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Why hasn't the BA.2 subvariant caused a big surge?

2022-04-06T18:08:34.625Z


The BA.2 subvariant of omicron is the dominant strain in the United States, but has not caused an imminent increase in the country.


What distinguishes the covid-19 BA.2 subvariant from the omicron?

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(CNN) --

The BA.2 subvariant of the coronavirus may actually be the "stealth variant."


The omicron subvariant caused as many as 3 out of 4 cases of covid-19 in the United States last week, according to the latest genomic surveillance from the US Centers for Disease Control and Prevention (CDC). in English), but so far there are no signs of an imminent increase in the country.

Even when the BA.2 subvariant has become the dominant strain, the overall number of cases continues to decline, says Dr. Jessica Justman, an epidemiologist at Columbia University's Mailman School of Public Health.

"This is a clear example of how these two trends are not necessarily linked," he says.

If things stay calm, as some models predict, it will be the first time a viral strain has taken hold in the US without causing a spike in covid-19 cases.

That's different from what's happening in the UK, some European countries and parts of Canada, where the arrival of the BA.2 subvariant coincided with a new wave of cases and hospitalizations.

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Andy Pekosz, who studies viruses at Johns Hopkins University, says that the new wave of cases in Europe may have more to do with the timing than with the characteristics of BA.2.

“What is recorded in Europe may be the result of the fact that they lifted their restrictions early, not so much that the BA.2 subvariant is there,” he says.

Pekosz says that many European countries abandoned some precautions when there was already a lot of virus circulating.

He says cases in the US fell faster and hit a lower level before BA.2 overtook its omicron cousin in the country.

"When you start low, it takes much longer to build up to a high number of cases," he says.

It also suggests that the US may not be entirely out of the woods with the BA.2 subvariant, as spring break and Easter break will mean more travel and more mixing of people from different parts of the country.

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Few signs of increased infections

The reason why the US is not experiencing the same increase in new BA.2 infections as in European countries remains controversial.

One of the theories is that positive cases are no longer seen in tests.

Data collected by the CDC and state health departments on positive tests is generated by laboratories;

they do not count the tests that people do at home.

And there has been a "dramatic shift" toward the use of home tests in the US, says Mara Aspinall, a professor at Arizona State University who has been estimating the volumes of home and lab tests.

According to her, in January and February there were between 1 million and 1.5 million covid-19 laboratory tests per day, but between 6 million and 8 million home tests.

A case detected by a home test is usually not reported unless later confirmed by a laboratory test.

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"I think there is no question that there is underreporting of positive cases," Aspinall said.

He believes this is, in part, why the CDC has shifted its pandemic measures to focus on hospitalizations and hospital capacity, and shifted its surveillance to wastewater, which measures levels of infection even when people are not tested.

Wastewater monitoring

However, even in the sewage there is not much to see.

If we focus on areas of the country with the highest BA.2 transmission, such as New York, sewage has only been modestly affected.

"It's still low when we look at the absolute numbers of viral copies in wastewater," said David Larson, an associate professor of public health at Syracuse University who helped create the state's wastewater dashboard.

"We're not at the level of the omicron [BA.1] surge, but it's increasing, and community spread is present, and transmission is still high," Larson said.

With more transmission of the virus, Larson says, authorities could see an increase in cases, but he's not sure.


It will depend on how bad people get from the infections.

"Cases measure access to treatment and access to testing," he said.

"So it's hard to predict what the cases will do."

There are also signs in San Francisco that the BA.2 subvariant may be gaining momentum, but it hasn't been a major one.

Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, says the Bay Area has been one of the most cautious areas in the country throughout the pandemic.

There are even some schools that remain closed because they are not willing to tolerate the risk.

He was surprised to see that San Francisco County recently ranked first for its seven-day average of new cases on the California Department of Public Health's COVID-19 dashboard.

"I had to rub my eyes," Chin-Hong said.

"I look at these trends almost every day, and San Francisco used to be at the bottom, and now it's at the top" in terms of new cases.

Test positivity is also on the rise.

But the increases you see are small.

"They're about to go up and like they're going to push forward," she said.

Chin-Hong says San Francisco is "superimmune" right now, with one of the highest vaccination rates in the country and a boost in antibodies from the recent wave of omicron subvariant BA.1 infections.

At the hospital where he works, things are quiet regarding covid-19.

It reminds him of what happened in Denmark and South Africa with the BA.2 subvariant, "which was basically nothing. There were no explosions of cases, no lives were lost."

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That won't stop people from feeling anxious, he said.

As cases rise, people will stay home and keep their children from going to school.

The anxiety stems from two things: PTSD from previous waves and a measure of freedom they don't want to give up, he said.

And while he's not ready to give the go-ahead, he thinks things may be better than people expect this time.

Are we moving forward thanks to failures?

If BA.2 doesn't wreak havoc, it may be because the United States did such a poor job of stopping the spread of omicron and the variants that preceded it, that we have failed "up," going wrong along the way and reaching a halt. level of immune protection.

The BA.1 and BA 1.1 variants proliferated in the US during the winter, when people abandoned the use of masks and largely resumed their vacation plans.

"That spike was just massive. It was like nothing we'd ever seen before," says Marina Matus, president and CEO of Biobot Analytics, a company that has been analyzing local county sewage and other US sewers since 2020. .

Matus says that the omicron and delta variants wiped out the population in a matter of weeks, while BA.2 has been dragging on for a few months.

"It's been going very, very slowly, and so far, we haven't seen an impact on the level of disease," he said.

Matus points to Ontario, which has higher viral load levels in its sewage, indicating more infections.

The omicron spike from that province with BA.1 a few months ago was not as high as the US and may not have left as much immunity in its wake.

"That data, to me, would say that, you know, they had a smaller omicron wave, and now [BA.2 is] picking up," he said.

The latest CDC estimate is that 95% of Americans have some level of immunity, either from infection or from vaccination.

About 43% of Americans are thought to have antibodies to the infection.

This immunity came at a high price: The United States remains the world leader in Covid-19 deaths, with more than 980,000, according to data from Johns Hopkins University.

Remembering this makes any respite from Covid-19 in the coming weeks bittersweet.

It may also be brief, as the world waits to see what other surprises the virus has in store for us.

coronavirus variants

Source: cnnespanol

All news articles on 2022-04-06

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