Vaccino in gravidanza per prevenire la bronchiolite da VRS nei lattanti: i risultati di un RCT di fase 3

Abstract

Vaccine in pregnancy to prevent VRS bronchiolitis in infants: results of a phase 3 RCT Sponsored by Pfizer, this multicenter, double-blind phase 3 RCT conducted in 18 countries from 2020 to 2022 in 4 seasons (two in the Northern Hemisphere and two in the Southern Hemisphere) tested the efficacy of the bivalent RSVpreF vaccine in pregnant women (3.682 intervention group, 3.676 control group) on the prevention of respiratory syncytial virus (VRS)-associated lower respiratory tract infections in their offspring by 180 days of age. Hospitalizations were not considered as the primary endpoint but VRS infections in general and, distinctly, severe VRS infections. Severe lower respiratory tract VRS infections occurred within 90 days in 6 children of vaccinated mothers and in 33 children of mothers who received placebo (vaccine efficacy 81.8%; 99.5%IC 40.6-96.3; statistically significant), within 180 days in 19 children of vaccinated mothers and in 62 children of mothers who received placebo (vaccine efficacy 69.4%; 97.58%IC 44.3-84.1). Lower respiratory tract VRS infections occurred within 90 days in 24 offspring of vaccinated mothers and in 56 offspring of mothers who received placebo (vaccine efficacy 57.1%; 99.5%IC 14.7-79.8 not statistically significant), within 180 days in 57 offspring of vaccinated mothers and in 117 offspring of mothers who received placebo (vaccine efficacy 51.3%; 97.58% CI, 29.4 to 66.8). The incidence of severe adverse effects in children up to 2 years old was similar in the two groups. 201 children (5.6%) were born prematurely to vaccinated mothers versus 169 children (4.7%) in the placebo group; the difference was not statistically significant. A vaccine very similar to the one under study produced by GSK was withdrawn in February 2022 due to an increased risk of preterm birth in the vaccine arm. Since both preterm births and low birth weight were considered secondary safety endpoints and not primary safety endpoints doubts remain with respect to the safety of the RSVpreF vaccine, and several scholars have asked Pfizer to investigate this further.