Two new omicron subvariants known as BA.4 and BA.5 are beginning to take hold in the U.S.
The two subvariants are now among several subvariants, or “sublineages,” of the omicron variant of COVID-19 being tracked by the CDC alongside BA.2.12.1, BA.2, B.1.1.529 and BA 1.1, among others.
"They were previously being included in one of the other subvariants because we are keeping an eye on them," Chicago Department of Public Health Commissioner Dr. Allison Arwady said Tuesday.
But the two have since been broken out into their own tracking on the CDC's website, according to the latest update on Tuesday.
The two variants combined first started making waves with their spread in South Africa, but in recent weeks have started growing in numbers in the U.S.
As of the latest update, BA.4 is making up 5.4% of COVID cases in the U.S. and BA.5 represents 7.6%.
In the Midwest, BA.5 makes up 8.1% of cases and BA.4 is 6.5%.
Still, BA.2.12.1 makes up a majority of cases across the country and in Illinois and Chicago. The highly contagious subvariant now makes up 62.2% of all U.S. cases, followed by BA.2, which currently makes up 24.8%.
But White House COVID-19 coordinator Dr. Ashish Jha told NBC News BA.4 and BA.5 will likely be dominant in the U.S. by the end of the summer or early fall.
Aside from being even more contagious than previous variants, scientists are tracking a mutation in BA.4 and BA.5, as well as BA.2.12.1, that could help it evade some immunity and cause reinfections.
Feeling out of the loop? We'll catch you up on the Chicago news you need to know. Sign up for the weekly Chicago Catch-Up newsletter.
A genetic trait that harkens back to the pandemic's past, known as a “delta mutation," appears to allow the BA.2.12.1 subvariant "to escape pre-existing immunity from vaccination and prior infection, especially if you were infected in the omicron wave," said Dr. Wesley Long, a pathologist at Houston Methodist in Texas. That's because the original omicron strain that swept the world didn’t have the mutation.
The genetic change is also present in the omicron relatives BA.4 and BA.5. Those have exactly the same mutation as delta, while BA.2.12.1 has one that's nearly identical.
This genetic change is bad news for people who caught the original omicron and thought that made them unlikely to get COVID-19 again soon. Although most people don't know for sure which variant caused their illness, the original omicron caused a giant wave of cases late last year and early this year.
Long said lab data suggests a prior infection with the original omicron is not very protective against reinfection with the new mutants, though the true risk of being reinfected no matter the variant is unique to every person and situation.
Chicago's data showed that last week, reinfections made up about 10% of new COVID cases, an increase from recent months, though health officials said many of the recent reinfections were in residents who contracted COVID some time ago, prior to the omicron wave.
In a twist, however, those sickened by delta previously may have some extra armor to ward off the new mutants. A study released before it was reviewed by other scientists, by researchers at Ohio State University, found that COVID patients in intensive care with delta infections induced antibodies that were better at neutralizing the new mutants than patients who caught the original omicron.
“The omicron infection antibody does not appear to protect well against the subvariants compared to delta,” said Dr. Shan-Lu Liu, a study author who co-directs the viruses and emerging pathogens program at Ohio State.
But Liu said the level of protection a delta infection provides depends partly on how long ago someone was ill. That's because immunity wanes over time.
People who got sick with delta shouldn’t think of themselves as invulnerable to the new subvariants, especially if they’re unvaccinated, Long said. “I wouldn’t say anyone is safe."
One bright spot? Booster shots can provide strong protection against the new mutants, Liu said. In general, vaccines and prior infection can protect people from the worst outcomes of COVID-19. At this point, scientists say, it's too early to know if the new mutants gaining ground in the U.S. will cause a significant uptick in new cases, hospitalizations and deaths.
Scientists are still trying to figure out how virulent these new mutants are.
Chicago's top doctor said the city is monitoring BA.4 and BA.5.
"It is more contagious," Arwady said Tuesday. "We're not seeing that it's making people more severely ill or showing up in different ways. But it's just another another subvariant of omicron."
Despite being more contagious, Arwady said she doesn't predict another surge is in store.
"Nothing about BA.4, BA.5 right now is making me concerned that it is likely to see a major surge but it continues to show us that the virus continues to evolve," she said.
She added that the city is "not seeing that it's making people more severely ill or showing up in different ways."
In the meantime, scientists expect the latest powerhouse mutants to spread quickly, since they are more transmissible than their predecessors.
