobile cold‑boxes and solar‑powered refrigerators have proven effective for maintaining temperature stability during outreach campaigns.

Cost‑effectiveness and target‑population prioritisation

Economic analyses consistently show that RSV vaccination is cost‑effective when directed at high‑risk groups. For example, adjuvanted RSVPreF3 vaccination in U.S. adults aged 50–59 years with chronic conditions yields favorable cost‑utility ratios, while bivalent RSVPreF vaccines for adults ≥60 years provide substantial health‑care savings by preventing hospitalisation ^[39]. In infants, the long‑acting monoclonal antibody nirsevimab is both clinically effective and cost‑saving when administered before the first RSV season ^[40]. These data support risk‑stratified rollout: routine immunisation for all older adults, targeted maternal vaccination during weeks 32–36 of pregnancy, and prophylaxis for pre‑term or otherwise high‑risk infants.

Equity and access across diverse health‑care settings

Equitable access hinges on eliminating structural barriers that disproportionately affect low‑income and minority populations. In the United States, Black, Hispanic, and American Indian/Alaskan Native communities experience higher RSV‑related hospitalisation rates, underscoring the need for outreach programmes, subsidised vaccine pricing, and inclusion of RSV products in initiatives such as the Vaccines for Children (VFC) programme. Globally, partnerships with Gavi, the Medicines Patent Pool, and the World Health Organization (WHO) are essential to lower purchase costs and facilitate technology transfer for low‑ and middle‑income countries (LMICs) ^[41].

Policy alignment and national guidance

National health authorities have already incorporated RSV vaccines into their immunisation schedules. The United Kingdom extended its programme in 2026 to cover all residents in care homes for older adults and individuals aged 80 years and over, following advice from the Joint Committee on Vaccination and Immunisation (JCVI) ^[42]. In the United States, the Centers for Disease Control and Prevention (CDC) recommends a single dose for adults ≥75 years and for adults 60–74 years with chronic health conditions, administered in late summer or early fall before RSV circulation peaks ^[7]. These recommendations illustrate how regulatory guidance can drive timely integration while allowing flexibility for local epidemiology.

Public‑health messaging and addressing misconceptions

Effective communication is critical to overcome vaccine hesitancy and misconceptions about RSV vaccine novelty or cost. Evidence‑based campaigns that frame RSV alongside familiar respiratory illnesses—such as influenza and COVID‑19—help the public understand its burden and the benefits of vaccination ^[44]. Tailoring messages to specific audiences (pregnant individuals, older adults, caregivers) using microlearning modules, podcasts, and clinician‑led discussions has been shown to improve uptake ^[44]. Transparent reporting of safety data, especially regarding rare adverse events, reinforces trust and supports sustained programme participation.

Surveillance and data‑driven programme optimisation

Robust post‑marketing surveillance systems are required to monitor real‑world effectiveness, safety signals, and durability of protection. In the United States, the RSV Hospitalisation Surveillance Network (RSV‑NET) and the National Respiratory and Enteric Virus Surveillance System (NREVSS) collect detailed data on RSV activity, vaccine coverage, and outcomes, enabling rapid detection of waning immunity or emerging strain variants ^[46]. Similar platforms are being adapted in LMICs to ensure that vaccine impact assessments inform booster‑dose strategies and strain‑update decisions.

Summary of key considerations

Maintain 2–8 °C cold‑chain integrity using existing vaccine logistics infrastructure.
Prioritise high‑risk groups (older adults, pregnant persons, pre‑term infants) to maximise cost‑effectiveness.
Implement equity‑focused measures—subsidies, community‑based delivery, and global partnership‑driven price reductions.
Align national policies with CDC, JCVI, and WHO recommendations, allowing flexibility for local epidemiology.
Deploy targeted public‑health communication that addresses safety concerns and places RSV in the broader context of respiratory disease prevention.
Strengthen surveillance networks to track vaccine impact, inform booster timing, and guide strain selection for future formulations.

By addressing these logistical, economic, equity, and communication pillars, national immunisation programmes can successfully incorporate RSV vaccines, reducing the burden of severe RSV disease across all vulnerable populations.

Cost‑effectiveness, equity, and implementation challenges

RSV vaccine programmes must resolve a triad of economic, access‑related, and operational issues before they can achieve population‑level impact. Evidence from clinical and real‑world studies shows that vaccines for older adults and monoclonal‑antibody prophylaxis for infants can be cost‑saving or cost‑effective when targeted at high‑risk groups, but the magnitude of economic benefit depends on disease burden, vaccine price, and the durability of protection.

Economic evaluations

Older adults – Analyses of adjuvanted protein‑subunit and bivalent prefusion‑F formulations demonstrate favourable cost‑effectiveness for adults ≥ 60 years, especially when restricted to those ≥ 75 years or to 60‑74‑year‑old individuals with chronic conditions. These studies incorporate reduced hospitalization costs, lower intensive‑care utilisation, and the societal value of preventing severe lower‑respiratory‑tract disease ^[7].
Infants and young children – Long‑acting monoclonal antibodies such as nirsevimab have been modelled as cost‑saving in high‑burden settings by averting pediatric hospitalisations and associated intensive‑care costs. Maternal immunisation (e.g., Abrysvo) yields additional economic benefits through passive antibody transfer that protects infants during the first months of life, reducing outpatient visits and emergency‑department presentations ^[20].

These findings support targeted implementation rather than universal rollout, maximizing health‑system savings while limiting expenditures on low‑risk populations.

Equity considerations

Equitable access is jeopardised by several structural and perceptual barriers:

Geographic and socioeconomic disparities – Hospitalisation rates for RSV are markedly higher among Black, Hispanic, and Indigenous communities, yet vaccine uptake in these groups lags behind non‑Hispanic White populations (^[49]). Addressing transportation gaps, providing free or subsidised vaccines, and integrating RSV immunisation into existing maternal‑child health platforms are essential steps.
Cold‑chain requirements – Most RSV vaccines require storage at 2 °C–8 °C throughout manufacture, transport, and administration. Leveraging existing vaccine cold‑chain infrastructure (e.g., influenza and COVID‑19 programs) can reduce marginal costs, but low‑resource settings often lack reliable temperature monitoring, necessitating investments in portable refrigeration and real‑time data loggers.
Misconceptions about safety and cost – Surveys reveal persistent doubts about the novelty of RSV vaccines and overestimation of their price, which dampen demand. Evidence‑based communication that frames RSV alongside familiar respiratory illnesses (influenza, COVID‑19) and highlights the proven safety profile of single‑dose regimens helps counter vaccine hesitancy (^[44]).

Implementation challenges

Programmatic integration – Adding RSV immunisation to national schedules requires coordination with existing adult‑ and maternal‑vaccination visits. In the United Kingdom, the extension of the programme to care‑home residents and adults ≥ 80 years involved a dedicated public‑health campaign and alignment with seasonal influenza clinics (^[42]).
Waning immunity – Real‑world data indicate a decline in vaccine effectiveness after 12 months in older adults, prompting discussions about booster doses for high‑risk subpopulations (^[52]). Cost‑effectiveness models must therefore incorporate the probability of revaccination.
Regulatory and supply‑chain timing – Accelerated or conditional approvals for maternal vaccines and monoclonal antibodies have created staggered availability across regions. Harmonising regulatory pathways and ensuring predictable supply chains are critical to avoid stock‑outs, particularly in low‑ and middle‑income countries where procurement mechanisms differ (^[53]).

Strategies for overcoming barriers

Lever‑aging existing platforms – Incorporating RSV vaccines into the annual influenza or COVID‑19 vaccination campaigns reduces additional visits and maximises the use of established cold‑chain networks.
Subsidies and financing mechanisms – Gavi and the Medicines Patent Pool are negotiating tiered pricing and licensing agreements to lower unit costs for low‑income settings, improving affordability (^[41]).
Community‑based delivery – Mobile vaccination units, pharmacy‑led pilots, and partnerships with trusted local health workers have demonstrated higher uptake in underserved populations, especially when paired with culturally tailored education (^[55]).
Robust surveillance – Expanding systems such as the RSV Hospitalization Surveillance Network (RSV‑NET) and integrating genomic monitoring enable rapid detection of waning effectiveness, emerging variants, and safety signals, informing timely policy adjustments (^[46]).

Key takeaways

Targeted vaccination of high‑risk older adults and infant prophylaxis can be economically justified, but durability of protection and revaccination needs must be factored into long‑term budgeting.
Equitable access hinges on eliminating cold‑chain gaps, subsidising vaccine costs, and confronting misinformation through evidence‑based communication.
Successful implementation requires alignment with existing immunisation infrastructure, flexible delivery models, and continuous surveillance to adapt to waning immunity and viral evolution.

By addressing these cost‑effectiveness, equity, and operational challenges, public‑health authorities can ensure that RSV prevention strategies deliver maximal health benefit across diverse populations.

Surveillance, genomic monitoring, and strain selection

Effective control of respiratory syncytial virus (RSV) hinges on robust surveillance systems that track circulating genotypes, detect antigenic drift, and inform timely updates of vaccine antigens. Contemporary RSV vaccine design focuses on the prefusion conformation of the F protein and, to a lesser extent, the G protein, because these surface glycoproteins harbor the most potent neutralizing epitopes. Continuous monitoring of mutations in these proteins is essential to maintain cross‑protective efficacy across the diverse RSV‑A and RSV‑B lineages that co‑circulate worldwide.

Genomic variability and antigenic drift

RSV’s negative‑sense RNA genome mutates at a moderate but steady rate, driven by the error‑prone RdRp complex. Point mutations—such as the L305I substitution in the prefusion F protein—can remodel key neutralizing epitopes, diminishing antibody binding and vaccine effectiveness ^[57]. Likewise, extensive variation in the G protein, which mediates attachment to host receptors (including CX3CR1), contributes substantially to immune evasion ^[58]. Genome‑wide analyses show that antigenic drift concentrates in these surface proteins, with distinct mutation patterns in RSV‑A versus RSV‑B subtypes ^[16]. These findings underscore why surveillance must prioritize full‑length F and G gene sequencing rather than generic viral detection alone.

Molecular epidemiology and strain‑focused surveillance

Modern molecular surveillance leverages whole‑genome sequencing and phylogenetic reconstruction to map strain circulation at regional and global scales. Studies from Switzerland (2019‑2024) and the United States (2024) illustrate seasonal shifts in dominant genotypes and the emergence of monoclonal‑antibody‑resistant variants, prompting real‑time updates to vaccine composition ^[60]; ^[61]. Such data are integrated into platforms analogous to the influenza GISRS, enabling early detection of novel RSV lineages and informing the selection of strains for bivalent prefusion F vaccine formulations.

Strain selection and vaccine updating strategies

Current vaccine candidates adopt two complementary strategies to address genetic diversity:

Prefusion‑stabilized F protein platforms – By locking the F protein in its antigenically optimal prefusion state, these vaccines elicit broad neutralizing antibodies that retain activity against both contemporary and resistant RSV strains ^[1]. Computational epitope mapping identifies conserved regions less prone to mutation, guiding antigen design that tolerates drift across RSV‑A and RSV‑B.
Multivalent or bivalent formulations – Inclusion of multiple F immunogens, sometimes paired with conserved G epitopes, expands the breadth of coverage. Bivalent prefusion F vaccines have demonstrated neutralization of contemporary circulating strains as well as monoclonal‑antibody‑resistant variants, offering a buffer against rapid antigenic change ^[1].

These approaches are iteratively refined as surveillance data reveal new mutation hotspots. When a significant shift—defined by changes in neutralizing epitope prevalence or emergence of escape mutations—is detected, manufacturers can adjust the antigen composition in subsequent production cycles, akin to the annual reformulation of influenza vaccines.

Public‑health implications of surveillance gaps

Despite advances, several gaps limit the full potential of RSV genomic monitoring:

Geographic disparity in sequencing capacity – Low‑ and middle‑income countries often lack the laboratory infrastructure for high‑throughput viral genomics, creating blind spots in global strain maps.
Inadequate integration with clinical outcome data – Linking genotype information to disease severity and vaccine breakthrough cases is essential for assessing the real‑world impact of drift.
Misconceptions about the need for frequent updates – Some stakeholders incorrectly assume that RSV vaccines require yearly reformulation; current data support a longer interval between updates, provided surveillance confirms antigenic stability.

Addressing these gaps requires investment in decentralized sequencing networks, standardized data‑sharing agreements, and the coupling of genomic data with effectiveness studies across age groups.

Surveillance infrastructure and future directions

National public‑health agencies operate a suite of complementary systems:

RSV Hospitalization Surveillance Network (RSV‑NET) – Captures laboratory‑confirmed RSV hospitalizations, feeding data into genomic analyses ^[46].
National Respiratory and Enteric Virus Surveillance System (NREVSS) – Provides virologic testing trends that trigger deeper sequencing efforts.
New Vaccine Surveillance Network (NVSN) – Focuses on pediatric acute respiratory infections, integrating sequence data with clinical severity metrics.

Future enhancements will include real‑time dashboards that overlay strain prevalence, mutation hotspots, and vaccine‑matched antigenicity, facilitating rapid regulatory decisions on strain updates. Advances in AI‑driven epitope prediction promise to shorten the interval between detection of a drift event and incorporation of the new antigen into vaccine pipelines.

Future directions and research priorities

The rapid expansion of the RSV vaccine portfolio has highlighted several priority areas that must be addressed to ensure durable, cross‑protective protection across all vulnerable groups. Ongoing research is focused on refining antigen design, strengthening molecular surveillance, optimizing immunization schedules for distinct age cohorts, and integrating passive‑immunity strategies with active vaccines.

Optimizing antigenic targets and platform design

Prefusion F protein stabilization – The prefusion conformation of the F protein remains the most potent neutralizing antigen. Stabilized prefusion F immunogens have demonstrated broad activity against contemporary strains and monoclonal‑antibody‑resistant variants, prompting continued refinement of the structural scaffold to preserve key epitopes while tolerating mutational drift ^[1].
Incorporating the G attachment protein – Mutations in the G protein contribute substantially to antigenic drift. Bivalent approaches that present both prefusion F and conserved G domains are being evaluated to broaden strain coverage, especially for RSV‑A and RSV‑B subtypes.
Multivalent and bivalent formulations – Early‑phase studies of bivalent prefusion F vaccines show effective neutralization of both contemporary circulating strains and engineered escape variants, supporting a strategy of including multiple antigenic variants within a single product to pre‑empt future drift.

Addressing waning immunity and durability

Long‑term effectiveness monitoring – Real‑world data indicate that vaccine‑derived protection in older adults declines after roughly 12 months, and similar waning is observed for monoclonal‑antibody prophylaxis after 18 months. Prospective cohort studies are being launched to define optimal booster intervals for adults aged ≥60 years and for high‑risk immunocompromised patients.
Adjuvant and dose optimization – Adjuvanted protein subunit platforms and higher‑dose mRNA formulations are under investigation to counteract immunosenescence and achieve higher, more persistent neutralizing antibody titres in the elderly.

Enhancing molecular epidemiology and strain selection

Genomic surveillance integration – Whole‑genome sequencing of circulating RSV isolates is now being linked to vaccine design pipelines, enabling near‑real‑time detection of amino‑acid substitutions in the F and G proteins that could compromise antibody binding. This approach mirrors influenza‑virus strain‑selection models and informs timely updates to vaccine compositions.
Computational epitope mapping – Machine‑learning algorithms are applied to identify conserved neutralizing epitopes across diverse genotype datasets, guiding the selection of antigen variants that maintain cross‑protective efficacy despite ongoing drift.

Tailoring immunization strategies for specific populations

Maternal vaccination – Ongoing trials of maternal RSV vaccines aim to refine the optimal gestational window (weeks 32–36) to maximize transplacental transfer of high‑titer neutralizing antibodies while confirming safety for both mother and fetus. Immunogenicity correlates in infants born to vaccinated mothers are being compared with those achieved by direct monoclonal‑antibody prophylaxis.
Infant passive immunization – Long‑acting monoclonal antibodies such as nirsevimab continue to be evaluated for extended dosing intervals and for use in infants beyond the first RSV season (up to 24 months) who remain at heightened risk. Combination strategies that pair maternal vaccination with a single monoclonal‑antibody dose are also under study.
Older adult vaccine schedules – Pragmatic phase III trials are testing staggered dosing (single dose versus booster at 12 months) in adults aged ≥75 years and in the 60–74 year cohort with chronic comorbidities, with hospitalization and mortality as primary endpoints.

Overcoming implementation challenges

Cold‑chain logistics – New formulations are being engineered for stability at 2–8 °C to leverage existing vaccine distribution networks, reducing reliance on ultra‑cold storage and facilitating rollout in low‑resource settings.
Cost‑effectiveness and equity – Economic modelling demonstrates that targeting high‑risk older adults and universally offering monoclonal antibodies to infants ≤8 months can be cost‑saving, but equitable access requires coordinated subsidy mechanisms and global partnership agreements (e.g., Gavi, Medicines Patent Pool).
Public‑health communication – Evidence‑based messaging campaigns that contextualize RSV alongside influenza and COVID‑19 have been shown to improve vaccine acceptance, particularly when clinicians are equipped with concise safety and efficacy data for both active and passive immunization options.

Regulatory and global harmonization

Accelerated yet condition‑based approvals – Recent FDA and EMA authorizations for maternal and adult RSV vaccines have incorporated post‑marketing commitments for long‑term safety and effectiveness monitoring. Aligning these pathways internationally will streamline access while ensuring rigorous risk‑benefit assessments for each target group.
Surveillance‑driven updates – Integrated national immunization registries combined with RSV‑NET and similar hospital‑based surveillance platforms are being expanded to capture vaccine impact across age strata, supporting data‑driven decisions on strain reformulation and booster policies.

Collectively, these research priorities aim to close the remaining knowledge gaps—particularly around durability of protection, antigenic drift, and equitable delivery—so that RSV prevention can evolve from a series of siloed interventions into a coordinated, globally harmonized immunization strategy.