Nearly 400 people have been hospitalized and 100 have now died in Massachusetts due to COVID-19 breakthrough cases after they were fully vaccinated, state health officials said this week.
What is a breakthrough COVID case, how common are they, and how are they being tracked? Here's what you should know.
What is a breakthrough COVID case?
A vaccine breakthrough case occurs when a person tests positive for COVID-19 after they've been fully vaccinated against the disease.
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A person is considered “fully vaccinated” two weeks after receiving the second dose of either the Pfizer or Moderna COVID vaccine, or two weeks after receiving the single-dose Johnson & Johnson vaccine.
How many breakthrough COVID cases has Massachusetts had?
Public health officials have tracked 7,737 "breakthrough" cases of COVID-19 among Massachusetts residents fully vaccinated against the disease, representing 0.18% of the roughly 4.3 million people immunized.
About 95% of the infections in vaccinated residents did not require hospitalizations, while 395 people, or 5.1%, were hospitalized, according to state Department of Public Health data through July 31.
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 going forward.
One hundred vaccinated residents in Massachusetts died from COVID-19, either without being hospitalized or following a hospital stay, DPH said. That death toll reflects 1.2% of the 7,737 confirmed breakthrough cases and 0.002% of the 4.3 million people fully vaccinated as of July 31.
Tufts Medical Center Epidemiologist Dr. Shira Doron told NBC10 Boston this week that while breakthrough cases are troubling, 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," she said.
How many total breakthrough deaths have been reported in the US?
The CDC transitioned from monitoring all reported breakthrough cases to only reporting hospitalizations or deaths on May 1, the agency said.
As of July 26, the CDC said it received reports from 49 U.S. states and territories of 6,239 patients with COVID breakthrough infection who were hospitalized and 1,263 who died. About 52% of those patients were male and 48% female. Seventy-four percent were 65 or older.
Even though the total number of breakthrough cases at this point is not made publicly available, federal health officials did track all breakthrough cases from January of this year through April 30, 2021.
The CDC said that in that time period, a total of 10,262 breakthrough COVID cases were reported in 46 U.S. states and territories. About 63% of those cases were in women, with the median patient age at 58 years.
The CDC said 27% of those breakthrough infections were asymptomatic, while 2% died.
About 10% of those breakthrough cases were hospitalized, officials said, but among those hospitalized, 29% were asymptomatic or hospitalized for a reason other than COVID-19.
How common are breakthrough COVID cases?
While breakthrough cases have been considered rare, they are possible and even "expected," per the CDC. Experts have said that while the vaccine itself cannot give you the virus, it is also not 100% effective at preventing the virus entirely, though those who receive the vaccine are far less likely to be hospitalized or die from it, data shows.
"COVID-19 vaccines are effective and are a critical tool to bring the pandemic under control," the CDC's website reads. "However, no vaccines are 100% effective at preventing illness in vaccinated people. There will be a small percentage of fully vaccinated people who still get sick, are hospitalized, or die from COVID-19."
The CDC says this is true of all vaccines: not one prevents illness 100% of the time.
Massachusetts health officials continue to urge those who have not gotten vaccinated yet to do so.