If you've had omicron before, are you safe from infection by the new variants?

When it comes to omicron, one thing seems certain to bioinformatician Shishi Luo: Another surge will occur.

That's because new versions of omicron are emerging — here in the United States and in other parts of the world as well, like South Africa.

These new variants have a key set of mutations which enable them to spread even faster than the previous versions of omicron.

So people are wondering: If I had omicron once, can I get it again?

Now two preliminary studies, published online this week, start to answer that question. And the results show just how quickly omicron can mutate and overcome the defenses our immune systems put up.

How the variants are faring in the U.S. and South Africa

Before we get to the studies, let's look at what these variants are doing in the U.S. and South Africa.

In the U.S. a new version of omicron called BA.2.12.1 emerged in central New York state last month, where it caused a steep rise in cases. BA.2.12.1 is now found across the country, and It spreads about 50% faster each week than the omicron BA.2, which has been dominant in the U.S. variant.

"Given how this [new] variant is rising now in the U.S. it will definitely come to dominate here," says Luo. "And so I think the question is how high will the surge go before it peaks? How big of a bump will it be? I don't know the answer. It really just depends on people's behavior."

In South Africa, two of these new omicron variants, known as BA.4 and BA.5, are causing a fifth wave of cases. In the past two weeks, cases there have nearly quadrupled, from about 1,200 each day to 4,600 each day. And the positivity rate jumped from about 8% to 18%.

Omicron is a 'master player'

What these new variants show is just how wily omicron is.

"In terms of the ability to evade antibody activity, omicron is a master player. It's way more efficient than all the previous variants," says virologist Pei-Yong Shi at the University of Texas Medical Branch at Galveston, who wasn't involved in the newly published studies. "Like in this case, you need just a key mutation that can totally flip things around."

The two new studies start to explain why, all of a sudden, these new variants have started to spread so quickly. The answer boils down to one key factor: Their mutations allow them to re-infect people who have already had an omicron infection. This reinfection risk may be higher for people who are not vaccinated.

In the studies, researchers took blood from people infected with the original omicron variant, BA.1, and looked to see if the antibodies in the blood could neutralize newer versions of omicron, including the one that emerged in New York state (BA.2.12.2) or the two variants surging in South Africa (BA.4 and BA.5).

All people infected with omicron BA.1 had antibodies able to neutralize BA.1. But that potency decreased dramatically against the new variants (BA.2.12.2, BA.4 and BA.5). And how much it declined depended heavily on whether the people were vaccinated.

For people not vaccinated, their antibodies ability to neutralize BA.4 and BA.5 dropped by nearly 8 times, compared to the activity against BA.1, both studies reported.

"Neutralization capacity ... after BA.4/5 was very low," immunologist Alex Sigal, who led one of the studies, wrote on Twitter. Against BA.2.12.1, the potency dropped by about 4 times, researchers at Peking University reported.

"Together, our results indicate that Omicron can evolve mutations to specifically evade ... immunity elicited by BA.1 [omicron] infections," biophysicist Sunny Xie and his colleagues from Peking University write in one of the studies.

What vaccines can and can't do

"The situation was better in the vaccinated breakthrough cases," added Sigal, who's at the Africa Health Research Institute. For people immunized, either with the Pfizer vaccine or the Johnson & Johnson vaccine, the neutralization ability dropped only 3 fold against BA.4 and BA.5, compared to the potency against BA.1. These people also had more neutralization capacity against BA.1 to begin with. So in the end, they had, on average, about 5 times the neutralization potency against the new variants, compared to people who weren't vaccinated before the infection.

"The data shows, again and again, that the vaccine still has tremendous benefits," says virologist Pei-Yong Shi in Galveston, Texas.

Nevertheless, Sigal believes this decline in antibody potency is enough "to cause trouble and lead to an infection wave" – like in South Africa, where only about a third of the population is immunized.

Bioinformatician Tulio de Oliveria agrees. "Previous infections with Omicron BA.1 will not be sufficient to prevent a second infection with BA.4 and BA.5," de Oliveria, who's at the Center for Epidemic Response and Innovation in Durban, wrote on Twitter.

"Some scientists & science communicators are convinced that one needs a new variant to cause a new wave," de Oliveira added. "Delta caused a long wave with multiple lineages. Omicron is causing waves with BA.1, BA.2, BA.2.12.1, BA.4 & BA.5."

Here in the U.S., both BA.4 and BA.5 are extremely rare. No one knows if they will be able to compete with BA.2.12.2, which accounts for about a third of all cases in the U.S., the Centers for Disease Control and Prevention estimates. "Cases of BA.2.12.2 are growing exponentially," says Shishi Luo at Helix. "Depending on the rate of that exponential growth, we could start seeing a really sharp increase in cases across the country happening in the next month or so."

Copyright 2022 NPR. To see more, visit https://www.npr.org.