Bivalent respiratory syncytial virus (RSV) vaccine given to mothers reduces total and severe RSV infections in infants

Reference

Kampmann B, Madhi SA, Munjal I, et al, for the MATISSE Study Group. Bivalent prefusion F vaccine in pregnancy to prevent RSV illness in infants. N Engl J Med 2023;388(16):1451-1464.

Synopsis

The severe RSV season in 2022 and 2023 put this infection on our radar, especially for infants and the elderly. This Pfizer-sponsored study evaluated a novel 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 7392 pregnant women were enrolled; 7148 of them gave birth. At baseline, their mean age was 29 years; the 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 6 months. As this was an interim analysis, that may improve in the final analysis. At 6 months after birth, the likelihood of medically attended severe RSV lower respiratory tract illness (RTI) was significantly lower in the vaccine group (1.8% vs 0.5%; P < .05; number needed to treat [NNT] = 81). The likelihood of any medically attended RSV lower RTI was also lower in the vaccine group at 6 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 also more common in the vaccine group (27% vs 17%). There were no differences in broader maternal or neonatal outcomes, with 5 infant deaths in the vaccine group and 12 in the placebo group during follow-up.