A bivalent respiratory syncytial virus (RSV) prefusion F protein-based (RSVpreF) vaccine given during pregnancy elicits neutralizing antibody responses, according to a study published in the New England Journal of Medicine. Eric A.F. Simões, MD, and colleagues randomly assigned pregnant women at 24-36 weeks of gestation to receive 120 or 240 μg of RSVpreF vaccine (with or without aluminum hydroxide) or placebo in a phase IIb trial. A total of 406 women and 403 infants were included in the planned interim analysis; 80.5% of women received RSVpreF vaccine. Most postvaccination reactions were mild to moderate; women who received RSVpreF vaccine containing aluminum hydroxide had a higher incidence of local reactions than those who received RSVpreF vaccine without aluminum hydroxide. For women and infants, the incidences of adverse events were similar in the vaccine and placebo groups; the type and frequency of events were consistent with background incidences.