COVID-19 cases rising in Northeast, partly fueled by BA.2, experts say

As COVID-19 cases continue to tick up in the United States, the Northeast appears to be fueling the increase.

Four of the five states with the highest seven-day case rates per 100,000 are in the Northeast. In the 10 states with the highest seven-day rates, seven are Northeastern, according to data from the Centers for Disease Control and Prevention.

Rhode Island currently has the highest seven-day case rate at 172.4 cases per 100,000 people. This is nearly three times higher than the national rate of 59.4 cases per 100,000 people.

As of Friday, the Ocean State has also seen its average daily number of cases increase 53% over a two-week period from 170 per day to 260 per day, CDC data shows.

Other Northeastern states seeing increases include Vermont, New York, New Jersey, Maine and Connecticut.

In particular, New York and New Jersey have seen their average daily cases increase by 64%, the CDC data shows.

Experts said one of the reasons for the rise in cases is the spread of BA.2, a subvariant of the original omicron variant that is more transmissible.

In the Northeast, BA.2 accounts for more than 84% of COVID-19 cases that have undergone genomic sequencing, more than any other region in the country, according to the CDC.

Dr. Ali Mokdad, an epidemiologist with the University of Washington's Institute for Health Metrics and Evaluation, told ABC News that early evidence suggests people who were infected with the original omicron variant during the previous wave may now have some immunity against BA.2.

He suggested states that were able to have better control of cases earlier may currently be more vulnerable to infections.

"States that did a good job controlling infections with mandates, most in the Northeast and West, are more susceptible now with BA.2," he said.

Mokdad compared Maine and Florida using data from the institute, which projects COVID-19 cases around the country.

"We estimate that 54% of people in Maine have been infected at least once as of April 4," he said. "So, we estimate that 60% are immune. We estimate that 87% of people in Florida have been infected at least once as of April 4. We estimate that 80% are immune."

Another reason Northeastern states may be seeing case increases is due to the lifting of mask and vaccine requirements, the experts said.

"Not only is BA.2 extraordinarily transmissible, but now, consistent with CDC guidelines, many people are going to crowded indoor events and outdoor events without wearing a mask and not social distancing," Dr. William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt University in Nashville, Tennessee, told ABC News. "In anticipation of summer ... people are eager to see family and friends and engage in near-normal activities again."

However, the experts warned the true number of cases could be even higher as some states shift their COVID-19 testing strategy.

In late February, the Rhode Island Department of Health announced that -- starting March 7 -- state-run testing sites would not accept asymptomatic patients unless they had been in close contact with a person who tested positive for the virus.

"Focusing testing efforts at Rhode Island's state-run testing sites on people who are symptomatic and people who are close contacts will ensure that people who are positive and eligible for treatment can be quickly connected to treatment," the department said in a news release.

Schaffner said he expects that the rise of cases in the Northeast will be followed in the next few weeks by increases in the Midwest, the South and the West.

"This is reminiscent of the very beginning of COVID here in the United States," he said. "The Northeast led the rest of the country; they had the most infections for quite a period of time before the COVID virus spread to the rest of the county. So perhaps this is a little bit of history repeating itself."

However, the doctors reiterated that unvaccinated people are at the highest risk of severe illness and death from BA.2 and stressed the importance of getting vaccinated and boosted.