In the spring 2020 wave of the Covid-19 pandemic many countries suffered from a fast exponential rise of daily infection numbers, clearly visible in logarithmic scale as steep linear rise. Most governments counteracted with severe obligatory restrictions of social life, vulgo "lockdowns", in order to attenuate the steepness of rise or even bend the infection curve downward. Finally it went down, but whether this was actually due to lockdowns was widely discussed.
Comment on Bendavid E, Oh Ch,, Battacharya J, Ioannidis JPA Assessing Mandatory Stay-at-Home and Business Closure Effects on the Spread of Covid-19 doi:10.1111/ECI.13484.