EXPLAINER: BA.2 variant takes over. What's known about it?

In the latest battle of the coronavirus mutants, an extra-contagious version of omicron has taken over the world.

The coronavirus version known as BA.2 is now dominant in at least 68 countries, including the United States.

The World Health Organization says it makes up about 94% of sequenced omicron cases submitted to an international coronavirus database in the most recent week. And the Centers for Disease Control and Prevention says it was responsible for 72% of new U.S. infections last week.

Dr. Wesley Long, a pathologist at Houston Methodist in Texas, said he’s seen BA.2 quickly become dominant in his medical system. At the end of last week, the variant was responsible for more than three-quarters of cases in Houston Methodist hospitals. Less than two weeks earlier, 1% to 3% of cases were caused by BA.2.

“It’s not terribly surprising because it is more contagious” than the original omicron, Long said.

As the variant advances, scientists are learning more about it. But they still don’t know exactly how it will affect the trajectory of the pandemic.

WHAT’S KNOWN

BA.2 has lots of mutations. It’s been dubbed “stealth omicron” because it lacks a genetic quirk of the original omicron that allowed health officials to rapidly differentiate it from the delta variant using a certain PCR test.

One reason BA.2 has gained ground, scientists say, is that it’s about 30% more contagious than the original omicron. In rare cases, research shows it can sicken people even if they’ve already had an omicron infection — although it doesn’t seem to cause more severe disease.

Vaccines appear equally effective against both types of omicron. For both, vaccination plus a booster offers strong protection against severe illness and death.

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