Many people consider a negative coronavirus test to be a ticket to freely socialize without precautions. But scientists and doctors say this is dangerously misguided. It is one precautionary measure but does not negate the need for others, like quarantining, masking and distancing.

The main reason is that a test gives information about the level of the virus at one point in time. A person could be infected but not have enough virus yet for it to register on a test. Or, a person may become infected in the hours or days after taking a test. Also, the tests do not have 100 percent accuracy.

“If you require all of your guests to email you a negative test result before your Thanksgiving dinner, it will definitely decrease the risk of an outbreak — but not completely,” said Dr. KJ Seung, chief of strategy and policy for the Covid response at Partners in Health. Yet this is a common misperception contact tracers hear when talking to people, he said.