Here's How Long COVID Is Contagious and What to Do When You're Exposed

An infected person can start spreading COVID-19 two days before they have any symptoms

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So you've been exposed to someone with COVID-19. Or, at least, you think you have.

What now?

With cases on the rise and holidays ahead, NBC10 Boston asked three top Boston doctors on Tuesday to explain when someone is contagious, define exposure and the proper protocols -- whether vaccinated or not -- in a weekly series, "COVID Q&A."

How can I tell if I've been exposed?

Dr. Shira Doron of Tufts Medical Center said the classic definition of exposure to COVID-19 is when you've been within six feet of a person in the contagious stage of infection for at least 15 minutes.

"That doesn't mean that the virus wears the watch or carries the yardstick, but there has to be definitions in order to implement public health measures," Doron explained.

The U.S. Centers for Disease Control and Prevention refers to this definition of exposure as "close contact."  

The number of new, confirmed COVID cases is at a level not seen since February, according to the latest data. It comes as all adults in Massachusetts were allowed to get a COVID booster shot.

An infected person can spread COVID-19 starting from two days before they have any symptoms (or, for asymptomatic people, two days before they would test positive), until they meet the criteria for ending isolation.

What do I do if I've been exposed?

"If you're exposed and vaccinated, you are not required to quarantine," Doron said.

The CDC recommends that vaccinated people get tested five to seven days after exposure, even if they don’t have symptoms. The agency also recommends wearing a mask indoors in public for 14 days after exposure or until a negative test result.

"Massachusetts hasn't implemented that in a formal way," Doron said. "In fact, if someone who's infected speaks to a contact tracer and gives that person a bunch of names of people who meet criteria for exposure, the state will not have anybody call you if you're fully vaccinated because there are no specific requirements related to that exposure."

People who have not been vaccinated are subject to quarantine guidelines.

"Now, I want to specify the word quarantine is different from the word isolate. People use that word interchangeably," Doron said. "Isolate is what you do when you are infected. Quarantine is what you do when you've been exposed and could develop infection at any time."

In Massachusetts, there are three quarantine options; a two-week quarantine, a 10-day quarantine with symptom monitoring for an additional four days or a seven-day quarantine with a COVID test on day five, six or seven and if it's negative, the quarantine ends on day eight.

How is the definition of exposure different in schools?

Doron works as an unpaid advisor to the Massachusetts commissioner of education and was involved in developing school policies for coronavirus safety.

She explained that the definition of exposure for children and staff in schools differs from other public places. The differentiation was established at the end of the last school year, when children were brought back to into Massachusetts classrooms with desks placed three feet apart.

"Some of us scientists advocated for a revised definition of exposure in schools," Doron said. "What that means is, that if you're in a classroom setting and everyone's wearing masks, you need to be within three feet for at least 15 minutes to count as exposed."

If you're between three and six feet, you get notified of the exposure, Doron said, but there's no quarantine or other requirement if you're unless you're within three feet.

There is also an option to avoid quarantine for students who are exposed in a classroom, which is the test-and-stay program. Instead of being sent home, program allows students to attend school and participate in extracurricular activities every day, contingent on daily COVID-19 test results.

"You have a test in school and if it's negative, you get to go about your business within the building and any after school activities related to that," Doron explained.

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