As BA.2 grows in the US, experts will look to other countries to predict its impact here – CBS Baltimore

(CNN) – After weeks of free fall, new Covid-19 cases are starting to level off in the US, as the subvariable BA.2 continues to climb.

BA.2 caused about 35% of cases in the United States last week, up from 22% the previous week, according to new estimates from the US Centers for Disease Control and Prevention, posted on Tuesday.

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At the same time, new Covid-19 cases are holding steady or increasing in about 19 states, according to data from Johns Hopkins University.

Some states see increases — New York, New Hampshire, Massachusetts, Vermont and New Jersey are in the northeastern regions where CDC estimates BA.2 is currently causing more than half of all new Covid-19 cases.

Health officials have warned that overall Covid-19 infection could rise across the US in a few weeks, paralleling trends in the UK and Europe.

“I wouldn’t be surprised at all if we saw some sort of increase,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a live interview on Tuesday. with Washington Post. “I don’t really see, unless something changes dramatically, that there’s going to be a big spike,” he said.

In the UK, where BA.2 now accounts for 85% of new infections, infections have increased by 20% from the previous week. Hospitalization rate increased by about 22% from last week. Deaths recorded within 28 days of a positive Covid-19 test increased by about 17%, according to most recent government number.

On Tuesday, the University of Washington’s Institute for Health Metrics and Evaluation, said its model does not predict a new increase in Covid-19 cases “similar to what we have seen in other countries”. region of Europe,” said Ali Mokdad, professor of global health at IHME, on Twitter. Instead, he said, their models show that after the end of March, the likelihood of Covid-19 transmission in the US will continue to decline.

Very contagious, but not more serious

Technically, BA.2 is classified as part of the Omicron family of viruses, but genetically it is very distinct, with about 40 mutations separating it from its cousins, BA.1. That makes it different from the original Omicron because Alpha, Beta and Delta are different.

It is more contagious than Omicron’s BA.1, which is already an extremely contagious virus with a basic reproduction number, or R-naught, of about 8, according to William Hanage, an epidemiologist at the School Harvard’s TH Chan Public Health, which means that on average, an infected person can transmit the disease to 8 other people.

Adrian Esterman, an epidemiologist at the University of South Australia, pegged the base reproduction number for BA.2 at around 12. “That puts it pretty close to measles, the most contagious disease we have. know,” he wrote on Twitter on March 10. .

Although BA.2 is more contagious, it does not appear to cause more severe illness. And although it escapes some of the immune protection created by vaccinations and previous infections, it does not appear to do so any more than BA.1.

Hanage says that at the population level, Omicron is much more manageable than Delta, but it’s not innocuous.

“The reason why Omicron BA.2 and BA.1 are such a problem is because of the large number of infections they cause,” said Hanage.

Will BA.2 cause waves or ripples?

The contours of the BA.2 wave look very different in different countries. BA.2 has caused an increase in the number of cases and deaths in Hong Kongwhere many seniors are hesitant to get vaccinated, but in South Africa, where it came after that country’s big BA.1 spike, it barely made a ripple – sending cases higher is high.

What BA.2 can do in the US remains an open question.

The UK has offered some clues about the trajectory of past variations. But there are key differences.

Working in their favor, the UK is more vaccinated than the US. Among people 12 years of age and older, 86% of the population received two doses of the vaccine, while more than two-thirds received a third or booster dose. In the US, 74% of people 12 years of age and older have received two doses of the vaccine, but only 46% have received a booster.

But the UK also has its own challenges, said Dr Carlos Del Rio, an infectious disease expert and executive dean of Emory School of Medicine. “They have a much older population than we do,” he said.

In the UK, 19% of people are over the age of 65, according to a UK government report. In the US, the elderly make up about 16% of the population.

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“The good news is that we had a very big Omicron growth spurt in the US,” said Del Rio. “Millions of people have been infected,” he said.

“And between the number of people infected and the number of people who have been vaccinated, we estimate that between 73% and 75% of the population has some degree of immunity,” he said.

Leaving about 25% of Americans vulnerable to the BA.2 virus because they can’t or don’t make antibodies.

“So my guess is we’re going to have a spike, but it won’t be a serious spike,” said Del Rio, though he still worries about the uninsured 25% of Americans. guard.

Clues from Qatar

Other intriguing clues about the shape of the BA.2 wave come from the Middle Eastern nation of Qatar, which has used a vaccine mix similar to that of the US.

Qatar has been living with BA.2 as the dominant virus since Christmas. They also saw a large Omicron increase that peaked around mid-January, followed by a sharp drop in the number of cases.

In a series of recent studies, Laith Abu-Raddad and his co-authors at Qatar’s Weill Cornell University, estimated the ability to protect conferred by mRNA vaccine as well as by previous infection.

They found that two doses of the mRNA vaccine provided moderate protection against symptoms — between 36% and 50%. But that protection only lasted for about four months. After four months, the protection became negligible, and after seven months, their studies found that vaccinated people were actually slightly more likely to get sick than those who weren’t. race, perhaps because they have a false sense of security.

“Vaccinated people don’t behave like unvaccinated people. You know, they think they’re protected, so this could expose them,” said Abu-Raddad.

He said: ‘Although the protection against infections has waned quite a bit over time, those vaccinated continue to be well protected against hospitalizations and deaths, during the storm. anger between 70% and 80%, he said, and that number has increased to about 90% with booster shots.

“The best thing anyone can do right now is buy a booster,” says Abu-Raddad. “The booster brings the protection against infection back to 60 per cent before,” he said. “But what is really amazing about the enhanced effect is that it virtually eliminates the risk of hospitalization and death from Covid-19,” he added.

In a separate study, Abu-Raddad and his team also looked at protection against BA.1 infection against BA.2. That protection was even stronger and more durable than two shots of the mRNA vaccine, in the range of 90%, he said.

“So that’s really another reason to think that even if there’s going to be a wave, it won’t really be as bad as people might fear,” he said.

Immunity after an infection declines much more slowly, he said. In a new study, where they followed people infected with the Alpha and Beta variants, they remained 50% protected against Omicron re-infection up to a year later.

The difference, Abu-Raddad suggests, is that immunity generated by the infection remains in the tissues of the mouth and nose, while the antibodies produced by an increase in body-wide vaccination will not increase. persisted in tissues that first encountered the virus.

Upcoming fourth dose for seniors?

One thing the Abu-Raddad study failed to reveal is the ability to maintain immunity in older people. Qatar is a young country. Less than 10% of the population is over 50, he said, so they can’t tell if the vaccine will continue to be as effective in the elderly as it is in younger people.

Del Rio suspects that the vaccine’s effectiveness in the elderly is weaker and faster than in younger people.

“I anticipate the CDC in the next week or two will recommend a fourth dose for people over 65. If you’re 65 and you’re infected, you can still get very sick even if you’ve been vaccinated,” he said.

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Jake Nichol

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