In the lead-up to Thanksgiving, Americans are no strangers to planning. But this year, as they prepare to let turkeys brine and pie crusts thaw, people across the country are waiting for something extra: a coronavirus test they hope can clear them to mingle with loved ones.
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% 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-19 response at Partners in Health. Yet this is a common misperception contact tracers hear when talking to people, he said.
The experts agreed that tests were very useful for one thing: If someone receives a positive test, that person knows to stay home and isolate.
But a negative test, while helpful, is not sufficient, said Dr. Esther Choo, an emergency medicine physician and a professor at Oregon Health and Science University. A test “filters out those who are positive and definitely shouldn’t be there,” she said. “Testing negative basically changes nothing about behavior. It still means wear a mask, distance, avoid indoors if you can.”
Not All Tests Are Created Equal
Different tests for the coronavirus give different information.
Laboratory tests that rely on a technique called polymerase chain reaction, or PCR, can detect the virus when it’s present even at very low levels. But it might take a couple of days to return results, leaving time for someone to be exposed. Antigen tests are faster, less expensive and more convenient — they can deliver results in a matter of minutes — but are also more prone to missing the virus when it’s scarce. To receive emergency authorization from the Food and Drug Administration, antigen tests for the coronavirus need to detect only 80% of the infections found by PCR. Many rapid tests also aren’t authorized for use in people who don’t have symptoms.