As the BA.5 variant takes over, Covid death numbers have become an object lesson in why raw data is often misleading.

New variants can infect people who had Covid-19 as recently as a few months ago.

The delta variant is dangerous. A third vaccine dose could be helpful for those with weaker immune systems, but giving third doses to healthy people would be wildly counterproductive.

Vaccinate. Do it quickly.

New models suggest that if vaccination rates only reach 68 percent and people refuse to wear masks, this autumn could be dangerous—particularly given the spread of the highly infectious delta variant.

India’s severe outbreak shows why the world needs early warning systems for variants that could evade vaccines.