Still, it’s possible to predict what might happen as BA.5 ascends in the U.S. by looking at its effective reproduction number, or Rt—the average number of people whom each infected person then infects. The original version of Omicron, BA.1, “came in really hot,” Trevor Bedford told me. With an initial Rt of between 3 and 3.5, he estimates that it infected almost half the country in a few months, including 3 million to 4 million people a day at its peak. (These numbers are higher than the official counts, which have always been underestimates.) BA.2 was less ferocious: With an initial Rt of 1.6, it infected about one in 10 Americans in the spring, and peaked at roughly 500,000 daily infections. BA.4 and BA.5 have a slightly higher Rt but should “mostly mirror the BA.2 epidemic,” Bedford told me. It might not look that way on recent charts of new cases, where the close overlap between BA.4/BA.5’s rise and BA.2’s decline creates “the illusion of a plateau,” Bedford said, but the U.S. is nonetheless experiencing its third Omicron surge. He expects BA.5 to infect 10 to 15 percent of Americans over the next few months.

Of course, it doesn’t have to. The Biden administration, other political leaders, and many media figures have promoted laxer COVID policies, on the grounds that vaccines are still reducing the risk of death and hospitalization. But this stance is foolish for several reasons.

Even if the infection-fatality ratio for COVID—the risk that an infected person will die—falls to the level of seasonal flu, rare events stack up when the virus is allowed to spread unchecked. Bedford estimates that in such a scenario, COVID could still plausibly kill 100,000 Americans every year, “which is a lot!” he said. “It’s not like in the peak of the pandemic, but it’s a major health burden.” That burden is still mainly borne by the elderly; low-income workers; Black, Latino, and Indigenous Americans; and immunocompromised people. The entire Omicron dynasty may well have arisen from chronic infections in immunocompromised patients, in whose bodies the virus can evolve more rapidly, which suggests a self-interested case for preventing infections in this group, along with the more obvious moral rationale.