Is flu going around in China?

China's flu pattern is bimodal and spatially split. Northern China follows a typical temperate pattern with peaks from December through February. Southern China shows a more prolonged season, often running from autumn through winter, and sometimes produces a secondary summer peak driven by subtropical conditions. The two regions are tracked and reported separately in national surveillance.

The China National Influenza Center (CNIC), hosted by the Chinese Center for Disease Control and Prevention (China CDC), coordinates influenza surveillance across roughly 550 sentinel hospitals and over 400 network laboratories. CNIC produces weekly influenza surveillance reports and transmits aggregated data to WHO FluNet, where China's northern and southern regions are represented as distinct signals.

CNIC transmits weekly sentinel indicators to WHO FluNet via the Western Pacific Regional Office. China is notable for reporting the north and south separately, which FluNet publishes as two distinct curves. China also uses FluNet's LAB_RESULT_COMMENT field to publish weekly ILI-percentage data for each region, an unusually detailed contribution within the FluNet schema.

Climate, latitude, and contact patterns differ sharply between northern and southern China, producing genuinely different influenza curves. The northern signal follows temperate seasonality with winter peaks. The southern signal is more complex, with prolonged activity and occasional summer peaks. Reporting them separately preserves signal clarity that would otherwise be lost in a single national average.

CNIC classifies activity using ILI percentage against historical thresholds, reported separately for the north and south. Qualitative tiers (baseline, low, medium, high) are derived from those thresholds. Because the ILI% values are published through FluNet's LAB_RESULT_COMMENT field, the classification basis is unusually transparent compared with most FluNet contributors.