BA.4 and BA.5 are new Omicron sub-variants: what you need to know


lIt only took about a month for BA.2.12.1, an Omicron subvariant, to cause the most new COVID-19 cases in the US since scientists first saw it in the country. But even newer versions of the Omicron variant are rapidly spreading across the US and are poised to surpass previous versions of the virus, reinfect millions of Americans and extend the country’s current COVID-19 wave.

BA.4 and BA.5 now account for more than 21% of new cases in the US, according to estimates from the US Centers for Disease Control and Prevention (CDC) on June 11. These two new sub-variants have evolved from the Omicron line to be even more contagious and can evade immunity from a previous infection or vaccination, experts say. This means that people could be reinfected even if they had Omicron earlier this year.

Here’s what you need to know about the latest Omicron sub-variants.

They are built to escape immunity

Omicron BA.4 and BA.5 were first identified in South Africa in January and February 2022, respectively. BA.2.12.1, meanwhile, evolved from BA.2 in the US, and scientists from the New York State Department of Health identified the first cases caused by this in the country in April.

All three subvariants have a similar mutation that sets them apart from older versions of Omicron, said Marc Johnson, a professor of microbiology and immunology at the University of Missouri who leads the state’s wastewater monitoring program. “There’s clearly agreement on how to evade the immune system,” he says.

These newer versions of Omicron can bypass antibodies created by previous vaccination or previous infection, said Paul Bieniasz, a professor at Rockefeller University who studies viral evolution. Several research groups – including a team at Columbia University, a consortium in Japan and an international group of South African scientists – have tested antibodies from previous Omicron infections against BA.4 and BA.5. All three studies have shown that such antibodies are several times more protective against Omicron BA.1 or BA.2, which are older versions of this variant, than against BA.4 or BA.5.

While these studies have not yet been peer-reviewed, scientists like Bieniasz view them as part of an expected trend in the ongoing evolution of the coronavirus. Future variants will have “more and more mutations that allow them to evade the antibodies we generate in response to vaccination and infection,” he says.

Some treatments are not as effective against them

The newer subvariants can also bypass monoclonal antibody treatments, which use lab-made immune system proteins developed from previous strains of SARS-CoV-2. “Most of those antibodies that were made are now obsolete,” Bieniasz says. Only one such treatment from Eli Lilly, specifically designed to work against Omicron, is now effective and in use. Still, other treatments, such as the antiviral drug Paxlovid, can help minimize the severe symptoms of Omicron infections.

They are more contagious, but it is still unclear whether they cause a more serious illness

Limited data is available so far on the severity of the newer subvariants, although scientists are optimistic based on reports from South Africa, where there were fewer hospitalizations and deaths. during his BA.4 and BA.5 waves compared to BA.1.

However, it is clear that BA.4, BA.5 and BA.2.12.1 are more contagious than previous versions of Omicron, allowing them to spread even faster. According to CDC estimates, BA.4 and BA.5 grew from causing about 1% of new COVID-19 cases nationwide in the first week of May to 22% of new cases in the week ending on June 11. BA.2.12.1 has exploded in the same way: it now causes an estimated 64% of new infections in the US and has caused the most new cases nationwide since mid-May.

Data from Helix, a genomics and viral surveillance company, also shows that BA.4, BA.5 and BA.2.12.1 are gaining ground, while older versions of Omicron are declining. The US already had a BA.1 wave and is now in the midst of a BA.2 wave, said Shishi Luo, associate director of bioinformatics and infectious diseases at Helix. BA.4 and BA.5 could trigger another wave on top of this BA.2 peak, she says.

It’s unclear which strain will dominate the US next time

Luo and other experts are looking at whether one or two of these Omicron sub-variants will outperform the others. While BA.4 and BA.5 have caused new COVID-19 peaks in other countries, these sub-variants have yet to compete directly with BA.2.12.1. Early data from the UK suggests that BA.4 and BA.5 may spread slightly faster than BA.2.12.1, but the landscape is unclear.

BA.4, BA.5 and BA.2.12.1 “all compete for the same people because they have about the same advantage,” Johnson says. His team’s wastewater monitoring network in Missouri shows that BA.4 and BA.5 cause more cases in some places, while BA.2.12.1 causes more cases in others. However, the regions dominated by BA.2.12.1 show a greater increase in the number of cases, he says. This pattern contradicts other reports from BA.4 and BA.5 which adopt BA.2.12.1.

Different versions of Omicron could become the dominant species in different parts of the country, Bieniasz says. For example, in the northeast, where a wave caused by BA.2.12.1 appears to have already peaked, BA.4 and BA.5 may gain less foothold, while they are more common in the south and west. People’s behaviors, such as the choices to hold large gatherings or travel, can also play a role in which variation is best when different species are “closely matched in their fitness,” he says.

One thing is clear, however: many Americans are susceptible to reinfection from these subvariants. “We can expect to be re-infected,” Luo says. “And every time we’re infected, it’s a hassle at best. And at worst, it can lead to debilitating symptoms,” she adds, pointing to the risk of Lung COVID — which, according to recent studies, even occurs in people who have been vaccinated.

“We didn’t really realize how slippery this virus would be,” Bieniasz says. He expects the coronavirus to continue to evolve around the immune system’s defense mechanisms. New vaccine candidates, such as the Omicron-specific booster developed by Moderna, may be needed to increase protection against further reinfections.

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