Dr. Sandro Galea, an epidemiologist and dean at the Boston University School of Public Health, thinks it's too soon to draw a storyline about what's driving Massachusetts' rebound.
"There's enormous patchiness," he said of the state's outbreak, which looks very different in Boston than it does in rural areas in western Massachusetts.
And while there's evidence that people under the age of 30 are driving the rebound in new cases this fall, Galea doesn't think the rise is related to Boston's high density of universities, some of which have opened in person.
"Transmissions are quite low," he said of schools.
Instead, he pointed to informal gatherings, especially among young people. "Whether those can come under control is an open question," Galea said. "It's fluctuating day by day."