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BACKGROUNDWhether vaccination during pregnancy could reduce the burden of respiratory syncytial virus (RSV)-associated lower respiratory tract illness in newborns and infants is uncertain. METHODSIn this phase 3, double-blind trial conducted in 18 countries, we randomly assigned, in a 1:1 ratio, pregnant women at 24 through 36 weeks' gestation to receive a single intramuscular injection of 120 μg of a bivalent RSV prefusion F proteinbased (RSVpreF) vaccine or placebo. The two primary efficacy end points were medically attended severe RSV-associated lower respiratory tract illness and medically attended RSV-associated lower respiratory tract illness in infants within 90, 120, 150, and 180 days after birth. A lower boundary of the confidence interval for vaccine efficacy (99.5% confidence interval [CI] at 90 days; 97.58% CI at later intervals) greater than 20% was considered to meet the success criterion for vaccine efficacy with respect to the primary end points. RESULTSAt this prespecified interim analysis, the success criterion for vaccine efficacy was met with respect to one primary end point. Overall, 3682 maternal participants received vaccine and 3676 received placebo; 3570 and 3558 infants, respectively, were evaluated. Medically attended severe lower respiratory tract illness occurred within 90 days after birth in 6 infants of women in the vaccine group and 33 infants of women in the placebo group (vaccine efficacy, 81.8%; 99.5% CI, 40.6 to 96.3); 19 cases and 62 cases, respectively, occurred within 180 days after birth (vaccine efficacy, 69.4%; 97.58% CI, 44.3 to 84.1). Medically attended RSV-associated lower respiratory tract illness occurred within 90 days after birth in 24 infants of women in the vaccine group and 56 infants of women in the placebo group (vaccine efficacy, 57.1%; 99.5% CI, 14.7 to 79.8); these results did not meet the statistical success criterion. No safety signals were detected in maternal participants or in infants and toddlers up to 24 months of age. The incidences of adverse events reported within 1 month after injection or within 1 month after birth were similar in the vaccine group (13.8% of women and 37.1% of infants) and the placebo group (13.1% and 34.5%, respectively). CONCLUSIONSRSVpreF vaccine administered during pregnancy was effective against medically attended severe RSV-associated lower respiratory tract illness in infants, and no safety concerns were identified. (Funded by Pfizer; MATISSE ClinicalTrials.gov number, NCT04424316.

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Background Interventions to tackle the COVID-19 pandemic may affect the burden of other respiratory diseases. Considering the repercussion of these unique social experiences in infant’s health, this study aims to assess the early impact of social distancing due to the COVID-19 pandemic in hospital admissions for acute bronchiolitis. Methods Data from hospitalizations of acute bronchiolitis in infants under one year were obtained from the Department of Informatics of the Brazilian Public Health database (DATASUS) for the period between 2016 and 2020. These data were also analyzed by macro-regions of Brazil (North, Northeast, Southeast, South and Midwest). To evaluate the effect of social distancing strategy on the incidence of acute bronchiolitis, the absolute and relative reduction was calculated by analyzing the yearly subsets of 2016vs2020, 2017vs2020, 2018vs2020, and 2019vs2020. Results There was a significant reduction in all comparisons, ranging from -78% [IRR 0.22 (0.20 to 0.24)] in 2016vs2020 at -85% [IRR 0.15 (0.13 to 0.16)] in 2019vs2020, for the data from Brazil. For analyzes by macro-regions, the reduction varied from -58% [IRR 0.41 (0.37 to 0.45)] in the Midwest in 2016vs2020 to -93% [IRR 0.07 (0.06 to 0.08)] in the South in 2019vs2020. Conclusions There was a significant reduction in hospitalization for acute bronchiolitis in children under one year old, in Brazil, of the order of more than 70% for most analysis. Our data suggest an important impact of social distance on reducing the transmission of viruses related to acute bronchiolitis. Such knowledge may guide strategies for prevention of viruses spread.