COVID-19: did preventive restrictions work?

During the ongoing COVID-19 pandemic, if a preventive restriction (PR) intended to arrest transmission of the virus is effective, we expect a decrease in the rate of transmission. If an effective PR is lifted or relaxed, the reverse is expected. We test this expectation in the history of PR imposition and relaxation in all countries based on available public database using a null model of spontaneous change in the rate of transmission independent of PRs. We use the stringency index defined earlier and available in public database to represent PR in different countries at different times. We found no negative correlation between standing stringency index of PR and change in slope of the local curve. A change in stringency index was significantly negatively correlated with change in slope, but it could explain only 6.1% of the variance in rates of transmission. The distribution of slope changes after imposing versus after relaxing PRs was highly overlapping with only a tail consisting of 4.5% PR impositions being clearly non-overlapping with PR relaxation. Non-parametrically, only 5.9% of PR impositions were associated with a reduction in the slope above the expectation of a null hypothesis. Globally, PRs have played a small role in the pandemic up to March 2021. This feedback needs to be considered in making policies for disease prevention in the further course of the COVID-19 pandemic as well as in any future threats of respiratory disease epidemics.