Clinical Significance of Rhinoviruses and Progress Toward Vaccination

Abstract

Rhinoviruses (RVs) are the most frequent viral causes of respiratory infections worldwide and contribute substantially to a spectrum of respiratory diseases, including wheezing, asthma, and lower respiratory tract illnesses throughout the lifespan. Despite their substantial disease burden, vaccine development for RVs has been hindered for decades due to extensive serotypic diversity and limited cross-reactive immune responses. However, recent progress in structural virology, immune profiling, and antigen discovery─particularly through peptide array mapping and the identification of conserved neutralizing epitopes─has revived interest in the design of RV vaccines. Novel strategies targeting conserved B cell capsid domains, conserved T cell epitopes, and high-valent vaccine formulations have shown promise in preclinical models. This review summarizes the current understanding of RV infection epidemiology, risk stratification for early vaccine prioritization, and evolving vaccine development strategies, while highlighting critical gaps and the growing scientific momentum toward clinical translation. With continued innovation, RV vaccination may become a viable strategy to mitigate the longstanding and pervasive global health burden of RV infection.

INTRODUCTION

Rhinoviruses (RVs) are among the most prevalent respiratory pathogens worldwide and contribute substantially to both upper and lower respiratory illnesses across all age groups.¹ While often associated with mild cold symptoms, RVs are the leading viral cause of wheezing and asthma in early life and a major contributor to hospitalization and chronic respiratory morbidity in children.²,³ In adults, RV exacerbates underlying conditions, such as asthma, chronic obstructive pulmonary disease (COPD), and bronchiectasis, further amplifying healthcare burden and reducing quality of life.⁴,⁵,⁶ Despite their widespread clinical and socioeconomic impacts, RV vaccines have not yet been licensed.

The virus’s extraordinary antigenic diversity has hindered the development of an effective RV vaccine.⁷ To date, 174 distinct types have been identified among 3 species (RV-A, RV-B, and RV-C), which differ in their capsid structures and receptor usage.⁸ This considerable heterogeneity limits cross-protective immune responses and presents a substantial challenge for immunogen design. Additionally, RV-specific neutralizing antibodies (nAbs) induced by natural infections are typically type specific,⁹ offering little protection against heterotypic infection. Moreover, the limited availability of broadly applicable and immunologically relevant animal models has further constrained preclinical evaluation of vaccine candidates.

Nonetheless, recent advances in structural virology, immune profiling, and vaccine technology have supported sustained efforts toward developing RV vaccines.¹⁰ Promising strategies include the use of subunit antigens targeting conserved viral epitopes, such as those on VP4 or internal proteins, and the development of multivalent formulations covering a broad spectrum of types to enhance cross-serotype immunity.¹¹ Structural insights derived from peptide array mapping and reverse vaccinology are advancing rational RV vaccine design.¹²,¹³

This review summarizes the epidemiology and clinical significance of RV infections, highlights high-risk populations who would most benefit from RV vaccination, and examines recent advances and the remaining barriers in RV vaccine development. As efforts continue, RV vaccination holds promise not only for reducing the burden of common colds and RV-associated wheezing and asthma, but also for preventing or reducing long-term respiratory morbidity in both pediatric and adult populations.

EPIDEMIOLOGY OF RVs

Global burden of RV infection

RVs are ubiquitous worldwide and the leading cause of acute respiratory illnesses in most age groups.¹⁴ Surveillance studies estimate that RVs are detected in approximately half of individuals with acute respiratory illnesses globally, with varying across regions, age groups, and populations.¹⁴,¹⁵,¹⁶,¹⁷ Studies from the New Vaccine Surveillance Network (NVSN) in the US reported that RVs were the most frequently detected viruses among children under 5 years of age hospitalized for acute respiratory illnesses, accounting for up to 25%–35% of detections.¹⁴ In Europe, multicenter surveillance data from Spain, Finland, and the UK similarly found that RVs were the leading viral causes of outpatient and hospitalized respiratory infections in infants and young children.¹⁸,¹⁹ In South Korea, nationwide surveillance of children with community-acquired pneumonia from 2018 to 2020 identified RVs as the most frequently detected respiratory viruses in children with pneumonia, accounting for 29.8% of all illnesses.¹⁶

In adults, RVs are the leading causes of acute respiratory illness worldwide and contribute substantially to the global burden of respiratory infections.²⁰,²¹,²² Epidemiologic studies across multiple regions have reported that RV accounts for a significant proportion of medically attended respiratory infections in adults, including outpatient visits, emergency department visits, and hospitalizations.²³ In addition, RVs have been identified as the frequent causes of severe pneumonia requiring intensive care unit admission, with studies reporting high detection rates and associated mortalities.²² Notably, RV circulation remained high even during the coronavirus disease 2019 (COVID-19) pandemic, highlighting the persistent nature of RV circulation.¹⁴ These findings highlight RVs as globally predominant respiratory viruses, with its sustained circulation during the COVID-19 pandemic, further underscoring its resilience to public health interventions compared to other common respiratory viruses.

RV infections play a critical role in both the development of asthma in early life and the triggering of asthma exacerbations throughout lifespan. Evidence from birth cohort studies and surveillance data has demonstrated that early-life RV-induced wheezing episodes are one of the strongest predictors of subsequent asthma development in children, particularly among those with atopic predisposition.²,³ Moreover, RVs are the most frequent viral triggers of asthma exacerbations in both children and adults, accounting for a substantial proportion of hospitalizations and healthcare utilization related to asthma morbidity.³,⁶,²⁴ Given the substantial contribution of RV to both asthma development and exacerbations, effective RV vaccination strategies have considerable potential to reduce asthma-related morbidity and healthcare burden throughout the lifespan.

Seasonality of RV infections

RVs circulate year-round and are nearly ubiquitous during common cold seasons.¹⁷,²⁵ Interestingly, seasonal peaks differ by climate zone. In temperate regions, two annual peaks are typical: a major peak in fall and a smaller peak in spring.²⁶ In tropical regions, seasonality is less pronounced, with higher RV incidence during cooler dry seasons.²⁷,²⁸ These seasonal trends in RV infections are shaped by viral, environmental, and host factors.²⁴ Young children most readily spread RV infections, and seasonal peaks in the fall and the spring correspond with children returning to school.²⁹,³⁰ Other contributing factors could be cold ambient temperatures³¹ and pollen exposure.³² Both of these exposures can suppress interferon (IFN) responses.³¹,³² In addition to the seasonal peaks of RVs, the capsid structure and absence of a lipid membrane could enhance RVs’ stability under diverse environmental conditions.²⁸

The seasonal distribution of RV serotypes varies across species and study sites. RV-A has been detected consistently throughout the year without a strong seasonal peak, while RV-B peaks in the fall in temperate climate.²⁴,³³ RV-C is also found year-round, although it is most common in the winter.³⁴,³⁵ These serotype-specific seasonal patterns reflect the relatively common seasonal trends in each RV serotype, which may differ from overall RV seasonality patterns due to differences in the relative prevalence of individual RV serotypes across seasons. At any given time, typically 20–30 distinct RV serotypes co-circulate within communities, and approximately 65%–85% of circulating strains are replaced annually, indicating rapid viral turnover.³⁶,³⁷ Despite the rarity of reinfection with the same RV type,⁹ individuals remain highly susceptible to different RV types due to extensive antigenic diversity, reinforcing their persistent circulation and public health impact.²⁴,³⁶ However, long-term surveillance shows that the most prevalent RV types tend to remain prevalent in multiple seasons.³⁴ In summary, RVs are globally endemic viruses and the plethora of types with limited cross-neutralization ensures their continual persistence in human populations. Seasonal patterns of RV types may help guide vaccination strategies, particularly in determining optimal timing for immunization.

DETERMINANTS OF SUSCEPTIBILITY TO RV INFECTION AND ILLNESS

Susceptibility to RVs is shaped by a dynamic interplay of viral, host, and environmental factors which are often interrelated (Fig. 1). Understanding the determinants of RV infections and illnesses is critical for identifying populations most likely to benefit the most from RV vaccination, particularly in the context of asthma prevention and targeted therapeutic strategies.

Fig. 1. Viral and environmental factors involving susceptibility to rhinovirus infections and illnesses. This illustration summarizes the major viral and environmental factors and their interactions that contribute to susceptibility to RV infection and illness. The major group of RV-A serotypes utilizes ICAM-1 as the entry receptor, whereas the minor group of RV-A serotypes utilizes LDLR.

RV, rhinovirus; ICAM-1, intercellular adhesion molecule-1; LDLR, low-density lipoprotein receptor; CDHR3, cadherin-related family member 3.

Viral factors

The clinical significance and severity of RV infections vary by species,³⁸ with RV-A and RV-C more frequently associated with severe respiratory illnesses, including lower respiratory tract infections, wheezing, and asthma exacerbations, than RV-B.³⁹,⁴⁰,⁴¹,⁴² RV-C is a major cause of lower respiratory tract illnesses, such as wheezing, which are especially common in young children.³⁴,⁴³,⁴⁴,⁴⁵ RV-A is associated with asthma exacerbations, lower respiratory tract infections, and hospitalizations, especially in older children and adults.³⁴,⁴³,⁴⁶ In contrast to the other two RV species, RV-B is typically associated with milder upper respiratory tract infections and is less frequently detected in ill children.³⁸ Recurrent RV-induced wheezing episodes in early life significantly increase the risk of developing asthma, especially in atopic children.³,⁴⁷,⁴⁸

Expression of species-specific receptors for cellular entry of RVs is a key determinant of cellular susceptibility to RVs. The major group of RV-A and all RV-B serotypes binds to intercellular adhesion molecule-1 (ICAM-1), while the minor group of RV-A utilizes the low-density lipoprotein receptor (LDLR).⁴⁹ In contrast, RV-C employs cadherin-related family member 3 (CDHR3),⁵⁰ which is selectively expressed on ciliated airway epithelial cells.⁵¹ The receptor specificity of each species is involved in viral attachment, entry, and infectivity. In addition to differences in receptor usage, RV species also vary in their ability to modulate innate antiviral responses. RV-C inhibits airway epithelial cell type I and III IFN responses, which may facilitate immune evasion and enhance viral persistence.⁵² These species-specific virologic properties contribute to variability in infection susceptibility and may also underlie differences in clinical outcomes.

Host factors

Several host factors are associated with an increased susceptibility to RV infections and illnesses. These include age, genetic variation, allergy, and the quality of antiviral immune responses. Infants and preschool children bear a large share of the RV-related illness burden. They not only contract RVs frequently but are also more likely to develop lower respiratory tract involvement from RV infections that would otherwise be mild in healthy adults.³⁰ The prevalence of RV-C infection declines with age.³⁴ This decline parallels a progressive increase in serum nAbs against RV-C, suggesting age-related acquisition of protective immunity.³⁴ RV wheezing illnesses in early life can mark the beginning of a trajectory toward recurrent wheezing and chronic childhood asthma.⁴⁶

At the other end of the age spectrum, older adults can experience substantial morbidities due to RV infections, including hospitalizations for lower respiratory tract complications as well as increased short- and long-term mortality that is comparable to or even greater than those due to influenza.⁵³ Furthermore, underlying conditions, including immunosuppression, chronic lung disease, and advanced age, also significantly increase susceptibility to RV infections, often leading to severe or prolonged illnesses.⁵⁴,⁵⁵

A missense variant in CDHR3 (rs6967330; C529Y) enhances the epithelial expression of CDHR3 on ciliated airway epithelial cells, facilitating RV-C binding and replication.³⁴,⁵⁶ It is associated with more frequent and severe RV-induced wheezing as well as with an increased risk of developing childhood asthma.⁵⁶,⁵⁷,⁵⁸ In adults with chronic rhinosinusitis, the CDHR3 rs6967330 minor allele was linked to the exaggerated production of both type 2 cytokines (interleukin [IL]-4, IL-5, and IL-13) and antiviral cytokines (IFN-β and IL-10) in response to RV-C exposure in the epithelial cells, along with suppressed Toll-like receptor (TLR)-mediated signaling.⁵⁹ These immune alterations may impair antiviral defense mechanism and promote secondary inflammation or bacterial infections.

Polymorphisms in GSDMB at the 17q21 asthma susceptibility locus can also promote epithelial expression of gasdermin B, which can trigger pyroptosis in response to viral stimuli.⁶⁰,⁶¹ This inflammatory cell death may exacerbate airway damage and amplify RV infection-induced immune responses, particularly in genetically predisposed individuals. Notably, CDHR3 and GSDMB variants may have combined effect to heighten IL-17A responses and increase the risk of asthma following RV infections, without necessarily affecting infection frequency.⁶²

In addition to genetic predisposition, dysregulated antiviral immune responses could promote RV-induced asthma exacerbations. These exacerbations have been linked to low baseline IFN levels, followed by an exaggerated IFN surge after RV infections.⁶³ In asthmatic children, the reduced production of epithelial IFN-β and IFN-λ following RV infections could lead to enhancing viral replication and inflammation with decreased pulmonary function.⁶³,⁶⁴

Atopic predisposition is a major determinant of RV-induced wheezing and asthma.³ Early-life RV-induced wheezing combined with early allergen sensitization is the strongest predictor of asthma development in children with a parental history of allergic diseases.²,³ In addition, high levels of dust mite-specific immunoglobulin (Ig)E significantly increase the risk of RV-induced wheezing in asthmatic children.⁴¹ Treating childhood allergic asthma with omalizumab, which neutralizes IgE-mediated inflammation, reduces susceptibility to RV infections and illnesses as well as virus-induced exacerbations of asthma.⁴⁰,⁶⁵ RV infections can increase epithelial cell alarmin concentrations and T2 inflammation, thereby enhancing pro-asthmatic inflammation.⁶⁶,⁶⁷

Environmental factors

Environmental factors, including climate, the airway microbiome and exposure to air pollution or tobacco smoke, can influence RV infection susceptibility and severity. Cooler temperatures (~33°C), typical of the nasal cavity, can impair RIG-I-like receptor (RLR)-mediated IFN responses in airway epithelial cells, facilitating RV replication compared to core body temperature (37°C).²⁷ The expression levels of ICAM-1, an epithelial cellular receptor for most RV-A and all RV-B serotypes, can be upregulated by environmental stimuli, such as air pollutants, and cigarette smoke.⁶⁸ These conditions may enhance viral attachment, entry, and replication.

The airway microbiome is a key environmental factor modulating host responses to RV infections and its clinical consequences. A Moraxella-dominant airway microbiota has been linked to symptomatic RV infections, more severe wheezing, and increased asthma risk, whereas a commensal-rich microbial profile, particularly enriched in Dolosigranulum and Corynebacterium, is associated with asymptomatic infection, lower viral loads, and potential protection.⁶⁹ In a prospective cohort study, RV infection in the Moraxella-dominant airway microbiota, along with upregulated SMAD3-related epithelial transcriptional activity, was associated with a significantly increased risk of post-infection asthma exacerbations.⁷⁰ These findings support the airway microbiome as a critical modulator of RV-related wheezing or asthma risk.

Integrated factors

Integrated omics studies have identified that integrated factors are endotypes at high-risk for asthma by combining information on RV species, the airway microbiome, host genetic susceptibility, and immune response patterns. In a previous study that an endotype defined by RV-A or RV-C infection, Haemophilus-dominant airway microbiota, and high asthma polygenic risk had a significantly increased risk of asthma by age 6.⁷¹ This group exhibited enhanced type I/II IFN and IL-6–JAK–STAT3 signaling along with predominant neutrophilic inflammation, suggesting a non–type 2 immune features in RV infection-associated asthma.⁷¹ Another study identified a distinct endotype of infants with RV-C bronchiolitis, atopic features (e.g., elevated type 2 cytokines, eosinophilia, and IgE sensitization), and Moraxella predominance, which conferred the highest risk of recurrent wheezing and early childhood asthma by age 5.⁷²

POTENTIAL CANDIDATES FOR FUTURE RV VACCINE IMPLEMENTATION

Priority populations for future RV vaccine implementation include individuals with heightened susceptibility to RV-related morbidity based on genetic, clinical, and immunologic risk factors (Fig. 2). Given that RV-C tends to cause clinically significant illnesses in early life, individuals carrying the CDHR3 rs6967330 variant, particularly infants, represent a key target population for vaccination due to their heightened susceptibility.³⁴,⁷³ In addition, individuals carrying GSDMB risk alleles could be prioritized for RV vaccination due to their vulnerability to RV-triggered asthma exacerbations.⁶¹ Infants and young children with recurrent wheezing and atopic features, including eosinophilia, allergen sensitization, a family history of allergic diseases, or coexisting allergic conditions such as atopic dermatitis, are at increased risk of persistent wheeze and asthma development.³ Regardless of age, patients with allergic asthma represent a high-risk group due to impaired antiviral immunity and the strong association between RV infection and exacerbation.

Fig. 2. Schematic illustration of target populations for future RV vaccine implementation throughout the lifespan. Vulnerable populations include genetically susceptible infants and children with recurrent wheeze and atopic features, those with chronic respiratory diseases, chronic rhinosinusitis, immunocompromised patients, and the elderly.

RV, rhinovirus; CDHR3, cadherin-related family member 3; COPD, chronic obstructive pulmonary disease; GSDMB, gasdermin B.

The CDHR3 rs6967330 risk allele has also been associated with an increased risk of chronic rhinosinusitis,⁷⁴ highlighting this population as another potential target for RV vaccination. Patients with chronic respiratory diseases, such as COPD and bronchiectasis, are also vulnerable, as RV frequently triggers exacerbations.⁴,⁷⁵ Finally, immunocompromised individuals and older adults are prone to severe RV-related outcomes due to immunosenescence and comorbidities.⁴⁶ Strategically targeting high-risk populations for RV vaccination could reduce RV-related disease burden and maximize clinical impact across the lifespan.

RV VACCINE APPROACH

Rationale for the development of RV vaccines: Lessons from the development of respiratory syncytial virus vaccine

Respiratory syncytial virus (RSV) is the leading viral cause of hospitalization for lower respiratory tract illnesses in infants and is associated with an increased risk of recurrent wheezing and long-term respiratory morbidity.⁷⁶ These impacts have made RSV a major focus of vaccine development for decades. Only recently have these efforts borne fruit; in 2023, the first RSV vaccines based on adjuvanted prefusion F protein were approved for use.⁷⁷ Vaccines are now available for older adults and for pregnant women to confer protection to newborns, and a long-acting monoclonal antibody is approved for infants.⁷⁷,⁷⁸ These breakthroughs followed decades of challenges, including the failure of the formalin-inactivated RSV vaccine in the 1960s,⁷⁹ but ultimately succeeded due to advances in structure-based antigen design, particularly stabilization of the F glycoprotein in its prefusion conformation.⁸⁰ The success of RSV vaccine development offers not only a scientific roadmap but also renewed optimism for vaccines targeting other respiratory viruses. With RSV prevention being a reality, attention is shifting to developing vaccine strategies for RV, another major contributor to childhood wheezing and asthma throughout the lifespan.

Immunogenic targets and platforms for the development of RV vaccines

The extensive antigenic and genetic diversities of RVs have posed major challenges to vaccine development, prompting efforts to identify conserved immunologic targets and to evaluate diverse vaccine platforms. Representative approaches and supporting studies are summarized in Table.⁸¹,⁸²,⁸³,⁸⁴,⁸⁵,⁸⁶,⁸⁷,⁸⁸,⁸⁹,⁹⁰,⁹¹,⁹²,⁹³,⁹⁴,⁹⁵,⁹⁶

Table. Summary of studies and strategies in RV vaccine development.

Studies		Year	Vaccine type	Advantages	Disadvantages
Inactivated vaccine
	Doggett et al.86	1963	Live (nasal/oral) & formalin-inactivated RV (intramuscular)	- Live (intramuscular): Strong homotypic nAb response (average, 65-fold titer rise), no illness	- Live (nasal): Caused cold symptoms in some participants
				- Formalin-inactivated: Induced antibodies without causing symptoms	- Live (oral): No infection or antibody rise
					- Formalin-inactivated: Lower titer rise (average, 22-fold)
					- Limited cross-protection specific to the same serotype
	Mitchison et al.87	1965	Formalin-inactivated single serotype	- Partial protection against same serotype	- No heterologous protection
	Perkins et al.88	1969	Intranasal inactivated RV13	- Induced both serum and nasal nAbs; protection against homologous challenge; nasal IgA correlated with protection	- No cross-protection; intramuscular route ineffective despite serum antibody induction
	Douglas et al.89	1972	Subcutaneous inactivated RV13	- Some nAb response	- Minimal in vivo protection
	Hamory et al.90	1975	10-valent inactivated vaccine	- Induced antibody responses to ~30% of included antigens	- Low immunogenicity for several antigens
				- Safe; minimal side effects	- Inconsistent heterologous responses
					- Low viral titers per strain
	McLean et al.81	2012	Inactivated RV1B	- Induced strong IgG responses targeting VP1	- Cross-neutralization limited to closely related serotypes
				- Generated cross-serotype reactive antibodies after repeated exposure	- No in vivo protection tested
				- Freund’s adjuvant enhanced neutralizing titers	- IgA response weak or absent without repeated infection
	Lee et al.82	2016	50-valent inactivated vaccine	- Induced nAbs to 49 of 50 RV-A types in macaques	- Type-specific (not cross-neutralizing)
				- Immunogenicity maintained despite high valency	- Requires high input antigen dose per strain
				- Proof-of-concept for large-scale polyvalent formulation	- Excluded RV-C serotypes
Subunit vaccines
	McCray et al.91	1987	VP1 & VP3 peptides	- Cross-neutralized ~60% of tested serotypes	- Low neutralizing titers
				- Targeted conserved capsid epitopes	- No protection data in humans
				- Potential for broadly protective peptide vaccine
	Katpally et al.84	2009	VP4 peptide	- Induced cross-serotypic nAbs	- Efficacy only shown in vitro
				- Recognized multiple RV types (RV14, RV16, RV29)	- Immunogenicity highly dependent on peptide length/structure
				- Targeted highly conserved VP4 N-terminus	- No in vivo data or challenge model
	Edlmayr et al.83	2011	Recombinant VP1	- Induced strong IgG responses in rabbits and mice	- No in vivo protection data
				- Demonstrated cross-neutralization against multiple RV serotypes	- Cross-neutralization varied by serotype
				- Whole VP1 more effective than peptide-based antibodies
	Glanville et al.92	2013	Recombinant VP0	- Induced systemic and mucosal Th1-skewed CD4⁺ and CD8⁺ T cell responses	- Cross-neutralization breadth limited
				- Generated memory T cells and promoted rapid viral clearance	- Protection observed mainly against tested serotypes
				- Elicited antibodies and T cells with partial cross-reactivity across RV serotypes
	Narean et al.93	2019	Recombinant VP0 (VP4+VP2)	- Identified IgG-binding epitopes in the VP2 NIm-II region	- NIm-II is highly variable among serotypes
				- Cross-reactive antibody responses across RV-A serotypes	- Cross-neutralization not clearly linked to epitope binding
					- Requires live virus for strong neutralizing response
	Niespodziana et al.94	2022	Recombinant fusion proteins with mapped VP1/VP2 epitopes (RV-A89)	- Identified conserved neutralizing epitopes across VP1/VP2	- Protection only for RV-A89
				- Induced nAbs with recombinant peptide–carrier fusion proteins	- No in vivo protection
				- Cross-strain epitope homology with RV2 and RV14	- Lower neutralizing titers than whole-virus antisera
T cell-based vaccines
	Gaido et al.85	2016	Mapped synthetic peptides derived from VP1 (RV-A34, RV-C3) for CD4⁺ T-cell stimulation	- Identification of immunodominant, species-specific CD4⁺ T-cell epitopes from RV-A and RV-C	- No recombinant protein or peptide vaccine tested in vivo
				- Broad HLA class II recognition across diverse donors	- No demonstration of protective immunity
				- Basis for rational design of T-cell based vaccines	- Limited to in vitro T-cell proliferation assays only
	Gomez-Perosanz et al.95	2021	In silico–selected and experimentally validated conserved CD4 T cell epitopes (VP4, VP2, non-structural proteins) from RV-A and RV-C	- Identified 7 conserved, promiscuous CD4 T cell epitopes with broad HLA-II binding	- No in vivo protection data
				- Demonstrated IFN-γ responses in 97% of donors (CD4) and 80% (CD8)	- Not tested in vaccine platform
				- High predicted population coverage (up to 98%)	- Human cohort limited to Caucasian donors
Live attenuated vaccines
	Blanco et al.96	2014	Live RV16 (intramuscular); also evaluated passive and maternal antibody protection	- Strong protection via intramuscular immunization with live RV16	- No cross-serotype protection tested
				- Effective maternal and passive antibody transfer	- UV-inactivated virus failed to protect
				- Established novel cotton rat model for RV vaccine testing	- Limited to RV16 challenge

RV, rhinovirus; nAb, neutralizing antibody; Ig, immunoglobulin; VP, viral protein; CD, cluster of differentiation; HLA, human leukocyte antigen; UV, ultraviolet.

Inactivated vaccines

Early attempts at RV vaccines in the 1960s–1970s used formalin-inactivated whole viruses.⁹⁷ In a pivotal human challenge study, the intranasal administration of a formalin-inactivated RV-13 vaccine induced both serum and nasal nAbs as well as significantly reduced illnesses following viral challenge, despite not preventing the infection itself.⁹⁷ These early findings highlighted the potential of mucosal delivery routes to elicit local IgA-mediated protection.⁹⁷ However, these vaccines targeted only a few serotypes.⁹⁷ One trial in 1975 tested an admixture of 10 serotypes, although it failed to produce broad protection, partially due to insufficient antigen doses and lack of an adjuvant. In a murine model, ultraviolet-inactivated RV1B formulated with Freund’s adjuvant induced homologous nAbs and low-level cross-neutralization against RV-16, supporting the potential of inactivated vaccines to elicit type-specific and limited cross-reactive humoral responses⁸¹ A highly multiplexed RV vaccine, containing 50 inactivated RV-A types, was formulated and tested in rhesus macaques.⁸² Using a prime-boost regimen with an alum adjuvant, this vaccine induced robust nAb responses against 49 of the 50 serotypes.⁸² These findings prove the concept that highly multivalent inactivated vaccines are technically feasible and capable of eliciting broad type-specific immunity in preclinical models.⁸²

Subunit vaccines

Rather than the whole virus, subunit vaccines utilize purified viral proteins or peptide fragments to elicit an immune response. RVs are non-enveloped RNA viruses with icosahedral capsids composed of VP1–VP4 structural proteins.⁹⁸ VP1, VP2, and VP3 form the outer surface and harbor most neutralizing epitopes, while VP4 is internal but transiently exposed during virus entry.⁹⁹ Antigenic variability across more than 170 RV types is driven by sequence diversity in VP1, VP2, and VP3, limiting cross-nAb responses.⁹⁸ VP1, the largest capsid protein and receptor-binding domain, is highly variable and immunodominant.

For RV, subunit vaccine development has largely focused on capsid proteins, particularly VP1. Recombinant VP1 protein, when administered as a subunit vaccine with adjuvant, can induce type-specific IgG and nAb responses in animal models, including RV1B, RV89, and RV14, supporting its potential as an immunogen.⁸³ However, the breadth of cross-reactivity was limited due to the high antigenic variability among serotypes.⁸³ A distinct subunit approach has targeted the N-terminal region of VP4, a normally internal capsid protein that becomes transiently exposed during viral entry or capsid uncoating.⁸⁴ This region harbors relatively conserved sequences across serotypes and may serve as a broadly immunogenic target.⁸⁴ Antibodies raised against a 30-residue synthetic VP4 peptide neutralized the homologous RV-B14 strain and also exhibited cross-neutralization against RV-A16 and RV-A29.⁸⁴ These findings suggest that even conserved, buried epitopes can serve as effective vaccine targets when appropriately presented. Bioinformatics analysis of 100 RV serotypes (75 RV-A and 25 RV-B) has identified VP4 as the most conserved among all capsid proteins, showing over 97% identity across many serotype pairs and containing several predicted B-cell epitopes, which support its potential as a broadly applicable vaccine antigen.¹¹ VP2 also showed epitope potential, whereas VP1 exhibited lower sequence conservation across types.¹¹ Despite these promising leads, subunit vaccines alone often exhibit low immunogenicity and may require strong adjuvants or optimized delivery platforms. Additionally, achieving broad protection is likely to require the inclusion of multiple conserved epitopes spanning diverse RV serotypes to overcome the extensive antigenic diversity of the virus.

T cell-based vaccines

T cell-based strategies have been explored as a complementary approach to address the limited cross-protection of antibody responses.¹⁰⁰ CD4⁺ T cells targeting conserved epitopes in structural and non-structural proteins (e.g., 2C and 3C) can elicit Th1-skewed responses and cross-reactivity across genotypes.⁸⁵,⁹⁸,¹⁰¹ However, while such responses may reduce viral shedding, their correlations of pre-existing T cell responses with clinical outcomes are modest.¹⁰² Similar observations in influenza models further suggest that T cell immunity alone may not sufficiently improve symptom burden or prevent infection.¹⁰³ In a controlled human influenza challenge trial, administration of a vaccine designed to elicit T cell responses against conserved internal antigens failed to reduce viral load or symptom severity.¹⁰³ Moreover, no correlations were observed between the magnitude of T cell responses and clinical outcomes, such as viral shedding, symptom scores, and the incidence or duration of influenza-like illnesses.¹⁰³ While conserved T cell epitopes may support broader vaccine-induced immunity, their clinical relevance remains to elucidated.

Live attenuated vaccines

Live attenuated RV vaccines use a weakened virus that can replicate in the airway and induce protective immunity without causing symptomatic respiratory and allergic manifestations. To date, no live-attenuated RV vaccine has been developed, and traditional attenuation methods, such as cold adaptation, remain largely unexplored. However, advances in reverse genetics have introduced new possibilities for rational attenuation strategies, including targeted deletions of virulence genes, mutations in protease regions,¹⁰⁴ modification of the 5′ untranslated region, such as the internal ribosome entry site,¹⁰⁵ or codon deoptimization strategies that reduce viral protein translation without compromising antigenicity.¹⁰⁶ RV-B viruses are inherently less virulent³⁴,¹⁰⁷ and could provide clues for making attenuated RV strains suitable for vaccination. It remains to be determined whether live attenuated vaccines could produce broad immunity against multiple RV types.

Virus-like particles (VLPs)

VLPs are non-infectious, self-assembled structures composed of viral structural proteins that mimic the native virus but lack genetic material, thus posing no risk of replication.¹⁰⁸ While RV VLPs remain largely conceptual, a multivalent VLP vaccine platform has been proposed and inspired by the success of the 9-valent human papillomavirus vaccine,¹⁰⁹ which targets a similarly non-enveloped virus with an icosahedral capsid. This structural similarity suggests that RV capsid proteins may be amenable to VLP formation, leveraging their repetitive and surface-exposed architecture to stimulate robust B-cell activation. A panel of RV VLPs representing distinct immunotypes could potentially be assembled into a broadly protective formulation.¹⁰⁸ VLPs have the added advantage of presenting antigens in their native structural context, thereby enhancing immunogenicity, especially when combined with adjuvants. However, the feasibility of producing, assembling, and stabilizing a large number of structurally diverse RV VLPs remains a significant technical challenge. To date, no published studies have demonstrated successful VLP formation, immunogenicity, or protective efficacy specifically for RV. However, VLP-based approaches have been explored in other picornaviruses. Notably, VLP vaccines targeting enterovirus A71 have demonstrated robust immunogenicity and protective efficacy in preclinical models,¹¹⁰ offering a promising proof of concept for the potential applicability of VLP-based approaches in RV vaccine development.

Hybrid platforms

Each vaccine platform offers their distinct advantages and limitations. Inactivated and VLP-based vaccines primarily induce antibody-mediated immunity, targeting viral neutralization at the point of entry. In contrast, T cell-based vaccines are designed to promote cross-serotype protection by recognizing conserved viral antigens. The combination of a multivalent inactivated or VLP vaccine to elicit serotype-specific nAbs and components that enhance T-cell responses to conserved epitopes could provide optimal immunity, but it presents considerable conceptual and manufacturing challenges. Advances in modern vaccinology, including structure-based antigen design, epitope mapping, and next-generation adjuvants, may help address the challenges of RV vaccine development.

CHALLENGES IN THE DEVELOPMENT OF RV VACCINES

Multiple challenges, reflecting the virus’s biological complexity and immunologic evasion strategies, have hampered the development of a safe and effective vaccine against RVs.

Antigenic diversity of RV: Implications for vaccine design

A major challenge in developing a broadly effective RV vaccine is the virus’s extensive antigenic diversity, particularly in capsid proteins VP1, VP2, and VP3, which limits cross-serotype neutralization.¹¹¹ While ultra-polyvalent formulations have shown promise,⁸² expanding coverage to include all clinically relevant types, especially RV-C, presents technical and manufacturing challenges.⁹ Although conserved regions like the VP4 N-terminus offer potential for cross-type immunity,⁸⁴ their suboptimal immunogenicity necessitates improved antigen design.

Recent profiling of maternal and infant antibody responses to RV-A16, B52, and C11 has revealed consistent reactivity not only to surface-exposed sites, but also to conserved internal epitopes, including the RV-C VP1 C-loop.¹¹² These findings underscore the potential of targeting naturally immunogenic and conserved regions beyond conventional surface-neutralizing epitopes. Coordinated induction of both humoral and T cell responses may ultimately be required for broad and durable protection.

Potential weak and transient immunity: Insights from natural RV infection

Natural RV infection induces nAbs that are generally serotype specific and of variable duration.⁹ Memory T-cell responses are detectable, but they show variable correlation with protection and are still poorly defined in terms of their longevity and breadth. Unlike infections with viruses, such as measles or influenza, which typically confer long-lasting immunity, RV-induced responses tend to be transient, complicating vaccine design.

Lack of applicable and reproducible animal models

The majority of RV serotypes utilize human-specific receptors, ICAM-1 for major-group RV-A and RV-B as well as CDHR3 for RV-C, which are not naturally expressed in mice, rendering conventional mouse models largely non-permissive.¹¹³ While the minor group of RV-A serotypes, such as RV-1B, can infect mice via LDLR, it causes limited viral replication and represents only a fraction of the viral diversity. Transgenic mouse models expressing human ICAM-1¹¹³ or CDHR3¹⁰ have been developed, with similarly limited viral replication.

Lack of correlates of protection

A major obstacle in RV vaccine development is the absence of clearly defined immune correlates of protection.¹¹⁴ It remains unclear which immune responses are required for cross-serotype efficacy, including humoral, mucosal, and cellular immunity. Although antibodies may act through diverse mechanisms, such as blocking receptor binding, inducing virion aggregation, or promoting intracellular degradation,¹¹⁵ their protective capacity varies depending on the targeted epitope and structural context. Neutralizing antibody can be detected and quantified by assessing inhibition of infectivity measured by reductions in plaque-forming units or increases in viral RNA measured by reverse transcription-polymerase chain reaction.⁹ This is laborious given a large number of clinically important types. Advances in microarrays or virus-specific T cell responses can improve methods for assessing nAb and vaccine efficacy.

CURRENT ADVANCES AND FUTURE PERSPECTIVES

Although no RV vaccine is currently available for clinical use, next-generation approaches are emerging to overcome longstanding obstacles. Building on recent progress in RV structural biology and immunology, research efforts are increasingly focused on identifying conserved capsid regions and epitope profiles that can inform broad immunity. A major innovation area involves using high-resolution peptide array technology to map linear epitope landscapes across diverse RV serotypes.¹¹²,¹¹⁶,¹¹⁷ By systematically tiling peptides that span key capsid proteins, peptide arrays enable the identification of conserved and surface-exposed regions that may be targeted by broadly nAbs. This strategy enables us to pinpoint immunogenic domains within structurally constrained areas of the RV capsid that are less prone to antigenic drift.

To interpret the high-dimensional immunologic data obtained, including peptide-specific binding intensities across multiple RV types and analytical methods, such as Uniform Manifold Approximation and Projection, can visualize and cluster immune reactivity patterns. Reactivity to array peptides across diverse serotypes helps define immunodominant regions with potential for cross-neutralization. These observations inform us about rational antigen selection for engineered immunogens, including multivalent or mosaic constructs. These technologies represent a shift from traditional empirical approaches toward data-driven RV vaccine development. Accelerating advances in structural mapping, high-throughput immunoprofiling, and computational epitope discovery, has renewed optimism that a broadly protective RV vaccine is possible.¹¹⁸,¹¹⁹,¹²⁰

As RV vaccine candidates continue to advance in preclinical research, translation to clinical use will require the establishment of robust immune correlates of protection, identification of high-risk populations as key targets for vaccination, and careful consideration of outcome measures that reflect both infection and RV-associated morbidity. The development of RV vaccines offers a direct opportunity to reduce RV-related disease burden and serves as a platform for advancing vaccine technologies that may be rapidly adapted to address future emerging viral threats.

CONCLUSION

RVs remain a major, unmet challenge in respiratory health, contributing substantially to a wide spectrum of illnesses throughout the lifespan, including wheezing, asthma development/exacerbations, and COPD exacerbations. Despite decades of investigation, no licensed RV vaccine exists, primarily due to the virus’s extensive antigenic diversity and the lack of durable, cross-protective B-cell immunity. However, recent advances, including the identification of conserved neutralizing epitopes, the development of polyvalent and species-specific vaccine candidates (e.g., RV-C), and structural insights into receptor interactions, have revitalized vaccine development efforts. Innovative tools, including peptide array profiling and computational epitope mapping, are accelerating the design of rational immunogens. In the early phases, vaccine strategies must focus on high-risk populations and be designed to achieve clinical outcomes that reduce the severity of RV-associated respiratory illnesses. With sustained scientific momentum, a safe and effective RV vaccine is indeed within reach and has the potential for broad public health impact.