Sharp increase in Mass. COVID-19 cases likely does not include expected Thanksgiving surge

People waited in line for a COVID-19 test in Lynn on Thursday.Pat Greenhouse/Globe Staff

Massachusetts on Wednesday reported a record number of new COVID-19 cases, but experts warn that the worst is yet to come.

Of the 4,613 cases reported, many are likely unrelated to Thanksgiving travel and gatherings, epidemiologists said. Since it can take up to 14 days for a person to test positive for COVID-19 after exposure — and sometimes far longer for an infected person to become seriously ill — current data do not yet reflect the expected post-holiday wave of new cases, hospitalizations, and deaths, they said.

“It’s only been seven days [since Thanksgiving], and we have an additional week from now to start seeing all of the cases of COVID-19 from the holiday, so it is very concerning that we’re already seeing a record number of cases,” said Dr. Jose Figueroa, an assistant professor at Harvard Medical School and Harvard T.H. Chan School of Public Health. “It suggests that things are only going to get worse.”

COVID-19 cases have been on the rise in Massachusetts throughout the fall. The 7-day average of new confirmed cases first surpassed 2,000 per day in early November, reports from the Department of Public Health show. Counts have exceeded 3,000 cases on several days in the past month.

Because transmission in the state was already accelerating ahead of the holidays, it is and will remain difficult to tease out the various factors behind this week’s sharp increase in cases, said Dr. Barry Bloom, a professor and former dean of the Chan School of Public Health.

“It’s all in the context of things going up even before Thanksgiving. That’s the dilemma,“ he said. “It’s hard to see an increase on top of an increase.”

Case counts over the next two weeks will better reflect the holiday’s impact on the steepness of the state’s upward curve, Bloom said. But he warned that even then, it will be difficult to say exactly where or how individual people were infected, given the high level of community spread.

“The best measure for the severity, which we’re already seeing going up — even independent of whatever happened over Thanksgiving — is hospitalizations,” Bloom said.

The state reported 68 new hospitalizations on Wednesday, bringing the total number of COVID-19 patients in hospitals to 1,259, and 46 new deaths.

Unlike case counts, these metrics do not depend on how many people get tested, or the relative risk of those tested compared with the state overall. But certainty comes with a downside: These indicators lag well behind a surge.

“The scary part is that we are not seeing the hospitalizations and deaths related to the Thanksgiving holiday season yet,” said Figueroa, who is a practicing physician at Brigham and Women’s Hospital. It could be up to five weeks from now before people who were infected during travel or family gatherings reach the point of critical illness, he said.

Figueroa said there is a light at the end of the tunnel, with multiple vaccines likely to become available in the coming months, and possibly before the end of the year. But he said that already high levels of community spread accelerated by back-to-back holidays paint a concerning picture of the weeks ahead.

The same factors that led people to flout public health guidance over Thanksgiving will be at play over the winter holidays, he said — desire to see family, cold weather driving people to gather indoors, exhaustion with pandemic rules.

“We still have another big holiday coming up,” Figueroa said. “We just got a big hit, and we’re about to go into another round with Christmas.”