The specific maternal-neonatal immunity against respiratory syncytial virus after the COVID-19 pandemic: an observational study.

Children in the first months of life are at highest risk for Respiratory Syncytial Virus (RSV) bronchiolitis. Maternal specific anti-RSV IgG antibodies play a key role in preventing infection in early life. The COVID-19 pandemic changed the seasonality of RSV epidemics. We hypothesized that COVID-19 restrictions, affecting RSV circulation, altered RSV-specific immunity of pregnant women and their newborns. We compared anti-RSV IgM and IgG levels in maternal and cord blood (CB) samples collected from mother-newborn dyads at Policlinico Umberto I Hospital, Rome, Italy, across three consecutive RSV seasons: Group 1 (Nov 2020-Mar 2021; N: 24 dyads), Group 2 (Nov 2021-Mar 2022; N: 38 dyads), and Group 3 (Sep 2022-Mar 2023; N: 31 dyads). Median maternal anti-RSV IgM values were significantly higher in Group 3 (p = 0.001) and in Group 2 (p = 0.004) compared to Group 1. Anti-RSV IgG median values were significantly lower in Group 2 both in maternal (p = 0.039) and CB (p = 0.05) and in Group 3 in CB (p = 0.029) compared to Group 1. These findings suggest that the COVID-19 pandemic caused an RSV-specific immunological debit in pregnant women and their infants, potentially explaining the altered RSV seasonality and increased bronchiolitis hospitalizations during 2021-2022.