Viral replacement or proportional change? Respiratory surveillance as RSV prevention expands in Latin America

Maternal immunisation with RSVpreF and infant immunisation with the long-acting monoclonal antibodies nirsevimab and clesrovimab are reshaping prevention of respiratory syncytial virus (RSV) disease. Trials showed that RSVpreF reduced severe RSV-associated lower respiratory tract illness and that both antibodies reduced RSV-associated hospitalisations in infants.1–3 As RSV disease declines, however, a larger share of remaining respiratory admissions may test positive for other viruses. Distinguishing that proportional change from a true increase in their incidence is an urgent surveillance question for Latin America.