Weekly Report Detects 2,200 More Breakthrough Cases

In the last week, 2,232 fully vaccinated people have tested positive for COVID-19 in Massachusetts, the Department of Public Health said Tuesday, representing more than one-third of all cases in that time based on the state's seven-day average of new cases.

DPH said Tuesday that there have been a cumulative 9,969 breakthrough infections reported out of 4,321,931 fully vaccinated people as of Aug. 7 -- meaning that 0.23 percent of all fully vaccinated people have subsequently been infected with the coronavirus, up from 0.18 percent of the immunized population a week ago.

A total of 445 people with breakthrough infections, or 0.01 percent of all vaccinated people, have been hospitalized and 106 fully vaccinated people, or 0.002 percent of people who have gotten vaccinated, have died of COVID-19, DPH said.

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With its update Tuesday, DPH cautioned that there are probably more breakthrough infections and hospitalizations among fully vaccinated people than it counts and can report.

The case count "may be undercounted due to discrepancies in the names and dates of birth of individuals, resulting in an inability to match records across systems," DPH said in a small text note and added that its hospitalization data "is likely also undercounted as identification and reporting of hospitalized cases relies on that information being obtainable by case investigators through patient interview."

When DPH first reported breakthrough case data as part of its Tuesday vaccination reports last week, it counted 7,737 such infections as of July 31. The 2,232 newly-reported breakthrough cases represent about 40 percent of the state's recent one-week total of new cases, based on the seven-day average of 780 new cases each day that DPH reported Monday.

The cluster of breakthrough infections that popped up after the July 4 holiday weekend among residents and visitors to Provincetown, in which about 75 percent of people who tested positive had been fully vaccinated, has been studied in detail by the U.S. Centers for Disease Control and served as a basis for that agency to update its masking guidance.

But Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, said Tuesday that he expects to hear about other breakthrough infection hotspots like Provincetown.

"I don't believe it's the only one because we're seeing similar findings in Israel and South Africa and other places in the world. So it is likely we will see more outbreaks in fully vaccinated individuals," he said during a virtual event hosted by the Massachusetts High Technology Council. "But so far, vaccines are still doing a very good job of keeping people out of the hospital and keeping people from dying, and that's really, I think, an incredible testament to how good the vaccines are in the setting of what is now a more deadly and a more fearsome foe, called the Delta variant, than what we had previously."

As the Delta variant continues to course through the population, Barouch and others on the MHTC panel said Tuesday that the fact that most people infected in Provincetown had minimal symptoms and did not develop severe cases of the disease is "the strongest reason ever for people to get vaccinated."

Massachusetts General Hospital President Dr. Peter Slavin said during Tuesday's MHTC event that doctors and nurses have gotten quite good at treating COVID-19 patients, though they are tired and frustrated that another surge of the virus is upon them. Despite the uptick in cases, he said things have not gotten hairy at the hospital again.

Before vaccines were widely available, the rate of new infections was closely linked to the increase in hospitalizations. But that's changed, Slavin said. There has been an 11-fold increase in cases since the start of the summer, but hospitalizations in Massachusetts have increased just three-fold, he said.

"So there's been a decoupling of the increase in cases from the increase in hospitalizations, and that I think is all due to vaccination," Slavin said.

Colin A. Young, State House News Service