  As a reaction to the high infectiousness and lethality of the COVID-19 virus,
countries around the world have adopted drastic policy measures to contain the
pandemic. However, it remains unclear which effect these measures, so-called
non-pharmaceutical interventions (NPIs), have on the spread of the virus. In
this article, we use machine learning and apply drift detection methods in a
novel way to predict the time lag of policy interventions with respect to the
development of daily case numbers of COVID-19 across 9 European countries and
28 US states. Our analysis shows that there are, on average, more than two
weeks between NPI enactment and a drift in the case numbers.
