By Louisa Moller

PROVINCETOWN (CBS) — A popular summer destination on Cape Cod is reporting some “breakthrough” COVID cases – meaning positive tests in those that have been fully vaccinated against the coronavirus.

Provincetown reported 20 to 25 positive COVID cases last week and “the majority were fully vaccinated” people, according to the Barnstable County Department of Health. Most have only experienced mild symptoms.

Those cases may not include individuals who left Massachusetts and tested positive in their home states, according to Barnstable County Public Health Nurse Deirdre Arvidson.

“Over half of those were people were short term visitors and have gone back home,” Arvidson said.

Provincetown is now asking the state for more COVID testing capacity.

“We are aware of a handful of positive COVID cases being reported over the last few days among folks who have spent time in Provincetown,” Town Manager Alex Morse said in a statement to WBZ-TV. “We are in touch with the Health Department and Outer Cape Health Services and are closely monitoring the data.”

Morse emphasized that “the vaccine works” and symptoms are less severe in those that have received shots. He said nearly all of the year-round and part-time residents of Provincetown are fully vaccinated.

South Boston man Travis Dagenais claims he is one of the individuals who is experiencing a breakthrough case. Dagenais says he started experiencing symptoms when he returned home and then received a positive test result.

“Probably the worst fever I’ve ever had in my life, probably the worst chills I’ve ever had and just complete exhaustion,” he said.

While experts say both the Pfizer and Moderna vaccines are more than 90 percent effective and preventing new COVID-19 infections, some doctors argue that these breakthrough cases highlight a glaring issue with data collection.

The CDC reported roughly 10,000 breakthrough cases among the more 157 million fully vaccinated Americans between January and April 30 of this year. Since then, the CDC stopped tracking mild breakthrough cases and only follows breakthrough cases that result in hospitalization or death.

“We still don’t have data on the breakthrough cases per state. We don’t have data on vaccination per breakthrough cases,” said Dr. Leo Nissola, an immunologist and medical advisor for the Covid Act Now Project.

Nissola argues that data on mild breakthrough cases could indicate whether contagious variants are impacting the effectiveness of the vaccines. It may also provide clues to how long immunity after vaccination lasts.

WBZ-TV’s Kristina Rex reports

“What we know for sure is that vaccines are safe, vaccines are effective, but we need to talk about breakthrough cases,” Nissola said.

CBS News reports that the Delta variant accounts for more than half of new COVID cases in the United States, and 99.7% of new cases are among people who have not been vaccinated.

Morse says travelers headed to Provincetown and those concerned about getting COVID should “make decisions that feel right for them.”

“We have a lot of visitors in Town, and given the volume, it’s inevitable that cases will continue to pop up over the summer,” he said.

Dr. Nissola told CBSN Boston that travelers circulating the Delta variant in Provincetown could pose a risk to the local community.

“We don’t know if these breakthrough cases are infecting other people,” he said. “We don’t know if the communities that are just trying to go about their day are being affected by this new flood of people in P-Town.”

Louisa Moller