Mass. reports 4,378 new breakthrough cases for the last week

There have been another 37 deaths among vaccinated individuals.

The number of new breakthrough cases of COVID-19 in vaccinated individuals this week was slightly lower than last week, but thousands across Massachusetts are still reporting breakthrough infections. 

The state released updated data Tuesday on the number of COVID-19 cases, hospitalizations, and deaths among vaccinated individuals in Massachusetts. There have been a total of 36,723 breakthrough cases of COVID-19 as of Sept. 25, an increase of 4,378 from Sept. 18. Between Sept. 11 and Sept. 18, 4,568 breakthrough cases were reported, so 190 fewer breakthrough cases were reported this week.

There were 4,610,534 people vaccinated as of Sept. 15, meaning 0.80% reported a breakthrough case of COVID-19. The rate has been steadily increasing — it was 0.23% on Aug. 7. 

However, another way to understand the prevalence of breakthrough cases is by comparing how many of the total number of newly reported COVID-19 cases are breakthrough infections.


Between Sept. 19 and Sept. 25, 10,446 people tested positive for COVID-19, and 4,378 breakthrough cases were reported. So, 41.9% of COVID-19 cases in that period were breakthrough cases. The week before that, 39.4% of COVID-19 cases were breakthrough infections.

Again and again, health officials like Dr. Ashish Jha and Dr. Anthony Fauci have said breakthrough infections do not mean a vaccine is failing. An August blog post from MIT Medical warned people to expect that “in places with high vaccination rates, vaccinated people will constitute a high percentage of new cases.”

“Among UNvaccinated, about 1 in 20 infections lead to hospitalization and 1 in 200 lead to death,” Jha wrote on Twitter Sept. 14. “Vaccines cut risk of each by 90%.”

Hospitalizations and deaths are also increasing but at a much lower rate. Tuesday’s data showed a total of 1,155 hospitalizations and 254 deaths, an increase of 154 and 37 respectively from Sept. 18. So, out of vaccinated individuals, 0.03% have been hospitalized and 0.006% have died. According to the data, 3.14% of breakthrough cases resulted in hospitalization and 0.69% resulted in death.

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