New variants are poised to keep Covid-19 circulation at high levels throughout the summer


The next influx of infections will likely come from new subvariants of Omicron BA.4 and BA.5, two closely related viruses that were first characterized in South Africa and landed in the United States around the late March, according to the Gene Sequence Sharing Site. GISAID.

These variants are gaining ground against BA.2, especially in the center of the country. Recent research suggests that they escape the immunity created by vaccines and past infections.

According to the latest updates from the US Centers for Disease Control and Prevention and genomics company Helix, BA.4 and BA.5 together accounted for about 6-7% of new infections in the United States at the end of May.

“This is a serious threat,” Dr. David Ho, a professor of microbiology and immunology at Columbia University in New York, wrote in an email. “Just a month ago it was 0.02%.”

BA.4 has been detected in at least 30 countries and BA.5 has been sampled in 32 countries, according to the Outbreak.info website, which is operated by the Scripps Research Institute.

Ho and his co-authors recently tested antibodies from the blood of vaccinated and boosted people, as well as antibodies from people who had recovered from breakthrough Covid-19 infections, against the modified BA.4 and BA.5 viruses. in laboratory. In each case, they found a power drop against BA.4 and BA.5.

They found that BA.4 and BA.5 viruses are more than four times more likely to evade antibodies in vaccinated and vaccinated people than BA.2 viruses.

No more breakthrough infections

All of this means that BA.4 and BA.5 are more likely to cause breakthrough infections, even in people who have had Covid-19 before.

Without improved vaccines or boosters, Ho expects many Americans to fall ill in the coming weeks or months. “I think we will see a lot of infections but not necessarily more serious illnesses or deaths,” he said.

Ho’s research is published as a preprint, which means it has not been reviewed by outside experts or published in a medical journal.

South Africa, which is ahead of the United States in its BA.4/BA.5 cycle, saw infections rise but did not experience a corresponding increase in deaths, said Shishi Luo, associate director of the bioinformatics and infectious diseases at Helix.

“So I think if we extrapolate from South Africa, what we will see in the United States is that BA.4 and BA.5 will increase, because they have competitive advantages over existing strains, but let’s cross our fingers, it’s not going to lead to more serious results,” Luo said.

One question variant hunters have asked is whether BA.4 and BA.5 can outperform BA.2.12.1, the highly contagious strain that is currently the leading cause of Covid-19 infections in the United States.

These branches of the Omicron family tree rose to prominence around the same time; BA.2.12.1 quickly took over the United States while BA.4 and BA.5 took hold in South Africa.

They share some similarities, including changes at location 452 in their genome, a genetic address known to help variants evade our immunity.

Viruses collide

“It’s like boxing,” said Dr. Alex Greninger, associate director of the University of Washington’s Clinical Virology Laboratory. “It’s like the national champion of South Africa taking on the national champion of the United States.

“You don’t know how to classify them if they’ve never fought,” he says.

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But BA.4 and BA.5 opposed BA.2.12.1 in other parts of the world, such as the UK. There, the scientists found that the time it took for the number of infections caused by one variant to double was about 5.5 days for BA.2.12.1 and about a day less for BA.4 and BA. 5, indicating that these viruses spread faster. . The doubling times were included in a recent technical report from the UK Health Security Agency.

“The betting favorite now suggests BA.4 and BA.5 could knock out BA.2.12.1,” Greninger said.

Ho and his team think they may have figured out what gives BA.4 and BA.5 an extra advantage.

In addition to all the changes in other Omicron variants that help them bypass our vaccines, these viruses have passed an F486V mutation. This is a great change that helps disguise them from our immune system. In the past, this had a downside: it made the virus spike less likely to bind to our cells, so they were less competitive. But BA.4 and BA.5 have an additional mutation, called R493Q, which restores their ability to bind to cells, restoring their ability to infect us.

Although BA.4 and BA.5 seem capable of dominating BA.2.12.1, they have not faced each other in the United States, and the fitness of these varieties depends very much on the playing field. The variants do not follow a rule book.

But for the next few months, experts say, there will just be plenty of Covid-19 around us.

“For the summer, before the winter, I expect these viruses to be at relatively high levels,” Greninger said. “Just the number of cases, the pure disruption to the workforce – It’s just a very heavy disease burden.”


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