Cities that instituted quarantine, school closings, bans on public
gatherings and other such procedures early in the epidemic had peak
death rates 30 percent to 50 percent lower than those that did not.
That is from a study of the pandemic of 1918-1919 and here is more, from 2007. The best place to follow what is going on in Mexico — where such restrictions are now common — is ElUniversal. People in Mexico are dying of the flu every day; what is the chance that only the benign version of the virus crosses the border?