What We Know About COVID Subvariant BA.2, or ‘Stealth Omicron’


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For the most up-to-date news and information about the coronavirus pandemic, visit the WHO and CDC websites.

The BA.2 variant now accounts for the vast majority of new COVID-19 cases in the US, with the most recent data from the US Centers for Disease Control and Prevention pointing to BA.2 in 86% of new cases. 

On Wednesday, the CDC and Transportation Security Administration extended the mask requirement for public transportation through May 3, an additional two weeks. The mask mandate will remain while the CDC monitors BA.2 and “assesses the potential impact of the rise of cases on severe disease, including hospitalizations and deaths, and health care system capacity,” according to a statement.  

Scientists expected BA.2, also known as “stealth omicron,” to take hold in the US, but how big of a wave remains to be seen. In New York, state health officials are reporting subvariants of BA.2 itself, which appear to be even more transmissible and responsible for a growing number of cases in central New York.

COVID-19 cases are rising sharply in some areas, including New York and Philadelphia, which is reinstating its mask mandate. Currently, the number of Americans being hospitalized with COVID-19 and dying from the disease continues to decline. (However, hospitalization data lags behind case data.) 

While BA.2 is more transmissible than the original omicron (BA.1), which means BA.2 can infect more people, available data doesn’t suggest it causes more severe disease, according to a late February statement by the World Health Organization. Health officials expect vaccine effectiveness to be comparable to that of the original omicron, and it’s likely most people in the US have some immunity from COVID-19 vaccines, booster shots or prior infection with the virus.

To boost protection in people most vulnerable to severe disease, the CDC signed off in late March on second COVID-19 boosters for adults age 50 and up, as well as other individuals at higher risk.

Dr. Anthony Fauci, President Joe Biden’s chief medical adviser, told ABC News on April 10 that given the contagiousness of BA.2, as well as the drop in mitigation measures such as mask requirements: “We’re going to see an uptick.”

“What we’re hoping happens, and I believe it will, is that you won’t see a concomitant comparable increase in severity, in the sense of people requiring hospitalizations and deaths,” Fauci said. 

Here’s what we know about BA.2. Also, read more about when you should get your second booster if you’re eligible, and which COVID-19 vaccine you should choose.

Why is it called ‘stealth omicron’?

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. 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.

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What are the symptoms of BA.2? 

Data available currently suggests that BA.2 doesn’t cause more severe disease than the original omicron variant, even if it is more transmissible. (The WHO notes that the transmission difference between original omicron and stealth omicron is smaller than the difference between delta and omicron.)

There isn’t research available right now to suggest BA.2 causes different symptoms than the original omicron variant. For many people who catch COVID-19 (especially those who are fully vaccinated or boosted), COVID-19 symptoms resemble cold symptoms and you should stay home if you’re sick.

Read more: Is It Allergies or COVID? How to Tell the Difference

Is BA.2 more severe? Can you get omicron twice?

The WHO, considering all available the real-world data, concluded there’s no reported difference in severity between omicron BA.1 and BA.2, despite the latter’s growth advantage. 

“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 the significance of those mutations.

Like the original omicron, BA.2 makes our vaccines less protective against infection than earlier variants, but there isn’t data now to show whether 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 while. 

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.




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