What to Know About BA.2.12.1, the New Variant Spreading in the U.S.

It’s only been about six months since the Omicron variant emerged and changed the landscape of the pandemic, sending case-counts soaring and causing breakthrough infections even among those who were fully vaccinated and boosted. The virus continues to keep scientists guessing, mutating into subvariants almost as fast as researchers can assign them names.

First there was BA.2, which became dominant in the U.S. earlier this spring. Now, another Omicron descendent known as BA.2.12.1 is accounting for a growing share of U.S. cases—about 36% of samples sequenced during the week ending April 30, according to the U.S. Centers for Disease Control and Prevention (CDC). Overall, average daily diagnoses have roughly doubled nationwide since early April.

Two other Omicron spinoffs, known as BA.4 and BA.5, are also currently spreading in South Africa, where they were first identified, and have been detected in other countries around the world.

It always takes time to learn how significant the emergence of new variants will be. Early data suggest the new Omicron relatives spread faster than BA.2, but they do not seem to cause more severe disease, the World Health Organization wrote in a report published April 27. CDC Director Dr. Rochelle Walensky recently gave a similarly reassuring message to reporters, saying that—though more research is needed—“we continue to believe that those who are vaccinated, and especially those who are boosted, continue to have strong protection against severe disease, even from BA.2.12.1.”

However, a pair of preliminary, not-yet-peer-reviewed studies—one from China and one from South Africa—suggest these newer Omicron subvariants are better than earlier strains at evading the immunity offered by vaccines and prior infections. That means even people who caught the original Omicron strain could be at risk of reinfection—but, as former U.S. Food and Drug Administration Commissioner Dr. Scott Gottlieb tweeted yesterday, those who are fully vaccinated and recently had COVID-19 seem to have stronger protection.

It’s not surprising that the virus continues to mutate; scientists have long predicted that would be the case. But as BA.2.12.1 works its way around the U.S., it should be a reminder that the pandemic is full of twists and turns. Everything we know about the virus and immunity to it can change. All it takes is a new variant.