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Two new Omicron variants detected in the U.S. could spark another COVID wave. Research shows these people will fare best

Two new strains of COVID that appear to be more transmissible than even “stealth Omicron,” and that have the ability to evade antibodies from vaccination and prior infection, have arrived in the US—and they could mean a new wave is coming.

BA.4 and BA.5—like the original Omicron, BA.1—originated in South Africa. Cases are surging there despite the fact that almost all South Africans have been vaccinated or had COVID, Bloomberg reported last week. The country’s National Institute for Communicable Diseases reported nearly 4,000 new infections on Sunday alone. Of those who were tested for COVID, 22% received positive results. The World Health Organization initially recommended levels of below 5% for communities wishing to reopen after COVID’s first wave.

People who have been both vaccinated against COVID and infected with Omicron may very well get sick if they contract the subvariants. But they probably won’t require hospitalization or die, a top COVID researcher from South Africa told fortune.

“If you were vaccinated and had Omicron, your protection is decent, at least against severe disease,” said Alex Sigal, a professor at the Africa Health Research Institute in South Africa. He’s one of the authors on a new study that found BA.4 and BA.5 could result in a new wave of infection due to their ability to evade antibodies, both from vaccination and earlier infection.

“If anybody is protected, it should be these people,” he added.

That’s good news for many, but America’s vaccination rates are not where they could be. Around 66.2% of the total population is fully vaccinated, and only 45.8% have received a booster, according to the CDC. Children under 5 are still not eligible for the vaccine.

Others won’t be so fortunate. Sigal says those who have been infected with COVID prior to Omicron likely don’t have much immunity to BA.4 and BA.5. Those who were infected with Omicron but not vaccinated won’t have much immunity either. “It could go either way” for them, he said.

BA.4 and BA.5 appear to be more infectious than BA.2, also known as “stealth Omicron,” which was more infectious than the original Omicron, Bloomberg reported Thursday, citing South African COVID expert Tulio de Oliveira, the head of the institutes at the universities of KwaZulu-Natal and Stellenbosch.

On Friday, fortune was the first to report that both variants had arrived in the US, citing multiple COVID-19 researchers with access to Gisaid, an international research database that tracks changes in COVID and the flu virus. The earliest sample of BA.4 in the US was collected on March 30. The earliest sample of BA.5 in the US was collected March 29.

A new BA.4/BA.5 wave is “a strong possibility,” given the subvariants’ increased transmissibility and their ability to evade immunity, Sigal and his team wrote in their new study.

But Sigal doesn’t expect a huge wave, given that Omicron infected so many worldwide. He also doesn’t expect “a very severe wave in terms of disease severity,” he said, given the measure of protection—albeit reduced—that vaccination and/or prior Omicron infection will offer.

“infections? Yes,” he said. “Disease severity? Not so much.”

Sigal and his team tested the new subvariants against blood samples from individuals who had been vaccinated with shots from Pfizer or Johnson & Johnson, and who had experienced a breakthrough BA.1 infection, as well as those who had been previously infected with BA.1 but had not been vaccinated.

They found that those who had been previously infected but not vaccinated experienced a nearly eightfold drop in neutralizing antibodies when exposed to the new subvariants. Those who had been vaccinated and previously infected saw a more mild threefold decrease, according to the study.

Sigal said he was surprised by the study’s results. He didn’t expect BA.4 and BA.5 to escape immunity so well, especially considering that the variants have only two changes when compared to the original Omicron.

“But apparently those are big changes,” he said.

So far symptoms of the new variants seem pretty similar to the typical Omicron symptoms, which include fever, loss of smell, and malaise.

“I haven’t seen early symptoms of respiratory distress, the major COVID-specific symptom that makes this disease so dangerous,” he said. “It doesn’t feel nice, but there’s less chance of dying.”

There’s “good evidence” that COVID is becoming milder with time, he said, due to the fact that it’s not infecting the lower respiratory tract, where permanent damage can happen and dangerous low blood oxygen saturations can be triggered. So far, newer COVID variants reside in the upper respiratory tract, where they’re unlikely to cause serious illness.

Until recently, experts thought that a new, very different variant would be required to cause a wave, as was the case with Delta. But now subvariants “seem to be able to make a new wave,” Sigal said.

Subvariants—including BA.4 and BA.5—worry him less than new variants.

“They’re not so different from what was there before. They’re not going to do a huge amount of damage even though they might do a lot of infection,” he said. “When I see something completely different, that’s when it’s time to really get concerned.”

This story was originally featured on Fortune.com

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