Impact of previous SARS-CoV-2 infection on the severity of respiratory syncytial virus infection in hospitalized children.

Respiratory syncytial virus (RSV) is a major cause of hospitalization in young children, but the impact of previous SARS-CoV-2 infection on RSV disease severity remains unclear. This study assessed whether prior or recent SARS-CoV-2 infection can influence the severity of RSV disease in children aged 0-5 years (n = 139) during the 2023/2024 season. At admission, serum samples were tested for IgG, IgA, and IgM antibodies against five SARS-CoV-2 antigens. Based on antibody profiles, children were classified into three groups: previously infected (IgG-positive), recently infected (IgM or IgA-positive only), and immunologically-naïve (negative for all antibody classes). Clinical outcomes, including duration of hospitalization, C-reactive protein (CRP) levels, need for oxygen therapy, and use of bronchodilators, antibiotics, and glucocorticoids, were compared across groups. SARS-CoV-2 seropositivity was found in 94 children (67.6%), 10 (7.2%) showed evidence of recent infection, and 35 (25.2%) were seronegative. The groups did not differ in hospitalization duration, CRP levels, or treatment needs. Although a higher proportion of children with recent infection required oxygen therapy (30%), this difference was not statistically significant. SARS-CoV-2 antibody concentrations did not correlate with disease severity. These findings suggest that prior or recent SARS-CoV-2 infection does not significantly influence RSV disease severity in young children.