The CDC estimates that two Omicron subvariants experts have been watching closely now account for more than 7 percent of New England COVID-19 cases.
The BA.4 subvariant accounts for 4.4 percent of cases, while the BA.5 subvariant accounts for 2.8 percent, the public health agency estimates.
Nationally, BA.4 accounts for 5.4 percent of cases, while BA.5 accounts for an estimated 7.6 percent, according to the CDC estimates.
The subvariants BA.2.12.1 and BA.2 still account for many more cases both nationally and in New England. In New England, BA.2.12.1 accounts for 64.5 percent of cases and BA.2 accounts for 28.3 percent of cases.
But experts say the new subvariants, first identified in South Africa, could end up elbowing out BA.2.12.1 and BA.2, just as those two variants elbowed out the BA.1 subvariant before them.
“We are probably past the peak of the BA.2.12.1 wave,” said Dr. Jacob Lemieux, an infectious disease specialist at Massachusetts General Hospital, who is also coleader of the viral variants program at the Massachusetts Consortium on Pathogen Readiness. “We’re at the beginning of seeing the impact of BA.4 and 5, which are the South African variants . . . and we do think they’re more transmissible and likely going to cause some surge in cases or, at least, that’s a real possibility.”
He said over the next few weeks, until around July 4, he expected “fairly sustained transmission” that would hopefully get a little better as the BA.2.12.1 wave passes but that could get “a little bit worse” as BA.4 and BA.5 account for more cases. “We’re going to be seeing a lot of ongoing acute COVID likely into the summer,” he said, “and there may even be a resurgence in the fall and winter.”
He also cautioned, “We don’t know what comes after BA.4 or 5. I think if there’s nothing from left field, we’ll have a reprieve. But I reserve the right to modify that forecast if we have BA.6 that we’re dealing with.”
Andrew Lover, an assistant professor of epidemiology in the School of Public Health and Health Sciences at the University of Massachusetts Amherst, said the experience of South Africa was worrisome.
“Unfortunately, South Africa saw a large surge of BA.4/BA.5 following extensive prior infections. We need to assume we’ll see similar trends here in Massachusetts, especially as many people’s vaccines and boosters start to wane. The good news is that vaccines are still providing good protection from hospitalizations and severe outcomes,” he said in an e-mail.
Matthew Fox, a professor of epidemiology and global health at the Boston University School of Public Health, said in an e-mail people should remain vigilant. “We still expect the vaccines and prior infection immunity to be pretty protective against severe illness, so at this point, we should just keep watch and prepare to make changes if needed.”
Dr. David Ho, a professor of microbiology and immunology at Columbia University in New York City, told CNN in an e-mail the new variants are “a serious threat.” Research by Ho and colleagues suggests BA.4 and BA.5 are more likely to lead to breakthrough infections, even in people who’ve had COVID-19 before, CNN reported.
Without upgraded vaccines or boosters, Ho told CNN, many people will get sick in the coming weeks to months. But he also said the new wave of infections would not necessarily bring more severe disease or deaths.
Jeffrey Shaman, an infectious disease modeler and public health researcher at Columbia University, told The New York Times last week the findings aligned with a growing body of evidence that the coronavirus has become more adept at reinfecting people and that outbreaks are likely to continue.
“We have to admit the possibility that the number of waves that we’ve seen over the past few years, it may continue at that cadence,” Shaman said.
Material from Globe wire services was used in this report.
Martin Finucane can be reached at firstname.lastname@example.org.