Two Omicron subvariants gain ground in U.S. amid warnings of summer surge

June 8 (UPI) -- The Centers for Disease Control and Prevention is tracking two new, highly contagious Omicron subvariants that now account for almost 13% of all new COVID-19 cases in the United States.

Subvariants BA.4 and BA.5 made up 5.4% and 7.6%, respectively, of new COVID-19 cases between May 29 and June 4, according to new data published Tuesday by the CDC.

The sub-variants are even more prevalent in the West and the South, accounting for as much as 20% of new cases. The region with the highest proportion of BA.4 and BA.5 is Arkansas, Louisiana, New Mexico, Oklahoma and Texas with over 22% of new cases last week, according to the CDC.

The Omicron variant of COVID-19 has been dominant in the United States since Omicron overtook the Delta variant in last winter's surge. The country is experiencing its fourth-highest surge of COVID-19 cases since many regions dropped mask mandates and other pandemic protections.

"For the summer, going into the winter, I expect these viruses to be out there at relatively high levels," said Dr. Alex Greninger, assistant director of the University of Washington's clinical virology laboratory.

"Just the number of cases, the sheer disruptions of the workforce -- it's just a very high, high burden of disease."

Scientists warn the new Omicron subvariants are more contagious forms of COVID-19 that could cause breakthrough infections, despite vaccinations and immunity from past infections. But researchers are not sure if the infections are more severe or could lead to more hospitalizations or death.

Most new cases are still caused by the Omicron subvariant BA2.12.1, but some experts believe the newer subvariants could overtake it.

"Given the data we've seen so far, I'd expect BA.4 and BA.5 would continue to replace BA.2.12.1," said Dr. Tom Inglesby, director of The Johns Hopkins Center for Health Security.

Both BA.4 and BA.5 already have spread rapidly in other parts of the world. In May, the World Health Organization blamed the new subvariants for rising cases in more than 50 countries.

Both were first detected in South Africa, where they are currently dominant. And Portugal reported 26,848 new cases and 47 COVID-19 deaths last week, the highest since February, according to the European Center for Disease Prevention and Control.

Moderna announced Wednesday that its updated COVID-19 booster shot, not yet approved for use, produces a stronger immune response to the Omicron variant than its original booster.

Moderna said it still is gathering evidence on how its updated vaccine works against BA.4 and BA.5.