Changes in Respiratory Syncytial Virus-Associated Hospitalisations Epidemiology After Nirsevimab Introduction in Lyon, France.

BACKGROUND

Respiratory Syncytial Virus (RSV) is a major health concern, particularly for infants. In France, Nirsevimab, a long-acting monoclonal antibody to prevent RSV-associated lower respiratory tract infections (LRTI) was available from September 2023. We described RSV-associated LRTI hospitalisations during the 2023-2024 season among infants younger than six months born at the Hospices Civils de Lyon (HCL), and evaluated the effectiveness of Nirsevimab against RSV-LRTI hospitalisation.

METHODS

This observational study included infants born and hospitalised at the HCL during the 2023-2024 season, along with pre-COVID-19 and 2022-2023 seasons. Information on Nirsevimab immunisation status, clinical and perinatal variables were collected through routine care. Infants' characteristics and incidence rate of hospitalisation per 100 births during 2023-2024 were compared with the historical periods overall and by delay between birth and the onset of the RSV season. Nirsevimab effectiveness was computed by the screening method.

RESULTS

During the 2023-2024 season, 83 infants younger than six months were hospitalised with an RSV-associated LRTI. Compared with the historical periods (640 pre-COVID-19 and 123 in 2022-2023), these infants were older. Incidence rate for infants born during the period when immunisation was available were lower than the previous seasons; incidence rate ratios were 0.45 (95% confidence interval [CI]: 0.33; 0.62) in 2023-2024 compared with pre-COVID-19 period and 0.53 (95%CI: 0.36; 0.77) compared with 2022-2023 season. Nirsevimab effectiveness was 78.3% (95%CI: 55.9; 89.5) with a coverage of 79.3% in the two main HCL maternities.

CONCLUSIONS

High Nirsevimab coverage and effectiveness were estimated in a real-world setting. A change in the age distribution of RSV-associated LRTI hospitalisations in 2023-2024 was noted compared with historical seasons.