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Most vaccinated healthy young adults who get COVID-19 no longer test positive for virus after five days, BU study says

A dose of the Moderna COVID-19 Vaccine is prepared.Pat Greenhouse/Globe Staff

Most healthy young adults who are vaccinated against COVID-19 but who contract the virus no longer test positive for it after five days, a new study from Boston University Medical School researchers has found.

In a statement Monday, the medical school said the study’s findings were recently published online in the journal Clinical Infectious Diseases.

The medical school said researchers collected daily anterior nasal swabs for at least 10 days from a group of college students and staff and found that in the majority of young, healthy and vaccinated adults, the infectious period for COVID-19 is limited, with only 17 percent remaining positive after five days.


“As isolation can have a significant impact on both the economy of a country and the mental health of its citizens, it is imperative to make efforts to reduce isolation periods while simultaneously preventing infectious individuals from spreading the disease,” said Dr. Tara Bouton, a corresponding author of the study and an assistant professor at the medical school, in the statement.

The research team, the statement said, recruited study participants from a campus that had a multi-faceted surveillance testing and COVID-19 control program. The statement didn’t identify the campus but said researchers believe the study bolsters support for guidelines for strict masking beyond the initial five-day isolation period for COVID-19 infections, to help prevent transmission.

“We believe that rapid antigen testing may provide reassurance of lack of infectiousness, though masking for a full 10 days is necessary to prevent transmission from the 17 percent of individuals who remain culture positive after isolation,” Bouton said.

Under guidance released by the CDC in late December, isolation restrictions for people infected with COVID-19 were shortened from 10 days to five days if they no longer feel symptoms or feverish. After that period, the CDC asks people to spend the next five days wearing a mask when around others.


The CDC website recommends people who test positive for COVID-19 with symptoms end isolation after five full days “if you are fever-free for 24 hours (without the use of fever-reducing medication) and your symptoms are improving.”

The site recommends people who test positive but do not experience symptoms end isolation five full days after a positive test.

In addition, the CDC recommends that patients who become very sick from COVID-19 or who have weakened immune systems isolate for at least 10 days and consult their doctors before coming out of isolation.

Material from the Associated Press was used in this report.

Travis Andersen can be reached at travis.andersen@globe.com.