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How Much More Transmissible is BA.2 Than Omicron? Here's What Doctors Say

ChicagoBA.2 does not make people more sick than BA.1, which was less severe than the delta variant, according to a study from South Africa

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As the BA.2 omicron subvariant spreads in parts of the U.S., some are wondering about its transmissibility, specifically if BA.2 is more contagious than the original omicron strain.

BA.2 has been steadily growing as a proportion of the COVID variants circulating in the U.S. since Feb. 5, when it represented about 1% of genetically sequenced virus samples, according to data published this week by the Centers for Disease Control and Prevention.

Though BA.2 is rising in the U.S., leading public health officials are not expecting another dramatic surge in cases, largely due to the level of immunity from vaccination and the fierce outbreak during the winter omicron wave.

Public health officials in England have found that BA.2 is growing 80% faster than the earlier version of omicron, BA.1, according to a briefing paper published earlier this month. World Health Organization epidemiologist Maria Van Kerkhove has described BA.2 as the most transmissible COVID variant so far and said it’s sweeping the world. The subvariant now represents more than 80% of sequenced COVID samples worldwide, according to an international database.

BA.2 does not make people more sick than BA.1, which was less severe than the delta variant, according to a large real-world study from South Africa’s National Institute of Communicable Diseases. Reinfection with BA.2 — though possible — appears rare, according to a February study from Denmark’s Statens Serum Institut in Copenhagen. Neither study has been peer reviewed yet.

Several U.S. health experts agree BA.2 appears to be more transmissible than omicron.

"The best estimates are that it's about 1½ times more infectious or transmissible than omicron was. And, remember, omicron was quite a bit more transmissible than delta, which was more transmissible than alpha," Dr. Gregory Poland, head of Mayo Clinic's Vaccine Research Group, said in an article.

White House chief medical advisor Dr. Anthony Fauci said BA.2 is about 50% to 60% more transmissible than omicron, but it does not appear to be more severe.

"It does have increased transmission capability," Fauci previously said on ABC's "This Week." "However, when you look at the cases, they do not appear to be any more severe and they do not appear to evade immune responses either from vaccines or prior infections."

Northwestern's Dr. Michael Angarone, an associate professor of medicine in infectious diseases, said the increased transmissibility could be particularly strong in close contacts of those infected, but it's still too early to tell.

"We're still trying to figure out why are we seeing this rising number of cases in some of these countries in Europe and that is because there's something markedly different about the virus," he said. "So is it more transmissible? Are more people going to become infected from one infected individual? There might be some markers of that."

Experts also say so far, BA.2 does not appear to reduce the effectiveness of being fully vaccinated against COVID-19.

"...We are seeing a subvariant arise called BA.2 that's even more infectious," Poland said, in part. "This is going to continue to happen and infect every unvaccinated person until people are vaccinated and until they're wearing a mask. You can choose to ignore these facts ― these clear data ― but the virus could care less what we think. The virus is going to find people who do not have protective immunity and infect them."

NBC Chicago/CNBC/Associated Press
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