Table 2.

NPI definitions.

NPI	Definition
Primary schools closed	Most or all primary schools (ages 5/6 to 10/11) have moved all teaching online or have closed (including for school holidays).
Secondary schools closed	Most or all secondary schools (ages 10/11 to 17/18) have moved all teaching online or have closed (including for school holidays).
Universities closed	Most or all higher education institutions are on (summer) term-break, (Christmas) vacation, or have sent students away from the university town (e.g., by closing university accommodation). As a result, a large fraction of students will have left their term-time accommodation to live at their home addresses. We did not count online teaching as a university closure if students were still expected to be present in the university town because (i) this still allows (likely considerable) transmission from students mixing outside of teaching events, and (ii) universities usually moved various components of their schedule online throughout the analysis period in a gradual manner. Some of the regions of analysis did not contain universities. For these, we counted universities as closed throughout the period of analysis.
Night clubs closed	Most or all nightclubs, discos, and other late-night venues are closed.
Gastronomy closed	Most or all gastronomy establishments/venues (restaurants, pubs and cafes) are closed or limited to take-away.
Leisure and entertainment venues closed	A large fraction of leisure and entertainment venues are closed. Common examples include theatres, cinemas, concert halls, museums, gyms, dance studios, indoor skating rinks, bowling alleys, public baths, indoor play areas, escape games, casinos, billiard rooms, zoos and amusement parks.
Retail and close contact services closed	All nonessential retail shops are closed. Only those retail shops designated as essential may open; common examples are supermarkets, pharmacies, and gas stations. In addition, all nonessential services that require close contact between customers and service providers are closed. This includes beauticians, nail salons, massage parlours, and—in all countries but Italy— hairdressers, but not medical services.
Nighttime curfew	Individuals must stay indoors during evenings/nights. There are exemptions for limited reasons, such as emergencies or caregiving. Whenever regions in our dataset introduced nighttime curfews, they essentially always also implemented, or already had in place, several other NPIs listed in this table (night clubs and gastronomy closure). These are encoded as distinct NPIs in the data. In our results, we thus estimate the additional effect of a nighttime curfew on top of other active NPIs16.
Stricter mask-wearing policy	Mask-wearing is required in most or all shared/public spaces outside the home (inside and outside) where other people are present or where social distancing is not possible. Already before implementing this policy, all countries in our dataset had some less strict policies in place that required mask-wearing only in select public spaces (see Supplementary Note 4.1). The estimated effectiveness of this NPI thus shows the additional benefit of the stricter policy.
Public gatherings limited to ≤30, ≤10, 2 people or banned.	Gatherings in public spaces are limited to a certain number of people. The limits of 30 and 6 include all regulations with at least that level of strictness. For example, a ban on public gatherings of more than 15 people would be classified as “public gatherings limited to ≤30 people”.
Household mixing in private is limited to ≤30, ≤10, 2 people or banned.	Gatherings of individuals in private spaces are limited to a certain number of people. See the row above for additional explanations.