By Jason Fagone

The new BA.5 strain of the COVID-causing virus is “a different beast” from ones we’ve already seen — more infectious and better able to evade immune responses — and “we need to change our thinking” about how to defend against it, according to a data-packed Twitter thread posted Sunday by Dr. Bob Wachter, UCSF’s chair of medicine.

BA.5, a subvariant of the omicron family which has an altered version of the virus’s infamous “spike” protein, will soon become the dominant strain of the virus in the U.S., meaning that “its behavior will determine our fate for the next few months, until it either burns itself out by infecting so many people or is replaced by a variant that’s even better at infecting people,” Wachter wrote.

“Neither is a joyful scenario,” he added.

The number of new COVID cases per day has plateaued nationally and is down significantly since January. The same is true for the number of COVID hospitalizations in the UCSF health system, Wachter said. However, the true spread of COVID is harder to know these days, because so many people are testing themselves with at-home kits.

And BA.5 could cause a continued plateau, or even a new surge of infections and possibly hospitalizations, because it infects more easily and also is better at evading immune responses — even in vaccinated people, Wachter wrote.

While he stressed that vaccines and vaccine booster shots “remain hugely valuable in preventing a severe case” that might lead to hospitalization or death, the increased slipperiness of BA.5 means that existing vaccines will probably be less effective at preventing mild COVID cases or stopping transmission in the first place. Also, he wrote, prior infection by a different variant “no longer provides robust protection from reinfection” with BA.5.

What should a person do, then?

Wachter said it depends on how badly you want to avoid getting COVID. Personally, he said, he doesn’t want to risk getting long COVID and the debilitating symptoms that come with it, “So I still avoid indoor dining & will continue to wear an N95 in crowded indoor spaces until cases come way down.” Others might make different choices.

As for governments, he said, if BA.5 causes a surge in hospitalizations, “particularly if we also have staff shortages,” a return to mask mandates “would be the right call.” But Wachter acknowledged there would likely be fierce resistance to new mask-wearing requirements, especially outside of blue states, regardless of the danger.

“Most people have ditched their masks,” he wrote.