Background For fighting the COVID-19 pandemic, countries used control measures of different severity, from ‘relaxed’ to lockdown. Drastic lockdown measures are considered more effective, but also have a negative impact on the economy. When comparing the financial value of lost lives to the losses of an economic disaster, the better option seems to be lockdown measures.
Methods We developed a new parameter, the effectiveness of control measures, calculated from the 2nd time derivative of daily case data, and normalised to the average of the daily case data during the effective phase; and also calculated from the derivative of the logarithm of the reproductive number. We calculated this parameter and two associated parameters, i.e. effectiveness, duration of effective phase, and ratio of the 2 former parameters, for 92 countries, states and provinces, whose effective phase ended the latest on 15 May 2020. We compared these effectiveness parameters, and also the mortality during and after the effective phase, for countries with and without lockdown measures by means of the Mann-Whitney test.
Results We did not find any statistically significant difference in the three effectiveness parameters, between countries with and without lockdown (p > 0.76; very small effect size). There was also no significant difference in mortality during the effective phase (p > 0.1; very small to small effect sizes), however a significant difference after the effective phase, with higher mortality for lockdown countries.
The effectiveness parameter derived from the daily case data correlated well with the parameter derived from the reproductive number (R2 = 0.9480). The average duration of the effective phase was 17.3 ± 10.5 days.
Conclusions The results indicate that lockdown measures are not necessarily superior to relaxed measures, which in turn are not necessarily a recipe for failure. Relaxed measures are, however, more economy-friendly. The higher mortality of lockdown countries is explained from the fact that, in our database, more lockdown countries than no-lockdown countries have higher mortality already during the effective phase that became significant only after the effective phase.