Evaluation of the effectiveness of the respiratory syncytial virus vaccine in children under 6 months of age in Córdoba, Argentina.

ntroduction. The recently approved vaccine against respiratory syncytial virus (RSV) is administered to pregnant women and confers immunity to their babies; however, the evaluation of its effectiveness is limited. Objective. To evaluate the effectiveness of the vaccine against hospitalization due to RSV in children under 6 months of age during the vaccination campaign for pregnant women. Population and methods. Case-control study nested in a cohort of newborns whose mothers were indicated for RSV vaccination in Córdoba, Argentina. We included 180 cases with positive laboratory results for RSV and 1,069 asymptomatic controls who attended routine check-ups. Multiple logistic regression models were performed considering the presence of RSV as the primary response variable, adjusted for maternal age, gestational age, birth weight, maternal influenza vaccination, maternal education level, and multiple births. Vaccine effectiveness was calculated using the formula EV = (1 - OR) × 100. Results. The RSV vaccine reduces the likelihood of becoming ill with RSV by 74.0% (OR: 0.26; CI: 0.170.39); the influenza vaccine reduces it by 70% (OR: 0.30; CI: 0.21-0.43). For each completed week of gestational age, protection against the disease increases by 10% (OR: 0.90; CI: 0.81-0.99). Conclusion. The vaccine is effective against hospitalization due to RSV in children under 6 months of age, who are the most vulnerable population, and could be an essential tool for reducing morbidity and mortality due to RSV.