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In a phase 3 trial, adults (≥60 years of age) received one 120-μg dose of RSVpreF vaccine (17,215) or placebo (17,069). Vaccine efficacy against RSV-associated lower respiratory tract illness was 67 to 86%.

Whether vaccination during pregnancy could reduce the burden of respiratory syncytial virus (RSV)-associated lower respiratory tract illness in newborns and infants is uncertain. In this phase 3, double-blind trial conducted in 18 countries, we randomly assigned, in a 1:1 ratio, pregnant women at 24 through 36 weeks' gestation to receive a single intramuscular injection of 120 μg of a bivalent RSV prefusion F protein-based (RSVpreF) vaccine or placebo. The two primary efficacy end points were medically attended severe RSV-associated lower respiratory tract illness and medically attended RSV-associated lower respiratory tract illness in infants within 90, 120, 150, and 180 days after birth. A lower boundary of the confidence interval for vaccine efficacy (99.5% confidence interval [CI] at 90 days; 97.58% CI at later intervals) greater than 20% was considered to meet the success criterion for vaccine efficacy with respect to the primary end points. At this prespecified interim analysis, the success criterion for vaccine efficacy was met with respect to one primary end point. Overall, 3682 maternal participants received vaccine and 3676 received placebo; 3570 and 3558 infants, respectively, were evaluated. Medically attended severe lower respiratory tract illness occurred within 90 days after birth in 6 infants of women in the vaccine group and 33 infants of women in the placebo group (vaccine efficacy, 81.8%; 99.5% CI, 40.6 to 96.3); 19 cases and 62 cases, respectively, occurred within 180 days after birth (vaccine efficacy, 69.4%; 97.58% CI, 44.3 to 84.1). Medically attended RSV-associated lower respiratory tract illness occurred within 90 days after birth in 24 infants of women in the vaccine group and 56 infants of women in the placebo group (vaccine efficacy, 57.1%; 99.5% CI, 14.7 to 79.8); these results did not meet the statistical success criterion. No safety signals were detected in maternal participants or in infants and toddlers up to 24 months of age. The incidences of adverse events reported within 1 month after injection or within 1 month after birth were similar in the vaccine group (13.8% of women and 37.1% of infants) and the placebo group (13.1% and 34.5%, respectively). RSVpreF vaccine administered during pregnancy was effective against medically attended severe RSV-associated lower respiratory tract illness in infants, and no safety concerns were identified. (Funded by Pfizer; MATISSE ClinicalTrials.gov number, NCT04424316.).

Respiratory syncytial virus causes clinically significant illness in children and adults. In a placebo-controlled trial, a prefusion stabilized F protein vaccine led to an 83% lower risk of RSV infection.

In a placebo-controlled, phase 2–3 trial, one dose of mRNA-1345 led to a lower incidence of RSV disease among adults 60 years of age or older. Solicited local and systemic adverse reactions occurred more often with the vaccine.

A combination of adenovirus 26 and protein vaccines was used to deliver a prefusion stabilized RSV protein. RSV-related lower respiratory tract illness developed in fewer vaccine recipients than placebo recipients.

Respiratory syncytial virus is a major cause of illness in infants. In this randomized, double-blind, placebo-controlled trial, the safety and immunogenicity of a bivalent RSV prefusion F protein–based vaccine was assessed in pregnant women and their infants. Anti-RSV antibodies were elicited with efficient transplacental transfer.

An RSV prefusion F maternal vaccine was assessed for efficacy against RSV disease in infants. The trial was stopped early owing to a higher incidence of preterm birth in the vaccine group than in the placebo group.

Nirsevimab, a monoclonal antibody with an extended half-life, is designed to protect infants from respiratory syncytial virus disease after a single intramuscular dose. This placebo-controlled trial involving 1447 preterm infants at 164 sites in 23 countries assessed the effectiveness of nirsevimab over 150 days after the dose was administered.

Technologies that define the atomic-level structure of neutralization-sensitive epitopes on viral surface proteins are transforming vaccinology and guiding new vaccine development approaches. Previously, iterative rounds of protein engineering were performed to preserve the prefusion conformation of the respiratory syncytial virus (RSV) fusion (F) glycoprotein, resulting in a stabilized subunit vaccine candidate (DS-Cav1), which showed promising results in mice and macaques. Here, phase I human immunogenicity data reveal a more than 10-fold boost in neutralizing activity in serum from antibodies targeting prefusion-specific surfaces of RSV F. These findings represent a clinical proof of concept for structure-based vaccine design, suggest that development of a successful RSV vaccine will be feasible, and portend an era of precision vaccinology.

Nirsevimab, a monoclonal antibody targeting RSV, led to decreased hospitalizations for RSV-associated lower respiratory tract infection in infants during their first RSV season, in an open-label, pragmatic trial.