The omicron subvariants BA.4 and BA.5 are spreading rapidly in the United States, but it's not yet clear if they'll trigger a new wave of infections or a surge in hospitalizations and deaths, experts say.
The subvariants now account for 13% of new coronavirus cases nationwide, compared with 7.5% a week ago and 1% in early May, according to new estimates released Tuesday by the Centers for Disease Control and Prevention.
That suggests that BA.4 and BA.5 could outcompete two other omicron subvariants, BA.2 and BA.2.12.1, which together account for most cases at the moment, according to Denis Nash, epidemiologist, CUNY Graduate School of Public Health & Health Policy.
"This could happen very quickly," Nash told the The New York Times.
The subvariants have become common in parts of the southern United States. In the region comprising Arkansas, Louisiana, New Mexico, Oklahoma and Texas, BA.4 and BA.5 account for more than 1 in 5 infections, the Times reported.
Despite widespread immunity to the coronavirus, South Africa experienced a surge of cases in April and May that were fueled by BA.4 and BA.5.
However, that wave was not as large as previous ones and deaths did not increase as steeply, Jeffrey Shaman, an infectious disease epidemiologist at Columbia University in New York City, told the Times.
"How analogous is that for us?" he said. "I think it's possible that we could see another wave" fueled by BA.4 and BA.5.
But, if the United States echoes South Africa's surge -- which is not certain -- the wave might be more modest than previous ones and cause smaller increases in hospitalizations and deaths, Nash suggested.
Over the last few weeks, the United States has averaged about 100,000 new coronavirus cases a day, compared with less than 30,000 in late March, a Times database shows.
COVID-19 hospitalizations have started to fall in the Northeast, but are increasing elsewhere. Deaths have been between 250 and 400 a day over the last month, which is much lower than during the winter Omicron surge, the Times reported.