New Omicron Subvariants: What We Know About BA.4 and BA.5

Two new omicron subvariants known as BA.4 and BA.5 are gaining traction in the U.S., but how transmissible are they and what do we know about them?

Here's a breakdown of the newest mutations and what they could signal in the pandemic.

What are BA.4 and BA.5?

BA.4 and BA.5 are subvariants of omicron.

The two are among several subvariants, or “sublineages,” of the omicron variant of COVID-19, with the CDC also tracking 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.

Where have the variants been detected?

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%.

And while BA.2.12.1 makes up a majority of cases across the country and in Illinois and Chicago still, 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.

What makes these subvariants different?

Aside from being even more contagious than previous variants, scientists are tracking a mutation in BA.4 and BA.5 that could help it evade some immunity and cause reinfections.

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."

What works best for preventing the subvariants and could they cause another surge?

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.

"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," Arwady said Tuesday.

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.

“I’m hopeful that we don’t see a similar increase in hospitalizations that we’ve had in prior waves,” Long said. “But with COVID, any time you have lots of people being infected, it’s just a numbers game. Some of those people are going to be severe. Some of those people are going to need hospitalization. Some of them, unfortunately, are going to pass away.”

Are there specific symptoms associated with BA.4 and BA.5?

Experts say it's too early to tell if cases associated with subvariants have specific symptoms associated with them, or if they lead to longer-lasting symptoms.

"We are not at this point seeing this subvariant producing more or different long COVID symptoms," Arwady said. "But literally, we've only been following BA.4, BA.5 for a couple of weeks and so that's not really enough time to be able to fully address."

According to experts, most of the symptoms of recent subvariant are the same as other strains of COVID, including a stuffy nose, body aches, sore throat, sneezing, headache, coughing, fatigue and more.

Researchers in the UK found that runny nose and fatigue were slightly more prevalent in BA.2.12.1 cases, according to NBC News.