“BA.2 has a whole mess of new mutations that no one has tested,” Dr. Jeremy Luban, a virologist at the University of Massachusetts Chan Medical School in Worcester, told Nature in February. Like previous variants and subvariants, scientists need to observe the virus in the real world to determine how important those mutations are. Right now, the WHO is still monitoring BA.2 as a subvariant of the original omicron variant.
But as COVID-19 cases rise in other countries, some scientists caution that the US is once again underestimating the coronavirus.
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In a statement in late February, the World Health Organization said that while evidence does show it has a “growth advantage” over other versions of omicron — the dominant variant worldwide — an assessment of the available data didn’t find a difference in the severity of COVID-19 disease.
Here’s what we know about omicron sublineage BA.2.
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One early Danish study, which hasn’t been peer-reviewed, found no difference in hospitalization rates between the original omicron variant and BA.2. This is in contrast to another preliminary study from researchers in Japan, which found that BA.2 may be different enough from the original omicron variant to be considered a whole new variant and could also be more severe.
The WHO, however, considering all available the real-world data, concluded there’s no reported difference in severity between omicron BA.1 and BA.2, despite its growth advantage.
Why is it called ‘stealth omicron’?
Like the original omicron, BA.2 makes our vaccines less protective against infection than earlier variants, but there isn’t data now to show we’re worse off with BA.2. In a March 8 statement, the WHO said that while there are cases of people getting sick with BA.2 after they’ve already had COVID-19 caused by omicron, early data suggests that infection with BA.1 provides “substantial protection” against BA.2, at least for a period of time.
Is BA.2 more severe? Can you get omicron twice?
WHO Director-General Tedros Adhanom Ghebreyesus says we have learned the hard way that we’ve underestimated COVID-19 “at our peril.” However, that doesn’t mean people should be afraid just because a variant (or sublineage) has a new name. But in addition to sobering our attempt to live with COVID-19, a global rise in cases caused by any variant will lead to more deaths and also more opportunity for the coronavirus to mutate further.
Scientists need more information and time to watch how the current COVID-19 cases caused by omicron fall. More research is also needed to determine how well our COVID-19 treatments hold up, including Paxlovid. A preliminary study found that one of two monoclonal antibody treatments authorized for use against omicron doesn’t hold up. But Eli Lilly, which recently had an antibody therapy authorized by the US Food and Drug Administration for use against omicron, said the new treatment works against BA.2.
Read more: After 2 Years of COVID, Scientists Still Don’t Have Answers to These Vital Questions
Scientists in South Africa were able to quickly identify omicron as a new variant this winter because of the way it presents through PCR tests. The original omicron causes a dropped signal or marker on the test that sets it apart from delta, which was the dominant variant prior to omicron. Omicron BA.2, however, doesn’t have the same signal, called an S gene target failure. This makes it more stealthy, though genomic sequencing (which happens to about 10% of COVID-19 PCR tests in the US) will detect all omicron subvariants and coronavirus variants in general.
The culprit driving a rise in cases in some European countries and China is BA.2, or “stealth omicron,” which is one of the sublineages of omicron. (Yes, there are a lot, but only a few mean anything to the people who monitor their impact.) Scientists are watching BA.2 because it appears to have a transmission advantage over the original omicron, though it doesn’t appear to be causing more severe disease or posing a big threat to our immunity from vaccines or past illness.
In the US, masks are coming off as statewide mask mandates and city vaccine requirements expire. As COVID-19 case numbers and hospitalizations rates fall from their recording-breaking omicron peak this winter, pressure on states and the US Centers for Disease Control and Prevention has led to the loosening of pandemic restrictions and new ways to measure the threat of COVID-19.