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Here’s who gets breakthrough COVID cases in Mass.

The Moderna COVID-19 vaccine.Angel Navarrete/Bloomberg

A substantial portion of the people who have suffered breakthrough COVID-19 hospitalizations and deaths in Massachusetts have been elderly or had underlying conditions, according to state data.

The Department of Public Health says that as of Aug. 31, there had been a cumulative total of 144 breakthrough case deaths in the state. The median age of those who died was 81.2 years, meaning half the deaths were among people above that age and half were below. The DPH also said that in 73 percent of the deaths the patients had underlying medical conditions.

The DPH reported a cumulative total of 651 breakthrough case hospitalizations. The median age of those hospitalized was 71.1 years. The DPH also said that in 54 percent of those hospitalizations the patients had underlying conditions.


Massachusetts officials have emphasized that the state is a national leader in vaccinations and say that, as a result, the number of breakthrough cases is “incredibly low” and breakthrough hospitalizations and deaths are “even lower.”

The Department of Public Health says that the cumulative total of breakthrough deaths and hospitalizations accounted for 0.003 percent and 0.01 percent, respectively, of the 4.5 million individuals fully vaccinated as of Aug. 31.

“With a very small fraction of one percent of all vaccinated people being hospitalized, the data is clear that vaccines are the best way that residents can protect themselves and their families from the virus,” an Executive Office of Health and Human Services spokesperson said in a statement.

“More of our population is vaccinated than almost any other state. With more of our residents protected, fewer are getting very sick than almost anywhere else,” Governor Charlie Baker said in a series of tweets on Aug. 29.

“The facts are clear: Vaccines are working. ... Getting the vaccine is the best way to protect yourself and your loved ones,” he said.


The state data bore some similarities to a recent preprint study from a US Centers for Disease Control and Prevention researcher that looked at data from a hospitalization surveillance network of US acute care hospitals. The study found that fully vaccinated people admitted to the hospital tended to be older (with a median age of 73) and were more likely to have three or more underlying medical conditions and live in long-term care facilities.

The study went further, finding that unvaccinated adults were roughly 17 times more likely to be hospitalized with severe COVID-19 than vaccinated adults from Jan. 1 to July 24. It joins other studies that have also found the vaccines are highly protective against hospitalizations.

Older people and those with underlying conditions have been at higher risk since the beginning of the pandemic and that appears to continue even among the vaccinated, said Dr. David Hamer, an infectious disease physician at Boston Medical Center and professor at Boston University. He said the DPH data underlined the need for people in those groups to to take precautions.

“Everyone should be careful, but, in particular, very vulnerable members of our population — they need to be super cautious right now until this current wave dies down,” he said.

“Anybody who fits these demographics needs to be really careful if they’re going to be in any public place where they might be exposed to someone with COVID-19,” he said.


Dr. Howard Koh, a former high-ranking US and state public health official who is now a professor at the Harvard T.H. Chan School of Public Health, said in an e-mail, “These data reconfirm that the elderly with underlying conditions, especially those in nursing home settings, rank among the most vulnerable of all vulnerable groups. Extra care and vigilance for them -- and their caregivers -- should remain a priority for policymakers and the general public alike.”

Hamer said it may be time to give booster shots to people in the vulnerable groups because they may not have responded robustly to the first set of shots and because they received their shots earlier and the protection might be waning.

The government has already recommended third shots for immunocompromised people and the Biden administration says it wants to administer booster shots to everyone as soon as such shots get federal approval.

Matthew P. Fox, a professor in the epidemiology and global health departments at Boston University, said he wanted to see well-designed, careful epidemiological studies of the vaccine’s impact, not just raw data from the state, but the evidence still suggests the vaccine is “working very well.”

“Seeing low numbers of deaths and hospitalizations in the vaccinated is a good sign,” he said.

“We will also need to see if things change over time as we know less about how people will be affected by the Delta variant,” he said.

He cautioned that “those who were younger and healthier were always at less risk, so they are likely to have a better response to the vaccine. But breakthrough cases will still happen in this group.”


The number of breakthrough cases, hospitalizations, and deaths is likely to continue going up, he said, because so many people in the state are vaccinated. “The hope,” he said, “is that this number will be well below what it would have been had people not been vaccinated.”

Jonathan Saltzman of the Globe staff contributed to this report.

Martin Finucane can be reached at martin.finucane@globe.com.