Reports of 'Breakthrough' COVID Cases After Vaccine

Carolyn Crist

March 08, 2021

A small number of people have tested positive for COVID-19 more than two weeks after being fully vaccinated, which is also known as a "breakthrough" case.

The two-week mark is important because the body needs enough time to develop immunity, according to Prevention. So far, those with breakthrough cases have reported mild or no symptoms.

Earlier this week, the Minnesota Department of Health announced that it was investigating several of these cases across the state. The department issued an advisory that asked hospitals, clinics, urgent care centers and emergency departments to report any cases where people test positive for COVID-19 at least 14 days after completing their second vaccine dose.

"These vaccines that we're using are fabulous but they're not perfect," William Schaffner, MD, an infectious disease specialist at Vanderbilt University School of Medicine, told Prevention.

"At best, they're 95% effective in preventing serious illness, but minor illnesses can occur," he said.

Although researchers expect that some breakthrough cases may occur, they're primarily focused on whether patients develop symptoms. Among 14 breakthrough cases identified in Minnesota, all were health care workers who tested positive during routine screening for work. All reported mild or no symptoms.

"The [Pfizer] vaccine is 95% effective, that means that theoretically of 100 people vaccinated, there may be five who don't have the same level of response to provide protection," Kris Ehresmann, director of the infectious disease division at the Minnesota Department of Health, told CBSN Minnesota.

Oregon has also reported a handful of breakthrough cases, according to an Oregon Health Authority statement posted on Facebook. Four cases had been identified by mid-February, and all had mild or no symptoms.

"Such cases are not unexpected," according to the statement. "Clinical trials of both vaccines presently in use included breakthrough cases."

Even so, vaccines reduced the severity of illness, the statement said. The same types of breakthrough cases happen with other diseases and vaccines as well, such as the flu.

Breakthrough cases provide a reminder for people to continue to take precautions against the coronavirus as they get vaccinations this year, CBS Minnesota reported.

"You still need to mask, you still need to make sure you're socially distancing and consider those mitigation guidelines measures that we've been talking about for the last year," Ehresmann


Prevention, "Some States Are Reporting 'Breakthrough' Cases of COVID-19—Here's What That Means."

Minnesota Department of Health, "Health Advisory: COVID-19 Vaccine Breakthrough Cases."

CBSN Minnesota, "MDH Tracking 14 COVID 'Vaccine Breakthrough Cases'; All Had Mild Or No Symptoms."

Oregon Health Authority, "Breakthrough Cases, Facebook post on Feb. 12, 2021."