Effectiveness of long-acting monoclonal antibodies against laboratory-confirmed RSV in children aged < 24 months and hospitalised for severe acute respiratory infection, European pilot study, 2024 to 2025

Passive immunisation with long-acting monoclonal antibodies (nirsevimab) targeting the two antigenic subgroups A and B of respiratory syncytial virus (RSV) was authorised by the European Medicines Agency for use in the European Union on 31 October 2022 [1]. Nirsevimab is recommended for preventing lower respiratory tract infection caused by RSV in infants (aged < 12 months) in their first RSV season and in toddlers (aged < 24 months) vulnerable to severe RSV during the second season [2].

The Vaccine Effectiveness, Burden and Impact Studies (VEBIS) hospital network, set up in 2021 to measure effectiveness of influenza and COVID-19 vaccines in the hospital setting, included an additional objective to measure the effectiveness of nirsevimab against laboratory-confirmed RSV among children hospitalised for severe acute respiratory infection (SARI) during the 2024/25 season. The specific objectives of the study were to measure (i) the overall immunisation effectiveness (IE) with long-acting monoclonal antibodies in eligible children aged < 24 months by age group, and (ii) RSV IE by time since immunisation.