We’ve also learned more about the nature of the threat. It has been an open question whether Omicron is a much less severe variant of the Covid virus than earlier strains, or if it has caused much less severe disease because it had run into a wall of immunity from vaccination and prior infection in the United States, Europe and parts of Asia with high vaccination rates. The deadly outbreak in Hong Kong answers that question: Covid remains ferocious, and Omicron is lethal in an immunologically naïve population, particularly among unvaccinated older people. This has caused the devastating surge in deaths there and helps explain why the United States continues to report around 1,000 deaths per day, the vast majority among people not up-to-date with vaccination.

Unfortunately, in the United States and many other high-income countries, vaccination has slowed to a trickle: It’s down in the United States by more than 95 percent from the peak of 4 million vaccinations a day. In some countries of Africa, where competing health risks are substantial and the health care infrastructure is stretched thin, vaccination rates are very low and are likely to remain so for many months.

The risks for the United States are clear. BA.2 is increasing and will likely soon account for most new cases in the country. Masks have come off and approximately 60 percent of Americans, including more than one third of people above age 65 — more than 15 million seniors — are not up-to-date with vaccination.