Changing epidemic patterns of infectious diseases during and after COVID-19 pandemic in Taiwan.

Mitigation measures aimed at curbing the transmission of the severe acute respiratory syndrome coronavirus 2 effectively suppressed the occurrence of many respiratory infections other than coronavirus disease 2019. Several infections experienced a resurgence following the relaxation of non-pharmaceutical interventions, surpassing pre-pandemic levels in Taiwan. This phenomenon, known as immune debt, primarily affected respiratory infections in young children, including respiratory syncytial virus (RSV) infection. Infections transmitted by means other than droplets or contact did not exhibit significant changes in their epidemic patterns, such as varicella and Japanese encephalitis. Alterations in seasonality were noted for RSV infection and influenza, and these changes are also linked to immune debt. The recent emergence of severe pediatric pneumonia in northern China may be associated with immune debt and the rise of macrolide-resistant Mycoplasma pneumoniae associated with severe illness.