Experts: Memorial Day might bump up cases, but it’s less likely in states like Mass. with high vaccination levels

People traveled and gathered for the Memorial Day weekend, but the vaccines are expected to hold the coronavirus in check - particularly in well-vaccinated areas like New England.Craig F. Walker/Globe Staff

Keep your eye on the numbers. Experts say it’s possible there will be a coronavirus case increase because of people traveling and gathering over the Memorial Day weekend, but it’s less likely to be a problem in places with higher vaccination rates like Massachusetts and other New England states.

“We’re right in the middle of the incubation period,” said Dr. David Hamer, a physician at Boston Medical Center and a Boston University epidemiologist, “I think the next few days will be key.”

But he also said, “I suspect we’ll be fine in Massachusetts and New England, with a very low likelihood of seeing a post-Memorial Day spike. I am more concerned about other parts of the country,” where fewer people have been vaccinated.

Dr. Philip Landrigan, an epidemiologist and director of the Program for Global Public Health and the Common Good at Boston College, said that the potential impact of the holiday wouldn’t be known until 14 to 21 days after the weekend.

He said the chances of a spike in Massachusetts were “relatively low” and “if we see an uptick, it’s going to be a bump and not a spike.”

If the deadline passes without any spike nationally, he said, it will signal “that the national vaccination strategy that President Biden has championed is working.”

Dr. Prathit Kulkarni, assistant professor of medicine in infectious diseases at Baylor College of Medicine in Houston, said, “If there is to be a spike after Memorial Day, I would expect it over approximately the next 7-10 days. However, this is much less likely in areas where larger proportions of the population are vaccinated. So the key is continued strong vaccination, which can mitigate these kinds of potential spikes.”

“It remains the case that large groups of unvaccinated people meeting without precautions can potentially lead to localized clusters and outbreaks,” he cautioned in an e-mail.

Michael Mina, an epidemiology professor at the Harvard T.H. Chan School of Public Health, said he didn’t expect much of a spike. He said there might be “a very low bump upwards in cases, but particularly because it is an outside-centric holiday, I’m not too concerned.”

Mina said in an e-mail he only expected “potential small bumps here and there through summer and early fall,” though he warned there may be increases ahead later in the fall.

Dr. Chris Beyrer, a professor of epidemiology, nursing, and medicine at the Johns Hopkins Bloomberg School of Public Health, said for the moment “US trends are truly heartening” but he was concerned about immunization rates “varying significantly” among states and among ethnic and religious minorities.

“We need better national coverage,” he said in an e-mail, both to save lives and “reduce the very real risk that new variants of concern could emerge in unvaccinated populations which might undermine our current generation of effective vaccines.”

Nationally, 62.9 percent of adults have gotten at least a first dose of vaccine, and President Biden on Wednesday announced a “month of action” to urge more Americans to get vaccinated before the Fourth of July holiday.

Massachusetts is a national vaccination leader, with 78.8 percent of adults given at least a first dose, according to data from the US Centers for Disease Control and Prevention. Other New England states are also among the top performers. Meanwhile, some states are lagging significantly. The lowest percentages are mostly in the South, with Mississippi coming in last at 44.1 percent.

Massachusetts Governor Charlie Baker at a Wednesday news conference noted the dramatic decline in coronavirus numbers since the peak of the second surge early this year and cited the impact of vaccinations. “Here in Massachusetts we have watched week over week over the course of the past five months, as the more people got vaccinated ... the fewer people got sick, the fewer people got hospitalized, and the fewer people passed away,” he said.

Baker lifted many of the state’s coronavirus restrictions as of Saturday, the first day of the holiday weekend.

Last week, CDC Director Rochelle Walensky noted that the nation was in a new position: entering a holiday weekend with a substantial number of vaccinations administered. She said vaccinated people could enjoy the weekend, but she also warned unvaccinated people they still needed to wear masks and take precautions.

Dr. Howard Koh, a professor at the Harvard T.H. Chan School of Public Health and a former high-level federal health official and Massachusetts public health commissioner, said he was “hopeful that a post-holiday bounce is not likely — given the rising levels of protection already achieved through vaccination and post-infection immunity.” But he added, “We always need to stay vigilant.”