RSVpreF is being developed to prevent RSV-associated moderate to severe lower respiratory tract disease in adults 60 years of age and in infants by active immunization of pregnant women.

This Phase 2a study is an exploratory proof-of-concept to assess the safety, immunogenicity, and efficacy of RSVpreF using a human challenge model. The RSV challenge model is developed to help understand the RSV disease and assess new vaccines by testing them in participants deliberately infected with the virus.

In this study, approximately 62 (up to 72) participants will be vaccinated with the investigational RSVpreF to account for withdrawals between vaccination and challenge. Participants will be randomized 1:1 to receive RSVpreF or placebo.

Results

The New England Journal of Medicine published the results of this trial on June 23, 2022.

After participants were inoculated with the challenge virus, vaccine efficacy of 86.7% (95% CI, 53.8 to 96.5) was observed for symptomatic RSV infection confirmed by any detectable viral RNA on at least 2 consecutive days.

The median AUC for the RSV viral load (hours×log10 copies per milliliter) as measured by RT-qPCR assay was 0.0 (interquartile range, 0.0 to 19.0) in the vaccine group and 96.7 (interquartile range, 0.0 to 675.3) in the placebo group. The geometric mean factor increase from baseline in RSV A–neutralizing titers 28 days after injection was 20.5 (95% CI, 16.6 to 25.3) in the vaccine group and 1.1 (95% CI, 0.9 to 1.3) in the placebo group. More local injection-site pain was noted in the vaccine group than in the placebo group. No serious adverse events were observed in either group.

Conclusion

RSVpreF vaccine was effective against symptomatic RSV infection and viral shedding. No evident safety concerns were identified. These findings provide support for further evaluation of the RSVpreF vaccine in a phase 3 efficacy study.