Abstract
BACKGROUND: Understanding the seasonality of human metapneumovirus (hMPV) and respiratory syncytial virus (RSV) is important for public health planning. It can support rationale for using another country data to model immunization strategies where seasonality data are lacking. While some studies have investigated (sub)-national seasonality drivers, this is the first to describe global seasonality for RSV and hMPV. METHODS: We included 26 countries with consistent reporting and >10 detections at the peak, after searching international databases and local reports. Weekly surveillance data from January 2022 to June 2024 were included. Viral activity was defined by comparing the 4-week moving average of the positivity rate to its annual average. "Seeding" events were the first 2 consecutive weeks with a statistically significant increase in detections. RESULTS: Most countries showed seasonal patterns of RSV and hMPV, except for some tropical countries. The RSV peak occurred systematically before the hMPV peak. On a Mercator projection, hMPV appeared to circulate in a counterclockwise manner, opposite to RSV. Although global information was incomplete, the first seeding events occurred in a short time in multiple countries with year-to-year variations. CONCLUSIONS: We have provided critical information on the circulation of hMPV and RSV. We only found 26 countries reporting suitable surveillance data in publicly accessible reports, which likely reflects true gaps in surveillance.