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If you’re using a rapid test to lower the risk of a holiday gathering, make sure you take it on the same day of the event, preferably about 15 minutes before you walk in the door. Recently, a Christmas party in Norway became a superspreader event even though everyone was vaccinated and had used a rapid test. But in that case, people tested one day before the event.
Two tests are better than one. The biggest mistake people make using rapid home tests is taking a single test and thinking it means they don’t have Covid-19. If you’re worried that you’ve been exposed to Covid, you should take at least two tests over a three- to four-day period. The Centers for Disease Control and Prevention says the best testing window after a potential exposure is to test three to five days after the high-risk event or contact with an infected person.
The Coronavirus Pandemic: Key Things to Know
The bottom line is that the more often you use the tests, the better, said Dr. Michael Mina, a former Harvard epidemiologist who is now the chief science officer for eMed, a company that verifies at-home test results. If you want to spend time with a medically vulnerable person, you should take a test a few days before seeing them, and then take another test on the day of the visit.
“Think about, How do I test as close as possible to the thing that I’m doing?” Dr. Mina said. “When I go visit my parents, I always bring rapid tests with me. Right before I walk in the door, I use the test in my car.”
What do I do if the test is positive?
Most of the time, a positive result means you have the coronavirus, particularly if you have symptoms. But false positives do happen. Recently, Ellume, an Australian company, recalled nearly 200,000 test kits because of concerns about a higher-than-expected rate of false positives.
If there’s reason to doubt a positive result, take another test, preferably from a different manufacturer or at a testing center. People hosting large events, like weddings, and using the tests to screen guests should have a few extra tests on hand from a different brand for those guests who test positive. You can be confident in the result if the second test is negative, Dr. Mina said.
“It would be really rare for someone to have a true positive and then have a second test show a false negative result,” he said. “If you’re having a dinner, you may as well just cancel dinner if someone tests positive. But if it’s a high-consequence event, like you’re having a wedding and flying somewhere, and you’re going to screen a few hundred people, you may get a false positive and want to test again.”