On Nov. 23, 2023, the World Health Organization (WHO) announced that it was monitoring data from Chinese surveillance systems that had shown an increase in respiratory illness in children in northern China.

Chinese authorities attributed this increase to lifting of COVID-19 restrictions and circulating known pathogens such as influenza, Mycoplasma pneumoniae, respiratory syncytial virus (RSV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).