(The Hill) — About one out of three COVID-19 cases in the United States now stem from the BA.4 and BA.5 subvariants of the omicron strain, which are on their way to becoming the most dominant coronavirus strains in the country.

Data from the Centers for Disease Control and Prevention (CDC) estimates that 11.4 and 23.5 percent of U.S. COVID-19 cases are caused by the BA.4 and BA.5 omicron subvariants.

Early data also suggests these subvariants escape immunity more efficiently than previous lineages of the SARS-CoV-2 virus.

“The BA.4 and the BA.5 subvariants are about three to six times less sensitive to the neutralizing antibodies that the body makes in response to infection and vaccination,” David Montefiori, virologist and Duke University professor, told The Hill.

Montefiori, who has researched viruses like HIV for over 30 years, said BA.4 and BA.5 are essentially the same subvariant and current vaccines should be equally effective against both of them. The occurrence of these two subvariants is an indication of COVID-19 evolving to become less sensitive to antibodies, he added.

The BA.2.12.1 subvariant behind the recent rise in cases currently commands the greatest share at 56 percent. 

The two subvariants are eliciting some concerns about another waver of the coronavirus moving through the U.S.  

Cases have risen over the summer as many Americans have resumed the activities they took before the pandemic. But they have also hit a plateau of around 100,000 new cases a day. Experts believe vaccinations and booster shots have helped keep the figures lower.

In addition, deaths and hospitalizations have not spiked because of vaccines. More COVID-19 cases result in mild sicknesses.

This plateau of cases doesn’t include the two new sub-variants, for the most part.

At the start of June, less than 10 percent of cases were caused by BA.4 and BA.5, though that share has grown exponentially in the past few weeks.

David Dowdy, epidemiologist and professor at Johns Hopkins University, said the rise of BA.4 and BA.5 is the “natural evolution” of any infectious disease.

At the same time, most do not expect the newer subvariants to lead to more deaths as in previous spikes during the pandemic.

Dowdy said there is no strong data to suggest that the newer subvariants are deadlier or more transmissible than previous ones.

While evidence has suggested that BA.4 and BA.5 escape antibodies more effectively, available vaccines should still reduce the chances of death and hospitalization, even if they don’t prevent as many infections.

Despite the continued mutations, these subvariants are not drastically different from the original omicron variant.

Given that the strains currently circulating in the U.S. all descend from the omicron variant lineage, Dowdy said the COVID-19 virus is likely approaching its “ideal adaptation” for infecting humans.

“So it’s gonna be harder for it to mutate into a completely new variant that’s going to be a lot more contagious than the current one,” Dowdy said.

At the same time, he would not rule out the chances of another surge later this year.