The BA.2.12.1 subvariant of Omicron is slowly becoming the dominant strain in the U.S., according to the latest data from the country's Center for Disease Control and Prevention (CDC).

The CDC said on May 20 that the new subvariant accounted for 47.5 percent of the total new cases found from May 8 to May 14 in the U.S., slightly behind the current mainstream subvariant, BA.2, which accounted for 50.9 percent.

The data is not based on precise statistics, but an estimation made by the bureau's algorithm.

People in the U.S. have suffered from a wave of BA.1.1 during last winter and this spring, and experienced a wave of BA.2 in March and April. Now, as BA.2.12.1 becomes the mainstream subvariant, the situation may get worse.

The new subvariant, first found in the U.S. in late 2021, is said to have better resistance against vaccines, thus it can spread faster than other subvariants.

A study conducted by scientists at Ohio State University found that the BA.2.12.1 subvariant is more resistant to the protection offered by mRNA vaccines, which were used by most Americans.

Many media outlets and experts said the Omicron subvariants are weaker than others and can cause less deaths. But some recent studies from Hong Kong and the U.S. suggest otherwise.

In addition to the BA.2.12.1 subvariant, the BA.4 subvariant is also closely monitored by the World Health Organization.

Patients of BA.2.12.1 and BA.4 have also been found in China, but they were all imported cases that caused no known community spread.