New data Tuesday from the Centers for Disease Control and Prevention show omicron’s more transmissible BA.2 subvariant now accounts for more than a third of the virus circulating in the U.S. but is not yet driving a surge in cases here as it has overseas.
The CDC data show that as of March 19, BA.2 — often referred to as “stealth omicron” — accounted for 34.9% of genetically sequenced samples across the U.S., up from 22.3% as of March 12 and 12.6% on March 5. In the Northeast, BA.2 accounts for as much as 55.4% of the virus, and in Western states including California, 41.3%.
Dr. George Rutherford, a professor of epidemiology and biostatistics at the University of California-San Francisco, said the increase is “about what I expected” given the subvariant’s transmissibility.
“It will continue to climb at 10 percentage points a week or so,” Rutherford said.
With COVID cases overall on the decline in recent weeks, the bigger question is whether the highly contagious BA.2 subvariant will fuel another surge in the U.S.
Helix, a company that provides genetic sequencing of the virus, estimates that BA.2 accounts for as much as 70% of new cases in many parts of the U.S., the Washington Post reported Tuesday.
Basically, BA.2 is replacing omicron’s BA.1 but isn’t yet causing an increase in the total cases of COVID-19 or hospitalizations.
Dr. Eric Topol, director of the Scripps Research Translational Institute and a professor of molecular medicine at the Scripps Research Institute who has warned BA.2 could spark a new U.S. case surge, said Tuesday on Twitter that if BA.2 is as prevalent as Helix estimates and U.S. cases aren’t increasing overall, “it’s a very encouraging sign so far.”
“It’s surprising, not easily explained,” Topol tweeted Tuesday, “but gratifying to see — and hope it holds up.”
Ali H. Mokdad, a professor of health metrics sciences at the University of Washington’s Institute for Health Metrics and Evaluation, which runs a widely followed model projecting the pandemic’s course, said Tuesday on Twitter that his group isn’t projecting a significant new case spike.
“Our models suggest that behavioral modification, particularly declines in mask use and social distancing, may be the most important explanation for the increasing case numbers in some countries in Europe,” Mokdad continued. “However, it is possible that the rapid return to pre-COVID-19 behavior and the spread of BA.2 (in the U.S.) could see a short period of increasing case numbers.”
National health officials have urged caution.
“We likely will see an uptick in cases as we’ve seen in the European countries, particularly the U.K., where they’ve had the same situation as we’ve had now,” Dr. Anthony Fauci, the president’s chief medical advisor, said Sunday on ABC’s This Week. “They have the BA.2, they have a relaxation of some of the restrictions such as indoor masking, and there’s a waning of immunity.”
“Hopefully we won’t see a surge,” Fauci continued, adding that “we have to be prepared” and that it’s “no time at all to declare victory because this virus has fooled us before.”
Topol and other experts say BA.2 is about 30% more transmissible than BA.1, the omicron strain that drove this past winter’s massive case surge. A number of high-profile figures have tested positive for the virus in recent weeks, including former President Barack Obama, Vice President Kamala Harris’ husband Doug Emhoff, San Jose Rep. Zoe Lofgren and on Tuesday, White House Press Secretary Jen Psaki, who’s both vaccinated and recently infected, having tested positive in October.
Other counties have had more worrying experiences: The United Kingdom reported Tuesday that cases were up 20.4%, hospitalizations up 21.7% and deaths up 17.1% over the previous seven days.
But there also are indications that case spikes in some European countries hit by BA.2, such as the Netherlands, may have peaked.
Rutherford said that for those who are vaccinated and had booster shots if needed, they’ve done all they can to protect themselves. The vaccines continue to provide good protection against severe COVID-19, he said.
“It’s not more difficult to treat. It doesn’t cause more severe disease,” Rutherford said. “Keep your eyes on the prize, which is cutting down on hospitalizations, mortality, not disrupting schools, not disrupting businesses.”
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