Sunday, May 22, 2022

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

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Shreya Christina
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The BA.2 omicron subvariant of the coronavirus has been on the country’s radar for months — scientists conducting wastewater monitoring noted in January. BA.2 first gained widespread attention in early February as it appeared to be causing a major wave of infections in the UK. And since then, some health experts have warned that this new iteration of the virus — spreading even faster than the super-infectious original omicron variant — could spark another wave in the pandemic.

Where is that wave then? The number of cases, at the national and even the state level, is not increasing. Across the US, the number of new cases reported each day has been flat for the past two weeks. Hospital admissions and deaths are still falling off their tops during the microwave. Some states are seeing a rise in cases – New York and Massachusetts in particular – but there are still few signs of major spikes. In NevadaFor example, while there has been a 73 percent increase in new cases in the past two weeks, the actual number of reported infections is still quite low: 171 cases per day. Apart from the past few weeks, the case numbers have not been this low since May 2020.

None of the six experts I spoke to wanted to be too definitive about what’s going on. There is still a chance that cases will rise in some places. For example, it’s too early to know whether that 73 percent increase in Nevada’s daily cases is an outlier or the start of exponential growth. But right now, most of them think that the BA.2 wave might be more of a ripple.

This has happened before. Some worrisome variants have come and gone in the US without sparking a nationwide wave: After the alpha variant was discovered in late 2020, public health officials feared another wave might be coming, but it never happened. (That year’s devastating winter wave was largely caused by the original virus.)

“The situation is very reminiscent of last year’s alpha wave, which many people feared would trigger a big spring wave here in the US, but which was only recorded as a blip on our winter wave decline,” said Spencer Fox, associate director of the Covid-19 Modeling Consortium at the University of Texas.

Other experts have similar expectations. “I don’t believe BA.2 will be associated with an explosive wave comparable to what we saw earlier in January,” said Wafaa El-Sadr, an epidemiologist at Columbia University.

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

If this sounds good news, it is – with a few caveats. BA.2 seems unlikely to trigger another wave of disease and disruption so soon after omicron wreaked havoc. But that doesn’t mean the country is free now.

People are taking fewer precautions than ever, allowing the virus to spread. There are individuals — the elderly, immunocompromised children, children under the age of 5 who are not yet eligible for vaccination — who may not have much or no immunity when they contract BA.2. And the immunity conferred by recent booster shots may not last very long, according to new dates

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

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

Cases may be underreported as more people rely on home tests, the results of which may not be reported to their local health department. BA.2 also causes more gastrointestinal distress and can be misunderstood as a stomach flu. But hospitalizations and deaths are less likely to be missed and are still declining steadily. Wastewater samples can also show large amounts of viruses when cases peak, even if more traditional surveillance shows a decline.

So why might BA.2 turn out to be a bit of a “dud,” as Marc Johnson, who directs the Missouri wastewater monitoring program, described it to me?

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

Although BA.2 is more transmissible than the original omicron strain, it does not appear to be able to escape the immunity conferred by a previous omicron infection, experts say† Vaccines also still provide a high level of protection for most people.

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

In some parts of the United States, where there were few public health restrictions and a more relaxed attitude that allowed omicron to rip through the population, there is a higher chance that there is a lot of natural immunity to BA.2. That’s one of the reasons the US might not repeat the UK’s experience with BA.2: America’s first ommicron wave was much worse than Britain’s, based on the number of reported deaths

But in places that have been more wary until now but are now relaxing the rules, larger segments of the population would have been unaffected by omicron and therefore more susceptible to BA.2.

“We may have this weird phenomenon where the places where ommicron rage are relatively protected, because they had that big ommicron wave,” Lessler said. “But where ommicron was somewhat curtailed, we’re more likely to see a little bump. Less of their protection was from immunity, but from things they’ve done that they may have stopped doing.”

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

Certain people will also carry more risk than others as BA.2 spreads. The elderly are always at the highest risk of serious Covid-19 complications and, while about 60 percent of the population aged 65 and over gets a boost, new data published in the New England Journal of Medicine indicates that the protection against infection conferred by a booster injection is ephemeral.

Immunocompromised people also tend to benefit less from vaccinations, putting them at greater risk. The Biden administration has made more people eligible for booster shots to reduce the risks for those over 50 and with immune disorders, but the added immunity may be short-lived.

Then there are children under the age of 5, who still do not qualify for a Covid-19 vaccine. In general, they are much less at risk of the virus than seniors. But that doesn’t mean their risk is zero. Children of color in particular are at greater risk of serious illness and other rare complications, such as extreme inflammation, sometimes accompanied by an infection.

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

So Covid-19 will continue to take its toll, especially on the most vulnerable, even as life begins to return to something almost normal.

“The challenge is how to strike a balance, where we can all take sensible public health measures… without undue panic,” El-Sadr said, referring to vaccinations and masks especially in crowded indoor spaces.

Experts also fear that in the long run, a small ripple rather than a huge BA.2 wave could give a false sense of security. In a way, we’re lucky: this new variant is quickly taking over from an earlier version of the virus it’s related to and has therefore not shown a strong ability to evade existing immunity.

Our luck may last, but that’s not certain. In a presentation to the FDA this weekvirologist Trevor Bedford outlined two possible scenarios for the following year. In one scenario, BA.2 remains dominant and future cases are determined by predictable factors such as seasonality and declining immunity.

In that scenario, Covid-19 will not go away, but neither will the virus throw us at our feet.

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

Bedford said in his presentation that he considered the first scenario more likely. But we’ve been surprised before.

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