The delta variant of COVID-19 is fueling a summer surge in infections.
Nearly 8,000 fully vaccinated Massachusetts residents have now tested positive for COVID-19 and 100 of them have died, according to state data on breakthrough cases published Tuesday.
The Department of Public Health tracked a cumulative 7,737 confirmed COVID-19 infections among those fully vaccinated in the state as of July 31, representing 0.18% of the immunized population.
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The 100 deaths out of nearly 4.3 million vaccinated residents represents a rate of just 0.002%.
Saturday's cumulative count reflects an increase of 1,364 breakthrough cases over July 24. That accounts for a bit more than 30% of all new coronavirus cases confirmed in the state during that one-week span.
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Since the first residents became fully vaccinated in January, DPH has counted 395 immunized residents hospitalized with COVID-19 cases and 100 who died from the virus. Those numbers include 34 new breakthrough hospitalizations and nine additional deaths among those fully vaccinated tracked in the past week.
Overall case numbers have been on the rise in Massachusetts and nationwide for weeks as the more infectious delta variant spreads, including among those who are fully vaccinated, but health experts have repeatedly stressed that vaccinations reduce the risk of serious injury or death in the rare breakthrough cases.
Health officials reported another 883 confirmed coronavirus cases -- the most in a single day since early May -- and two new deaths on Tuesday, while the positive test rate rose above 2.5%.
The report pushed the state's confirmed COVID-19 caseload to 675,425 since the start of the pandemic and its death toll to 17,718. The last time more than 883 COVID cases were reported in one day was on May 6.
Tufts Medical Center Epidemiologist Dr. Shira Doron says public health experts still have a lot to learn about COVID-19.
"The models have gone out the window, the mathematical models, in terms of where things are heading, no longer help us predict anything," she said.
Doron says while breakthrough cases are concerning, they're not as concerning as the need for vaccinations worldwide.
"We do need to put some of these numbers in a more realistic context just so people – you know, so people don't panic, so people make the right decisions based on the actual risk," Doron said.
Officials say most new cases, and especially serious infections, are in the unvaccinated.
"Before delta, we had hoped that we had seen kind of the worst of what the virus could do in terms of mutation," Doron said.
Now, with the "delta plus" variant detected in smaller numbers, she says looking at this pandemic globally is more important than ever.
"When we allow it to rage uncontrolled in other parts of the world and don't get vaccine to them, the virus will keep mutating," she said.
DPH previously released data on breakthrough infections in response to records requests, and on Tuesday it published those figures for the first time as part of the vaccination report it releases every weekday.
The department said it plans to continue including updated breakthrough numbers in Tuesday vaccination reports.
