What could have happened: Officials could have put in place effective and early mitigation strategies.

The rest of the world could have understood the virus as Japanese officials did. Based on their understanding, which was arrived at in February 2020, that Covid was airborne, spread without symptoms and driven by clusters, by early March they were recommending mask-wearing, emphasizing the need for ventilation and advising the public to avoid the three-Cs: closed spaces, crowded places and close-contact settings.

Americans on the other hand were disinfecting their groceries, and the W.H.O. kept emphasizing hand-washing and social distancing, or remaining six feet apart. Japan has had about 25,000 Covid deaths, which would be the equivalent of just under 66,000 in a country the size of the United States.

Mass testing could have detected people who were infectious before they even knew they were sick and sometimes those who never had symptoms at all. Ventilation and air filtration could have kept indoor spaces safer.

Instead of closing parks, activities could have been moved outside weather permitting, since natural ventilation more effectively dissipates the virus. The key role of masks would have been understood earlier, along with the benefits of higher quality masks.