Efficacy, immunogenicity and safety of respiratory syncytial virus prefusion F vaccine: systematic review and meta-analysis.

OBJECTIVE: A notable research gap exists in the systematic review and meta-analysis concerning the efficacy, immunogenicity, and safety of the respiratory syncytial virus (RSV) prefusion F vaccine. METHODS: We conducted a comprehensive search across PubMed, Embase, the Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov to retrieve articles related to the efficacy, immunogenicity, and safety of RSV prefusion F vaccines, published through September 8, 2023. We adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. RESULTS: A total of 22 randomized controlled trials involving 78,990 participants were included in this systematic review and meta-analysis. The RSV prefusion F vaccine exhibited a vaccine effectiveness of 68% (95% CI: 59-75%) against RSV-associated acute respiratory illness, 70% (95% CI: 60-77%) against medically attended RSV-associated lower respiratory tract illness, and 87% (95% CI: 71-94%) against medically attended severe RSV-associated lower respiratory tract illness. Common reported local adverse reactions following RSV prefusion F vaccination include pain, redness, and swelling at the injection site, and systemic reactions such as fatigue, headache, myalgia, arthralgia, nausea, and chills. CONCLUSIONS: Our meta-analysis suggests that vaccines using the RSV prefusion F protein as antigen exhibit appears broadly acceptable efficacy, immunogenicity, and safety in the population. In particular, it provides high protective efficiency against severe RSV-associated lower respiratory tract disease.

Respiratory syncytial virus vaccination during pregnancy for improving infant outcomes.

BACKGROUND: Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections (LRTIs) in infants. Maternal RSV vaccination is a preventive strategy of great interest, as it could have a substantial impact on infant RSV disease burden. In recent years, the clinical development of maternal RSV vaccines has advanced rapidly. OBJECTIVES: To assess the efficacy and safety of maternal respiratory syncytial virus (RSV) vaccination for preventing RSV disease in infants. SEARCH METHODS: We searched Cochrane Pregnancy and Childbirth's Trials Register and two other trials registries on 21 October 2022. We updated the search on 27 July 2023, when we searched MEDLINE, Embase, CENTRAL, CINAHL, and two trials registries. Additionally, we searched the reference lists of retrieved studies and conference proceedings. There were no language restrictions on our searches. SELECTION CRITERIA: We included randomised controlled trials (RCTs) comparing maternal RSV vaccination with placebo or no intervention in pregnant women of any age. The primary outcomes were hospitalisation with clinically confirmed or laboratory-confirmed RSV disease in infants. The secondary outcomes covered adverse pregnancy outcomes (intrauterine growth restriction, stillbirth, and maternal death) and adverse infant outcomes (preterm birth, congenital abnormalities, and infant death). DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods and assessed the certainty of evidence using the GRADE approach. MAIN RESULTS: We included six RCTs (25 study reports) involving 17,991 pregnant women. The intervention was an RSV pre-F protein vaccine in four studies, and an RSV F protein nanoparticle vaccine in two studies. In all studies, the comparator was a placebo (saline, formulation buffer, or sterile water). We judged four studies at overall low risk of bias and two studies at overall high risk (mainly due to selection bias). All studies were funded by pharmaceutical companies. Maternal RSV vaccination compared with placebo reduces infant hospitalisation with laboratory-confirmed RSV disease (risk ratio (RR) 0.50, 95% confidence interval (CI) 0.31 to 0.82; 4 RCTs, 12,216 infants; high-certainty evidence). Based on an absolute risk with placebo of 22 hospitalisations per 1000 infants, our results represent 11 fewer hospitalisations per 1000 infants from vaccinated pregnant women (15 fewer to 4 fewer). No studies reported infant hospitalisation with clinically confirmed RSV disease. Maternal RSV vaccination compared with placebo has little or no effect on the risk of congenital abnormalities (RR 0.96, 95% CI 0.88 to 1.04; 140 per 1000 with placebo, 5 fewer per 1000 with RSV vaccination (17 fewer to 6 more); 4 RCTs, 12,304 infants; high-certainty evidence). Maternal RSV vaccination likely has little or no effect on the risk of intrauterine growth restriction (RR 1.32, 95% CI 0.75 to 2.33; 3 per 1000 with placebo, 1 more per 1000 with RSV vaccination (1 fewer to 4 more); 4 RCTs, 12,545 pregnant women; moderate-certainty evidence). Maternal RSV vaccination may have little or no effect on the risk of stillbirth (RR 0.81, 95% CI 0.38 to 1.72; 3 per 1000 with placebo, no difference with RSV vaccination (2 fewer to 3 more); 5 RCTs, 12,652 pregnant women). There may be a safety signal warranting further investigation related to preterm birth. This outcome may be more likely with maternal RSV vaccination, although the 95% CI includes no effect, and the evidence is very uncertain (RR 1.16, 95% CI 0.99 to 1.36; 6 RCTs, 17,560 infants; very low-certainty evidence). Based on an absolute risk of 51 preterm births per 1000 infants from pregnant women who received placebo, there may be 8 more per 1000 infants from pregnant women with RSV vaccination (1 fewer to 18 more). There was one maternal death in the RSV vaccination group and none in the placebo group. Our meta-analysis suggests that RSV vaccination compared with placebo may have little or no effect on the risk of maternal death (RR 3.00, 95% CI 0.12 to 73.50; 3 RCTs, 7977 pregnant women; low-certainty evidence). The effect of maternal RSV vaccination on the risk of infant death is very uncertain (RR 0.81, 95% CI 0.36 to 1.81; 6 RCTs, 17,589 infants; very low-certainty evidence). AUTHORS' CONCLUSIONS: The findings of this review suggest that maternal RSV vaccination reduces laboratory-confirmed RSV hospitalisations in infants. There are no safety concerns about intrauterine growth restriction and congenital abnormalities. We must be careful in drawing conclusions about other safety outcomes owing to the low and very low certainty of the evidence. The evidence available to date suggests RSV vaccination may have little or no effect on stillbirth, maternal death, and infant death (although the evidence for infant death is very uncertain). However, there may be a safety signal warranting further investigation related to preterm birth. This is driven by data from one trial, which is not fully published yet. The evidence base would be much improved by more RCTs with substantial sample sizes and well-designed observational studies with long-term follow-up for assessment of safety outcomes. Future studies should aim to use standard outcome measures, collect data on concomitant vaccines, and stratify data by timing of vaccination, gestational age at birth, race, and geographical setting.

Exploring parental perspectives: Maternal RSV vaccination versus infant RSV monoclonal antibody.

Respiratory Syncytial Virus poses a significant global public health threat, particularly affecting infants aged less than one year of age. Recently, two forms of passive immunization against infant RSV have been developed and brought to market; nirsevimab a long-acting monoclonal antibody (mAb) and RSV-PreF, a maternal RSV vaccine. The acceptability and uptake of these products will play a pivotal role in determining the success of any national immunization strategy aimed at safeguarding infants from RSV. It is crucial at this time to reflect on the factors that influence parental decisions surrounding immunization to facilitate more informed discussions, enhance healthcare communication, and contribute to the design of effective RSV prevention strategies that resonate with the concerns and aspirations of parents worldwide.

Exacerbated lung inflammation in offspring with high maternal antibody levels following secondary RSV exposure.

Respiratory syncytial virus (RSV) is the primary cause of bronchiolitis-related hospitalizations among children under 5 years of age, with reinfection being common throughout life. Maternal vaccination has emerged as a promising strategy, delivering elevated antibody levels to newborns for immediate protection. However, limited research has explored the protective efficacy of maternal antibodies (matAbs) against secondary RSV infections in offspring. To address this gap, we employed a mouse model of maternal RSV vaccination and secondary infection of offspring to evaluate lung pathology following RSV reinfection in mice with varying levels of maternal antibody (matAb). Additionally, we aimed to investigate the potential causes of exacerbated lung inflammation in offspring with high matAb levels following secondary RSV exposure. Our findings revealed that offspring with elevated levels of maternal pre-F antibody demonstrated effective protection against lung pathology following the initial RSV infection. However, this protection was compromised upon reinfection, manifesting as heightened weight loss, exacerbated lung pathology, increased expression of RSV-A N genes, eosinophilia, enhanced IL-5, IL-13, MUC5AC, and eosinophils Major Basic Protein (MBP) production in lung tissue compared to offspring lacking matAbs. Importantly, these unexpected outcomes were not attributed to antibody-dependent enhancement (ADE) resulting from declining matAb levels over time. Notably, our findings showed a decline in secretory IgA (sIgA), mucosal IgA, and mucosal IgG levels in offspring with high matAb levels post-primary RSV challenge. We propose that this decline may be a critical factor contributing to the ineffective protection observed during secondary RSV exposure. Overall, these findings offer valuable insights into maternal vaccination against RSV, contributing to a comprehensive understanding and mitigation of potential risks associated with maternal RSV vaccination.

XI Reunión Ad Hoc del Grupo Técnico Asesor (GTA) sobre Enfermedades Prevenibles por Vacunación. 21 de noviembre del 2023. Reunión virtual

La Región de las Américas está recuperando sus tasas de cobertura de inmunización para la mayoría de los antígenos. En el 2022, la tasa de cobertura de la tercera dosis de la vacuna contra la difteria, el tétanos y la tos ferina (DTP3) fue del 90%, frente al 86% en 2021. En total, 1,3 millones de niños menores de 1 año siguen sin vacunar, frente a los 1,9 millones de 2021. Por supuesto, el camino hacia la recuperación de la pandemia de COVID-19 es largo, pero las Américas están mostrando signos de progreso. En 2002, los casos de dengue superaron el millón, mientras que en 2013 se registraron más de 2 millones, y más de 3 millones en 2019. Aunque la tasa regional de letalidad por dengue se mantiene por debajo del 0,05%, el aumento de la transmisión está socavando los esfuerzos de recuperación social y económica de los países. En septiembre de 2023, el Grupo de Expertos en Asesoramiento Estratégico (SAGE) sobre Inmunización de la Organización Mundial de la Salud (OMS) recomendó el uso de la serie de dos dosis de la vacuna contra el dengue TAK-003 producida por Takeda para niños de 6 a 16 años que viven en entornos con alta carga de enfermedad por dengue y alta intensidad de transmisión. Durante esta XI reunión del Grupo Técnico Asesor (GTA), la Secretaría de la Organización Panamericana de la Salud (OPS) pidió a los miembros del GTA que consideraran la evidencia sobre la seguridad y eficacia de esta vacuna y propusieran recomendaciones para su uso en las Américas. Asimismo, el virus sincitial respiratorio (VSR) es motivo de gran preocupación en las Américas. Los datos notificados por los Estados Miembros a la red integrada de vigilancia respiratoria SARInet Plus de la OPS indican que el VSR contribuye significativamente a la carga de enfermedades respiratorias en la Región. Por grupos de edad, los casos y hospitalizaciones asociados al VSR se han notificado principalmente entre lactantes menores de 2 años. En los últimos meses, tanto la Administración de Alimentos y Medicamentos de EE.UU. (FDA) como la Agencia Europea del Medicamento (EMA) han aprobado la vacuna Abrysvo contra el VRSpreF producida por Pfizer para mujeres embarazadas, con el objetivo de reducir la incidencia del VRS entre los recién nacidos menores de 6 meses. Una vez más, los miembros del GAT fueron convocados para proporcionar sus recomendaciones a la OPS sobre el uso de esta vacuna en las Américas.

Mutations in the F protein of the live-attenuated respiratory syncytial virus vaccine candidate ΔNS2/Δ1313/I1314L increase the stability of infectivity and content of prefusion F protein.

Respiratory syncytial virus (RSV) is the leading viral cause of bronchiolitis and pneumonia in infants and toddlers, but there currently is no licensed pediatric vaccine. A leading vaccine candidate that has been evaluated for intranasal immunization in a recently completed phase 1/2 clinical trial is an attenuated version of RSV strain A2 called RSV/ΔNS2/Δ1313/I1314L (hereafter called ΔNS2). ΔNS2 is attenuated by deletion of the interferon antagonist NS2 gene and introduction into the L polymerase protein gene of a codon deletion (Δ1313) that confers temperature-sensitivity and is stabilized by a missense mutation (I1314L). Previously, introduction of four amino acid changes derived from a second RSV strain "line 19" (I79M, K191R, T357K, N371Y) into the F protein of strain A2 increased the stability of infectivity and the proportion of F protein in the highly immunogenic pre-fusion (pre-F) conformation. In the present study, these four "line 19" assignments were introduced into the ΔNS2 candidate, creating ΔNS2-L19F-4M. During in vitro growth in Vero cells, ΔNS2-L19F-4M had growth kinetics and peak titer similar to the ΔNS2 parent. ΔNS2-L19F-4M exhibited an enhanced proportion of pre-F protein, with a ratio of pre-F/total F that was 4.5- to 5.0-fold higher than that of the ΔNS2 parent. The stability of infectivity during incubation at 4°C, 25°C, 32°C and 37°C was greater for ΔNS2-L19F-4M; for example, after 28 days at 32°C, its titer was 100-fold greater than ΔNS2. ΔNS2-L19F-4M exhibited similar levels of replication in human airway epithelial (HAE) cells as ΔNS2. The four "line 19" F mutations were genetically stable during 10 rounds of serial passage in Vero cells. In African green monkeys, ΔNS2-L19F-4M and ΔNS2 had similar growth kinetics, peak titer, and immunogenicity. These results suggest that ΔNS2-L19F-4M is an improved live attenuated vaccine candidate whose enhanced stability may simplify its manufacture, storage and distribution, which merits further evaluation in a clinical trial in humans.

Monoclonal antibodies targeting sites in respiratory syncytial virus attachment G protein provide protection against RSV-A and RSV-B in mice.

Currently, only Palivizumab and Nirsevimab that target the respiratory syncytical virus (RSV) fusion protein are licensed for pre-treatment of infants. Glycoprotein-targeting antibodies may also provide protection against RSV. In this study, we generate monoclonal antibodies from mice immunized with G proteins from RSV-A2 and RSV-B1 strains. These monoclonal antibodies recognize six unique antigenic classes (G0-G5). None of the anti-G monoclonal antibodies neutralize RSV-A2 or RSV-B1 in vitro. In mice challenged with either RSV-A2 line 19 F or RSV-B1, one day after treatment with anti-G monoclonal antibodies, all monoclonal antibodies reduce lung pathology and significantly reduce lung infectious viral titers by more than 2 logs on day 5 post-RSV challenge. RSV dissemination in the lungs was variable and correlated with lung pathology. We demonstrate new cross-protective anti-G monoclonal antibodies targeting multiple sites including conformation-dependent class G0 MAb 77D2, CCD-specific class G1 MAb 40D8, and carboxy terminus of CCD class G5 MAb 7H11, to support development of G-targeting monoclonal antibodies against RSV.

Mucosal immunization with a low-energy electron inactivated respiratory syncytial virus vaccine protects mice without Th2 immune bias.

The respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory tract infections associated with numerous hospitalizations. Recently, intramuscular (i.m.) vaccines against RSV have been approved for elderly and pregnant women. Noninvasive mucosal vaccination, e.g., by inhalation, offers an alternative against respiratory pathogens like RSV. Effective mucosal vaccines induce local immune responses, potentially resulting in the efficient and fast elimination of respiratory viruses after natural infection. To investigate this immune response to an RSV challenge, low-energy electron inactivated RSV (LEEI-RSV) was formulated with phosphatidylcholine-liposomes (PC-LEEI-RSV) or 1,2-dioleoyl-3-trimethylammonium-propane and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DD-LEEI-RSV) for vaccination of mice intranasally. As controls, LEEI-RSV and formalin-inactivated-RSV (FI-RSV) were used via i.m. vaccination. The RSV-specific immunogenicity of the different vaccines and their protective efficacy were analyzed. RSV-specific IgA antibodies and a statistically significant reduction in viral load upon challenge were detected in mucosal DD-LEEI-RSV-vaccinated animals. Alhydrogel-adjuvanted LEEI-RSV i.m. showed a Th2-bias with enhanced IgE, eosinophils, and lung histopathology comparable to FI-RSV. These effects were absent when applying the mucosal vaccines highlighting the potential of DD-LEEI-RSV as an RSV vaccine candidate and the improved performance of this mucosal vaccine candidate.

Maternal awareness, acceptability and willingness towards respiratory syncytial virus (RSV) vaccination during pregnancy in Ireland.

BACKGROUND: Respiratory syncytial virus (RSV) is the world's leading cause of viral acute lower respiratory infections (ALRI) in infants. WHO has identified maternal RSV vaccination a priority and candidate vaccines are in development; however, vaccine hesitancy remains an impediment to successful implementation of maternal immunization. This study, the largest antenatal survey conducted to-date, aimed to examine maternal RSV awareness, likely acceptance of RSV vaccination in pregnancy, and attitudes to maternal vaccination. METHODS: Pregnant women of all gestations attending antenatal clinic of a university maternity hospital in Ireland were invited to participate. An information leaflet provided, consent obtained, and survey administered examining RSV awareness, willingness to avail of antenatal RSV vaccination, factors influencing acceptability and preferred sources of assistance. Research Ethics Committee (REC) approval obtained, and general data protection regulation (GDPR) guidelines followed. RESULTS: 528 women completed the survey. A large proportion (75.6%) had never heard of RSV, yet 48.5% would still avail of a vaccine, 45.8% were undecided and only 5.3% would not. The main factor making vaccination acceptable to women (76.4%) was that it protects their infant from illness (p < .001, CV 0.336 for association with acceptance) and general practitioner (GP) was the preferred guidance source in decision-making (57.7%). CONCLUSIONS: Despite low levels of maternal awareness of RSV, pregnant women in Ireland are open to availing of antenatal vaccination. Maternal immunization strategies need to focus on infant's protection from RSV-associated ALRI along with vaccine safety, and build on an interdisciplinary collaboration of maternal, neonatal, primary care and public health services.

From Forgotten Pathogen to Target for New Vaccines: What Clinicians Need to Know about Respiratory Syncytial Virus Infection in Older Adults.

Respiratory syncytial virus (RSV) is increasingly recognized as being implicated in acute illness in older adults, with a significant weight in hospitalizations for respiratory illness and death. By means of a best-evidence review, this paper aims to investigate whether RSV can be considered a forgotten pathogen in older patients, looking at trends in the literature volume and exploring possible epidemiological and clinical features underlying the focus given to it. We then present an assessment of its disease burden and present and future strategies for its reduction, particularly in light of the recent availability of new vaccines.

Development of innate and adaptive immunity to RSV in young children.

Infection of the respiratory tract with respiratory syncytial virus (RSV) is common and occurs repeatedly throughout life with most severe disease occurring at the extremes of age: in young infants and the elderly. Effective anti-viral therapeutics are not available and therefore prevention has been the primary strategy for reducing the disease burden. Our current understanding of respiratory mucosal cell biology and the immune response within the respiratory tract is inadequate to prevent infection caused by a pathogen like RSV that does not disseminate outside of this environment. Gaps in our understanding of the activation of innate and adaptive immunity in response to RSV and the role of age upon infection also limit improvements in the design of therapeutics and vaccines for young infants. However, advancements in structural biology have improved our ability to characterize antibodies against viral proteins and in 2023 the first vaccines for those over 60 years and pregnant women became available, potentially reducing the burden of disease. This review will examine our current understanding of the critical facets of anti-RSV immune responses in infants and young children as well as highlight areas where more research is needed.

VLPs generated by the fusion of RSV-F or hMPV-F glycoprotein to HIV-Gag show improved immunogenicity and neutralizing response in mice.

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) vaccines have been long overdue. Structure-based vaccine design created a new momentum in the last decade, and the first RSV vaccines have finally been approved in older adults and pregnant individuals. These vaccines are based on recombinant stabilized pre-fusion F glycoproteins administered as soluble proteins. Multimeric antigenic display could markedly improve immunogenicity and should be evaluated in the next generations of vaccines. Here we tested a new virus like particles-based vaccine platform which utilizes the direct fusion of an immunogen of interest to the structural human immunodeficient virus (HIV) protein Gag to increase its surface density and immunogenicity. We compared, in mice, the immunogenicity of RSV-F or hMPV-F based immunogens delivered either as soluble proteins or displayed on the surface of our VLPs. VLP associated F-proteins showed better immunogenicity and induced superior neutralizing responses. Moreover, when combining both VLP associated and soluble immunogens in a heterologous regimen, VLP-associated immunogens provided added benefits when administered as the prime immunization.

RSV Vaccination Intention Among People Who Are or Plan to Become Pregnant.

OBJECTIVES: Respiratory syncytial virus (RSV) is a common pediatric infection, with young infants being at the highest risk of hospitalization and long-term sequela. New preventive agents have been recommended to prevent severe RSV illness in infants, including a vaccine administered during pregnancy. The current rates of recommended vaccination in pregnancy are suboptimal. Our objective was to characterize interest in RSV vaccination during pregnancy among people across the United States who were pregnant or planning to become pregnant. METHODS: In March 2023, we conducted a national cross-sectional online survey of individuals 18 to 45 years old who were currently pregnant or trying to become pregnant on their perceptions of RSV-related illness and intentions to get vaccinated against RSV. We performed logistic regression analyses to determine the odds and predicted proportions of the likelihood of RSV vaccination during pregnancy, controlling for sociodemographic factors. RESULTS: Of 1619 completed surveys, 1528 were analyzed. 54% of respondents indicated that they were "very likely" to get vaccinated against RSV during pregnancy. The perception of RSV as a serious illness was the strongest predictor of vaccination likelihood. In the full regression model, predicted proportions of "very likely" to vaccinate against RSV followed a similar pattern (63% if RSV infection was perceived as serious and likely, 55% if serious and unlikely, 35% if not serious; P < .001). CONCLUSIONS: Raising awareness of RSV infection as likely and potentially serious for infants may be an influential component of targeted communications that promote RSV vaccine uptake during pregnancy.

Equivalent immunogenicity across three RSVpreF vaccine lots in healthy adults 18-49 years of age: Results of a randomized phase 3 study.

BACKGROUND: Bivalent RSV prefusion F subunit vaccine (RSVpreF), comprised of equal quantities of stabilized prefusion F antigens from the major circulating subgroups (RSV A, RSV B), is licensed for prevention of RSV-associated lower respiratory tract illness (LRTI) in older adults and for maternal vaccination for prevention of RSV-associated LRTI in infants. To support licensure and large-scale manufacturing, this lot consistency study was conducted to demonstrate equivalence in immunogenicity across 3 RSVpreF lots. METHODS: This phase 3, multicenter, parallel-group, placebo-controlled, randomized (1:1:1:1), double-blind study evaluated immunogenicity, safety, and tolerability of RSVpreF in healthy 18-49-year-old adults. Participants received a single 120-µg injection of 1 of 3RSVpreF lots or placebo. Geometric mean ratio (GMR) of RSV serum 50 % neutralizing geometric mean titers obtained 1 month after vaccination were compared between each vaccine lot for RSV A and RSV B, separately. Equivalence between lots was defined using a 1.5-fold criterion (GMR 95 % CIs for every lot pair within the 0.667-1.5 interval). Safety and tolerability were assessed. RESULTS: Of 992participants vaccinated, 948 were included in the evaluable immunogenicity population. All 3 RSVpreF lots elicited strong immune responses, meeting the 1.5-fold equivalence criterion for all between-lot comparisons for both RSV A and RSV B. Across the 3 lots, RSV A and RSV B 50 % neutralizing geometric mean titers substantially increased from baseline (RSV A, 1671-1795; RSV B 1358-1429) to 1 month after RSVpreF vaccination (RSV A, 24,131-25,238; RSV B, 19,238-21,702), corresponding to ≥14-fold increases in 50 % neutralizing titers for both RSV A and RSV B from before to 1 month after vaccination. Single doses of RSVpreF were safe and well tolerated, with similar safety profiles across the 3 RSVpreF lots. CONCLUSIONS: These findings support the reproducibility of RSVpreF vaccine manufacturing with similar safety and reactogenicity profiles (NCT05096208).

Engineered dityrosine-bonding of the RSV prefusion F protein imparts stability and potency advantages.

Viral fusion proteins facilitate cellular infection by fusing viral and cellular membranes, which involves dramatic transitions from their pre- to postfusion conformations. These proteins are among the most protective viral immunogens, but they are metastable which often makes them intractable as subunit vaccine targets. Adapting a natural enzymatic reaction, we harness the structural rigidity that targeted dityrosine crosslinks impart to covalently stabilize fusion proteins in their native conformations. We show that the prefusion conformation of respiratory syncytial virus fusion protein can be stabilized with two engineered dityrosine crosslinks (DT-preF), markedly improving its stability and shelf-life. Furthermore, it has 11X greater potency as compared with the DS-Cav1 stabilized prefusion F protein in immunogenicity studies and overcomes immunosenescence in mice with simply a high-dose formulation on alum.