In just one week, another 150 vaccinated people tested positive for coronavirus in Massachusetts, according to the latest state data, bringing the total breakthrough cases to nearly 4,000 to date.
The so-called breakthrough cases — cases where fully vaccinated individuals test positive for coronavirus — have so far been rare, but are possible. The numbers account for approximately one in 1,000 vaccinated people in Massachusetts.
As of June 12, there were 3,791 cases of COVID-19 among more than 3.7 million fully vaccinated people in Massachusetts, according to the Department of Public Health. That's 150 more than the 3,641 breakthrough cases that were reported as of June 5, and 708 more than the 3,083 fully vaccinated people who had tested positive as of May 17.
According to the U.S. Centers for Disease Control and Prevention, a total of 10,262 breakthrough infections were reported throughout the country as of April 30, at which time 101 million people had been vaccinated.
More cases have likely gone unreported, federal officials have said, because they only have data from 46 states and territories. Additionally, most vaccinated people don't show symptoms that are serious enough to get tested.
Health experts are urging vaccinated people to get tested for coronavirus, even for the most mild symptoms, both to keep track of the virus and potential mutations as well as prevent further spread.
"Testing to identify current infection remains critical to control of COVID-19," a spokeswoman for the Department of Public Health said in a statement. "People with current infection can spread the virus to others and isolation of cases and identification of close contacts (individuals who may have been exposed) is a foundation of public health response."
In fact, the more contagious Delta COVID-19 variant, first identified in India, has been in Massachusetts for weeks now and is steadily rising. Experts say the Delta variant is more contagious and may be associated with a higher risk of hospitalization than the original "wild type" COVID-19 strain.
The number of COVID-19 cases in Massachusetts is low right now. Massachusetts health officials reported 55 new coronavirus cases and another two deaths on Tuesday as the state notched its four millionth vaccination and the number of estimated active cases fell below 2,500.
"It is important to continue to take appropriate public health action to keep that number low," the state health department spokeswoman said. "The public health recommendation encouraging testing remains in place as we continue to move through this pandemic to monitor for changes in COVID-19 activity."
The CDC stopped counting breakthrough infections last month. Instead, federal health officials are only tracking vaccinated patients who end up in the hospital or those who die from COVID-19.