Clinical Question

Does maternal respiratory syncytial virus (RSV) vaccination safely reduce the likelihood of RSV in their newborns?

Bottom Line

A bivalent RSV vaccine given to pregnant women between 24 and 36 weeks’ gestation safely reduces the likelihood of severe RSV in their newborns (number needed to treat [NNT] = 81 at six months of age). (Level of Evidence = 1b−)

Synopsis

The Pfizer-sponsored study evaluated a new RSV vaccine (RSVpreF 60 mcg RSV A and 60 mcg RSV B) in pregnant women. The participating women were healthy, and they received the immunization or placebo injection between 24 and 36 weeks’ gestation. A total of 7,392 pregnant women were enrolled; 7,148 of them gave birth. At baseline, mean age was 29 years; mean gestational age was 31 weeks; and 20% were Black, 12.5% were Asian, and 29% were Hispanic. Groups were balanced, but it was not reported whether analysis was per protocol or intention to treat. This is important because retention in the trial was only fair, with approximately 80% still enrolled at six months. Because it was an interim analysis, this may improve in the final analysis. At six months after birth, the likelihood of a medically attended, severe RSV-associated lower respiratory tract illness was significantly lower in the vaccine group (0.5% vs. 1.8%; P < .05; NNT = 81). The likelihood of any medically attended RSV lower respiratory tract illness was also lower in the vaccine group at six months (1.6% vs. 3.4%; P < .05; NNT = 58). Vaccine efficacy was estimated to be 67% for the outcome of RSV hospitalization. Local reactions occurred in 41% of the vaccine group compared with 10% in the placebo group. Muscle pain was more common in the vaccine group (27% vs. 17%). There were no differences in broader maternal or neonatal outcomes, with five infant deaths in the vaccine group and 12 in the placebo group during follow-up.