• SimõesEric A FEAFFrom the University of Colorado School of Medicine and Children's Hospital Colorado, Aurora (E.A.F.S.); Vaccine Research and Development, Pfizer, Pearl River, NY (K.J.C., K.A.S., D.R., S.B.M., E.G., D.A.S., K.U.J., W.C.G., P.R.D., A.C.G.), Kimberly J Center, TitaAlan T NATNFrom the University of Colorado School of Medicine and Children's Hospital Colorado, Aurora (E.A.F.S.); Vaccine Research and Development, Pfizer, Pearl River, NY (K.J.C., K.A.S., D.R., S.B.M., E.G., D.A.S., K.U.J., W.C.G., P.R.D., A.C.G.); , Kena A Swanson, David Radley, John Houghton, Stephanie B McGrory, Emily Gomme, Marquita Anderson, John P Roberts, Daniel A Scott, Kathrin U Jansen, William C Gruber, Philip R Dormitzer, and Alejandra C Gurtman.
• From the University of Colorado School of Medicine and Children's Hospital Colorado, Aurora (E.A.F.S.); Vaccine Research and Development, Pfizer, Pearl River, NY (K.J.C., K.A.S., D.R., S.B.M., E.G., D.A.S., K.U.J., W.C.G., P.R.D., A.C.G.); the Center for Women's Reproductive Health and the Department of Obstetrics and Gynecology, University of Alabama, Birmingham (A.T.N.T.); the Iowa Clinic, Des Moines (J.H.); and Gadolin Research, Beaumont (M.A.), and Ventavia Research Group, Plano (J.P.R.) - both in Texas.
• N. Engl. J. Med. 2022 Apr 28; 386 (17): 1615-1626.

BackgroundRespiratory syncytial virus (RSV), a major cause of illness and death in infants worldwide, could be prevented by vaccination during pregnancy. The efficacy, immunogenicity, and safety of a bivalent RSV prefusion F protein-based (RSVpreF) vaccine in pregnant women and their infants are uncertain.MethodsIn a phase 2b trial, we randomly assigned pregnant women, at 24 through 36 weeks' gestation, to receive either 120 or 240 μg of RSVpreF vaccine (with or without aluminum hydroxide) or placebo. The trial included safety end points and immunogenicity end points that, in this interim analysis, included 50% titers of RSV A, B, and combined A/B neutralizing antibodies in maternal serum at delivery and in umbilical-cord blood, as well as maternal-to-infant transplacental transfer ratios.ResultsThis planned interim analysis included 406 women and 403 infants; 327 women (80.5%) received RSVpreF vaccine. Most postvaccination reactions were mild to moderate; the incidence of local reactions was higher among women who received RSVpreF vaccine containing aluminum hydroxide than among those who received RSVpreF vaccine without aluminum hydroxide. The incidences of adverse events in the women and infants were similar in the vaccine and placebo groups; the type and frequency of these events were consistent with the background incidences among pregnant women and infants. The geometric mean ratios of 50% neutralizing titers between the infants of vaccine recipients and those of placebo recipients ranged from 9.7 to 11.7 among those with RSV A neutralizing antibodies and from 13.6 to 16.8 among those with RSV B neutralizing antibodies. Transplacental neutralizing antibody transfer ratios ranged from 1.41 to 2.10 and were higher with nonaluminum formulations than with aluminum formulations. Across the range of assessed gestational ages, infants of women who were immunized had similar titers in umbilical-cord blood and similar transplacental transfer ratios.ConclusionsRSVpreF vaccine elicited neutralizing antibody responses with efficient transplacental transfer and without evident safety concerns. (Funded by Pfizer; ClinicalTrials.gov number, NCT04032093.).Copyright © 2022 Massachusetts Medical Society.

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