On Friday, British researchers released early data that suggests while the omicron BA.2 subvariant is more transmissible than the original BA.1 variant, vaccines remain equally effective against both strains.

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What is the omicron BA.2 subvariant?

The BA.2 omicron subvariant is a descendant of the original BA.1 omicron variant that has caused massive global Covid-19 surges. Last week, the World Health Organization (WHO) urged researchers to prioritize the investigation of BA.2's characteristics to determine whether it poses new challenges for areas already overwhelmed by the pandemic.

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Like the original omicron variant, BA.2 has many mutations, including roughly 20 found in the area targeted by most vaccines. BA.2 also has unique mutations that are not found in BA.1, which could limit the effectiveness of monoclonal antibodies, according to Jeremy Luban, a professor of molecular medicine, biochemistry, and molecular pharmacology at UMass Medical School.

Further, scientists have found that BA.2 is harder to detect with PCR tests than BA.1. Although researchers were able to quickly differentiate BA.1 from the delta variant using a PCR test, the BA.2 subvariant does not possess the same "S gene target failure" seen in BA.1. As a result, BA.2 looks like the delta variant on the test, according to Wesley Long, a pathologist at Houston Methodist Hospital.

"It's not that the test doesn't detect it; it's just that it doesn't look like omicron," Long said. "Don't get the impression that 'stealth omicron' means we can't detect it. All of our PCR tests can still detect it."

Vaccines as effective against BA.2 as BA.1

The U.K. Health Security Agency on Friday released data that suggested that while the BA.2 subvariant appears to be growing faster than BA.1 because it is more transmissible, vaccines remain just as effective against BA.2 as they are against the original BA.1 omicron variant.

Although Covid-19 vaccines are not as capable of completely preventing infection against BA.1—which has largely driven the recent increase in breakthrough infections among vaccinated individuals—the vaccine still offers protection against severe disease, and booster doses have helped increase protection against infection, the researchers found.

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Specifically, the agency estimated that, among people who had received a booster dose at least two weeks prior, vaccine effectiveness against symptomatic disease was 63% for those infected with BA.1, and 70% for those infected with BA.2.

While that might make BA.2 seem like less of a threat when compared with BA.1, the full estimate ranges overlapped, STAT News reports.

How will BA.2 impact the pandemic?

At this point, BA.2 seemingly has not resulted in more severe disease, but it has shown signs of spreading more rapidly than BA.1, the New York Times reports.

BA.2's rapid spread suggests it could be able to outcompete BA.1. According to Jacob Lemieux, an infectious diseases physician at Massachusetts General Hospital, BA.2 has already displaced BA.1 in some countries, but "what we don't know, and still have almost no information on, is what impact this will have on case counts, on hospitalizations, on death."

"This may mean higher peak infections in places that have yet to peak, and a slowdown in the downward trends in places that have already experienced peak omicron," said Thomas Peacock, a virologist at Imperial College London.

According to Trevor Bedford, a virologist at the Fred Hutchinson Cancer Center, roughly 8% of cases in the United States are BA.2—but that figure is climbing fast.

While it is possible that BA.2 could result in another case surge, Nathan Grubaugh, an epidemiologist at the Yale University School of Public Health, said he believes it's more likely that we will see declining Covid-19 cases in the coming weeks.

"I'm fairly certain that it will become dominant in the U.S.," Grubaugh said, "but I don't yet know what that would mean for the pandemic." (Zimmer, New York Times, 1/30; Joseph, STAT News, 1/28)