Why the Covid-19 BA2 variant may not cause a big wave of US cases

The BA.2 omicron subvariant of the coronavirus has been on the country’s radar for months — scientists conducting wastewater surveillance noticed it back in January. BA.2 first received widespread attention in early February as it appeared to drive a large wave of infections in the United Kingdom. And ever since, some health experts have been warning that this new iteration of the virus — even faster-spreading than the super-contagious original omicron variant — could create another wave in the pandemic.

So where is that wave? Case numbers, nationally and even at the state level, aren’t showing a surge. Across the US, the number of new cases reported every day has been flat for the last two weeks. Hospitalizations and deaths are still dropping from their peaks during the omicron wave. Some states are seeing a rise in cases — New York and Massachusetts in particular — but there are still few signs of major spikes. In Nevada, for example, while there has been a 73 percent increase in new cases over the last two weeks, the actual number of infections being reported is still quite low: 171 cases per day. Aside from the last few weeks, case numbers haven’t been that low since May of 2020.

None of the half dozen experts I talked to wanted to be too definitive about what’s going on. There’s still a chance that cases will spike in some places. For example, it’s too soon to know whether that 73 percent increase in Nevada’s daily cases is a blip or the start of exponential growth. But at this point, most of them think that the BA.2 wave may be more of a ripple.

This has happened before. Some worrisome variants have come and gone in the US without causing a nationwide wave: After the alpha variant was detected in late 2020, public health officials feared a new surge would arrive, but it never did. (The devastating winter wave of that year was mostly caused by the original virus.)

“The situation is very reminiscent of the alpha wave last year, which many people were worried would cause a major spring wave here in the US, but only registered as a blip on our decline from the winter wave,” said Spencer Fox, associate director of the University of Texas’s Covid-19 Modeling Consortium.

Other experts have similar expectations. “I do not believe that BA.2 will be associated with an explosive surge similar to what we saw before in January,” said Wafaa El-Sadr, a Columbia University epidemiologist.

Justin Lessler, who has helped lead Covid-19 modeling efforts at the University of North Carolina, told me the same: “It’s unlikely we would see in the US anything like an omicron or a delta wave.”

If this sounds like good news, it is — with a few caveats. BA.2 seems unlikely to spark a new wave of sickness and disruption so soon after omicron wreaked havoc. But that doesn’t mean the country is now in the clear.

People are taking fewer precautions than ever, which will give the virus chances to spread. There are individuals — the elderly, the immunocompromised, children under 5 who are not yet eligible for vaccination — who may not have much or any immunity if they do contract BA.2. And the immunity conferred by recent booster shots may not last very long, according to new data.

This next phase of the pandemic is not just about BA.2, Lessler said. It’s “BA.2 + masks off + waning immunity.”

Even if BA.2 is unlikely to spark a nationwide wave, it still poses dangers

It’s possible cases are being underreported as more people rely on at-home tests, the results of which they may not report to their local health department. BA.2 is also more likely to cause gastrointestinal distress, and it could be misconstrued as a stomach bug. But hospitalizations and deaths are less likely to be missed and they are still in steady decline. Wastewater samples could also show large quantities of virus if cases spike, even if more traditional surveillance shows a decline.

So why may BA.2 prove to be a bit of a “dud,” as Marc Johnson, who leads Missouri’s wastewater surveillance program, described it to me?

There is more immunity in the US population than ever before. About two-thirds of Americans have received two shots of the Covid-19 vaccines and 30 percent have received three shots. The recent omicron wave also spread a lot of natural immunity, which should provide protection against its cousin. More than 30 million Covid-19 cases were reported between December 1 and March 1.

Though BA.2 is more transmissible than the original omicron strain, it doesn’t appear to be able to escape the immunity conferred by a prior omicron infection, experts say. Vaccines also continue to provide a strong level of protection for most people.

Add it all up and, as Lessler put it, BA.2 “doesn’t have enough oomph to overcome all the extra immunity.”

In some parts of the United States, where there were few public health restrictions and more relaxed attitudes that allowed omicron to…