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8 things to know about the Omicron BA.2 variant

A drive-though COVID-19 testing site in Hagerstown, Md.Kenny Holston/NYT

With COVID-19 cases rising again in both Europe and Asia, experts and officials are keeping a close watch on the Omicron subvariant BA.2 in the United States. They’re worried cases will increase here, too, just as the country has been enjoying a desperately needed reprieve from the two-year-long pandemic.

“I know the public is done with the virus, but the virus isn’t done with us,” Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told Politico.

Here’s what you need to know about the variant:

BA.2 is believed to be a more contagious version of the Omicron variant


There are several different varieties of the Omicron variant. BA.2 is believed to be even more contagious than BA.1, the variety that swept through the country this winter, causing a devastating surge in cases, hospitalizations, and deaths. “BA. 2 is more transmissible, and this is the most transmissible variant we have seen of the SARS-COV2 virus to date,” Dr. Maria Van Kerkhove, COVID-19 technical lead at the World Health Organization, said in a media briefing Wednesday.

The proportion of US cases caused by the BA.2 variant is rising swiftly

According to the latest estimates from the US Centers for Disease Control and Prevention, BA.2 accounts for about 23.1 percent of COVID-19 cases nationally. That number was up from less than 1 percent in late January. In New England, the CDC estimates, the current proportion of BA.2 cases is even higher, 38.6 percent, in the week ending March 12.

BA.2 appears to have the same severity as other varieties of Omicron

BA.2 appears to cause illness of the same average severity as BA.1, which was less severe than the Delta variant. The problem is that a greater level of infectiousness means many more people can catch the disease, some of whom will become severely ill. “We do not see an increase in severity with BA.2. However, with huge numbers of cases you will see an increase in hospitalizations, and we have seen this in country after country,” Van Kerkhove said.


Vaccines appear to work against BA.2

BA.1 was able to evade some of the protection offered by vaccines, which led to breakthrough infections during the winter surge. But the vaccines continued to offer protection against severe disease. The same appears to hold true for vaccine protection against BA.2. British health officials have found little difference in the effect of vaccines against BA.1 and BA.2 infections.

Some treatments don’t work against it

Most monoclonal antibody treatments don’t work for either BA.1 or BA.2. Some treatments, such as Evusheld, do work. The antiviral drugs paxlovid, molnupiravir, and remdesivir are all still highly effective.

People who have had Omicron are protected

Having a previous Omicron infection offers protection against getting a BA.2 infection. That’s good news for the United States because a large number of people were infected during the winter surge. And that number adds to the large number of Americans who have gotten vaccinated and boosted.

But there’s concern about waning immunity

But there are concerns that that immunity may weaken. One of the possible drivers of the BA.2 increases in European countries, experts say, is immunity waning from vaccines or prior infections. They worry that BA.2 could arrive here in force just as that happens here. Another possible driver: the lifting of pandemic restrictions, which has also happened in the United States.


The virus has surprised us before

The worries about COVID-19 surges in other countries are being raised as pandemic numbers have dropped in the United States, as well as in Massachusetts. But the unpredictable virus has caught people by surprise before, and now is not the time to let our guards down, experts said.

“We are breathing easier,” Ezekiel Emanuel, vice provost for global initiatives at the University of Pennsylvania and former member of the Biden transition team’s COVID-19 advisory board, told reporters Wednesday. “The mortality rate is coming down, the case rate is coming down, hospitalizations are coming down. But let’s remember, we’ve been here before.”

Martin Finucane can be reached at martin.finucane@globe.com.