Nirsevimab Effectiveness Against Severe RSV Infection in the Primary Care Setting

This study assesses the effectiveness of nirsevimab, a monoclonal antibody, in preventing medically attended respiratory syncytial virus-lower respiratory tract infections (RSV-LRTI) in a large primary care network in Spain, in both overall and catch-up infants under ten months of age.

The 2023–24 immunization campaign with nirsevimab in Spain targeted all infants born after April 1st, 2023. Those born after October 1st received it at birth in hospitals, while others received it through a catch-up program. The MEDIPRIM network of primary care centers recruited all infants with LRTI for RSV PCR testing and employed a test-negative design (TND) approach to estimate the effectiveness of nirsevimab.

The study included 160 infants, 141 (88%) of them received nirsevimab and 128 belonged to the catch-up group (88% received nirsevimab). Overall, RSV was detected in 44 infants (27.5%). Within the catch-up group, 37 (28.9%) were positive for RSV. The overall effectiveness was 75.8% (95% CI: 40.4-92.7), and 80.2% (95% CI: 44.3-95.4) in infants belonging to the catch-up group.

This study underscores the effectiveness of nirsevimab in preventing medically attended LRTI in infants in outpatient settings and emphasizes the importance of a catch-up immunization program to reduce the disease burden in primary care.