As the coronavirus continues to infect the nation, the BA.4 and BA.5 omicron subvariants are now the predominant strains in the Midwest, according to Chicago's top doctor.
Chicago Department of Public Health Commissioner Dr. Allison Arwady said in a Facebook Live event Tuesday that the prevalent omicron strains are quickly shifting, with the latest two notably more infectious.
"The majority of the cases that we're seeing are either BA.4 or BA.5, and just as a reminder, BA.4, BA.5 are more contagious," Arwady said.
With these two variants, Arwady noted that, in some cases, those previously infected with omicron "early on" have become reinfected with BA.4 and BA.5. However, COVID-19 vaccinations have continued to prevent severe hospitalization and death, she said.
"But there's so much transmission that's still going on that we are seeing the virus mutate and change very quickly," Arwady said.
Chicago's head doctor explained that the Midwest is ahead of the northeastern part of the U.S. in recording BA.4 and BA.5 cases. Nationwide, though, a combination of the two variants have become the majority strains.
In the Midwest as of June 25, BA.4 made up 16.9% of cases while BA.5% accounted for 39.4%. Nationwide, 15.7% of cases were BA.4 and 36.6% were BA.5, according to data from the Centers for Disease Control and Prevention.
As of the week before, the BA.2.12.1 lineage of omicron was still the dominant strain of COVID in the U.S., and was responsible for an estimated 56% of cases. At the time, BA.5 made up an estimated 23.5% of cases.
According to the New England Journal of Medicine, studies have shown that "the levels of neutralizing antibodies" that previous infection or vaccinations create in the body are less effective against the BA.4 and BA.5 subvariants, but still provide “substantial protection” against severe illness.
The research could indicate that BA.4 and BA.5 could cause increased infections among all populations, including those who have been vaccinated and boosted, but also indicates that those vaccinations will still help to guard against severe illness.
According to officials in Europe, the BA.4 and BA.5 subvariants will likely become the dominant strains of the virus in coming weeks, and those sublineages have already been the dominant strains in South Africa, researchers told CNN.