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RSV vaccines

Author Prof E. Harms, Münster University Children’s Hospital (Germany)

RSV infections are among the most common reasons for hospitalisation in the first year of life. A double-blind, placebo-controlled, randomised phase 3 trial conducted in 18 countries examined whether vaccinating pregnant women at 24 through 36 weeks’ gestation with a bivalent RSV prefusion F protein-based (RSVpreF) vaccine prevents their children from developing a severe RSV-associated lower respiratory tract illness during the first six months of life [1].
The study population was randomised with an allocation ratio of 1:1, whereby 3682 pregnant women received the vaccine. All RSV-associated lower respiratory tract illness of both groups (vaccine and placebo group) were recorded. The overall vaccine efficacy was 57% after 90 days and 51% after 180 days; vaccine efficacy against severe cases (hospitalisation, some in intensive care) was 82% after 90 days and 69% after 180 days.

Comment: This study is a milestone in the battle against RSV infections in newborns and infants. The previous practice of protecting infants who are at risk (for example, due to preterm delivery or previous neonatal intensive care) by administering specific antibodies has not always been successful and has only reached a fraction of at-risk infants. Actively vaccinating infants in their early stages does not necessarily lead to a positive outcome. Therefore, this study took a clever route by vaccinating mothers closer to their due dates, allowing them to pass on protective antibodies through the placenta – similar to what we know from other infectious diseases. It’s expected that this method won’t provide complete protection and that efficacy diminishes over time, as seen in the 90-day and 180-day results. However, this does not diminish the value of the maternal vaccination strategy.

[1] Kampmann B, Madhi SA, Munjal I et al. Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants. N Engl J Med 2023; 388: 1451–64.DOI: 10.1056/NEJMoa2216480.