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 misconstructed 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 rip through the populace, there is more likely to be a lot of natural immunity to BA.2. That is one reason the US may not repeat the experience of the UK with BA.2: America’s first omicron wave was much worse than Britain’s, based on the number of deaths reported.

But in places that have to date been more on guard but are now relaxing rules, larger pockets of the population might have been untouched by omicron and are therefore more susceptible to BA.2.

“We may have this weird phenomena where the places that let omicron rage may be relatively protected, because they had that big omicron wave,” Lessler said. “But where omicron was somewhat contained, we are more likely to see a slight bump. Less of their protection has been from immunity, but has been from things they’ve been doing that they may be stopping doing.”

Varying vaccination rates will also continue to play a role in how different communities fare. “There’s considerable variation in vaccination rates and the like,” said William Hanage, a Harvard University epidemiologist, told me. “So I wouldn’t be surprised if we see a bump in some places that is more severe than others.”

Certain people will also carry more risk than others as BA.2 spreads. Elderly people are always most at higher risk of serious Covid-19 complications and, while about 60 percent of the over-65 population is boosted, new data published in the New England Journal of Medicine indicates the protection against infection conferred by a booster shot is fleeting.

Immunocompromised people also tend to see less of a benefit from vaccine shots, putting them at higher risk. The Biden administration has made more people eligible for booster shots to reduce the risks to people over 50 and immunity with immune conditions, but the extra may be brief.

Then there are children under 5, who are still not eligible for any Covid-19 vaccine. In general, they face much less risk from the virus than seniors. But that doesn’t mean their risk is zero. In particular, children of color are at higher risk of serious illness and other rare complications, such as extreme inflammation sometimes associated with an infection.

“Uncontrolled spread means more morbidity and more potential for long-term health consequences,” Arrianna Planey, a UNC health policy professor, told me. “In the absence of vaccinations for children under 5, this is especially concerning.”

So Covid-19 will continue to take its toll, particularly on the most vulnerable, even as life starts to return to something approximating normal.

“The challenge is how to find an equilibrium, where we can all observe sensible public health measures… without undue panic,” El-Sadr said, citing vaccinations and masking in crowded indoor places in particular.

Experts also fear that, in the long term, a small ripple rather than a massive BA.2 wave may provide a false sense of security. In a sense, we’re getting lucky: This new variant is taking over soon after an earlier version of the virus to which it is related and has not shown a strong ability to evade existing immunity for that reason.

Our luck might hold up — but that’s not assured. In a presentation to the FDA this week, virologist Trevor Bedford laid out two possible scenarios for the next year. In one scenario, BA.2 stays dominant and future cases are driven by predictable factors such as seasonality and waning immunity.

In that scenario, Covid-19 isn’t going away, but the virus isn’t throwing any curveballs at us.

But the other scenario is something similar to what happened to the first version of omicron: a “wildly divergent” iteration of the coronavirus emerges, with a high attack rate that threatens even people who have been vaccinated or previously infected.

Bedford said in his presentation he considered the first scenario to be more likely. But we have been surprised before.

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