Onset of effects of non-pharmaceutical interventions on COVID-19 worldwide

Zeilinger, E. L.; Nader, I. W.; Jomar, D.; Zauchner, C.

During the initial phase of the global COVID-19 outbreak, most countries responded with non-pharmaceutical interventions (NPIs). The effectiveness of these NPIs has been investigated with simulation studies, that rely on assumptions and by empirical studies with few countries and controversial results. However, it has not been investigated in detail how long different NPIs need to be in place to take effect, or how long they should be in place for their maximum effect to unfold. We used global data and a non-parametric machine learning model to estimate the effects of NPIs in relation to how long they have been in place. Here we show that closure and regulation of schools was the most important NPI, associated with a pronounced effect about 10 days after implementation. Restrictions of mass gatherings and restrictions and regulations of businesses were found to have a more gradual effect, and social distancing was associated with a delayed effect starting about 18 days after implementation. Generally, effects increased until about 40 to 50 days after implementation. Our results can inform political decisions regarding the choice of NPIs and how long they need to be in place to take effect.