Stringency index in Belgium.

The stringency index is a composite measure based on nine response indicators, including school closures, workplace closures, and travel bans rescaled to a value from 0 to 100 (100 = strictest). If policies vary at the subnational level, the index shows the response level of the strictest subregion. The gray area indicates the period of data collection (adapted from Mathieu et al., 2023).