You can still be contagious with COVID if you have a negative test — here’s why | The Transmission

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As the nation experiences what many experts believe is the second-largest wave of COVID infections since the pandemic started, many Americans will be checking to make sure they don’t have the respiratory illness.

COVID testing guidelines and what we know about how long you’re contagious have changed since the start of the pandemic. So we sat down with a leading epidemiologist, who provided guidance on which tests to do, when to do them and how to interpret them.

When should you test for COVID?

If you have COVID symptoms, you should take a test immediately, according to the U.S. Centers for Disease Control and Prevention.

If you were exposed to COVID, you should take a test at least five days after your exposure.

If you don’t have symptoms or any known COVID exposures, you can may also consider testing before an even where you’ll encounter a lot of people or if you’re spending time with someone high risk for severe illness, such as an older or immunocompromised person. Test right before the event or visit, if possible.

How accurate are COVID tests now?

A positive result on an at-home COVID test is very reliable, according to the CDC. However, a single negative result with an at-home test may not be accurate because you may have taken it before the virus reached detectable levels.

That’s why, if you’re using at-home tests to detect an infection, you should test more than once.

If you have symptoms and test negative with an at-home rapid test, test again 48 hours later, the CDC advises. If you were exposed to COVID, do not have symptoms and test negative, test again 48 hours later. If that test is negative, test again another 48 hours later.

The emergence of new variants, in particular JN.1, has not affected the accuracy of at-home tests, TODAY.com previously reported.

If you want to take only one test, the CDC recommends what’s known as PCR test for the most reliable result. PCR tests are usually administered in medical settings, and they detect a virus’s RNA, which is similar to human DNA, Dr. Michael Mina, a leading epidemiologist and chief science officer at the telehealth company eMed in Miami, Florida, tells TODAY.com. (At-home tests are usually antigen tests, which look for proteins of the virus.)

He notes that PCR tests often stay positive for days or even weeks longer than people are contagious, making them ideal for diagnosing COVID, but less ideal for knowing when you no longer need to worry about spreading an infection to others.

Can you be contagious after a negative COVID test?

If you test negative with a PCR test, you are likely not contagious.

But if you test negative with an at-home test, the answer will depend in part “on whether the negative COVID test is at the beginning of feeling sick or on the way to recovery,” Mina says.

“If you have already been positive and are testing to see if you are recovering or recovered, then as soon as you become negative, it is appropriate to assume you are no longer infectious,” he explains.

When a positive rapid antigen test goes from a dark line to a very faint line, this means that the virus load in the swab is probably less than when then line was dark, he adds.

“So even a faint line after a really dark line means you are likely much less contagious, and no line means you are likely very low risk of being infectious,” Mina says.

But at the beginning of an COVID illness, an at-home antigen may come back negative, even though you may become infectious as the viral load increases.

“You may be starting to feel symptoms because your immune system is activating, but the virus might not yet be high enough in your nose to cause a test to turn positive,” Mina says. In this scenario, you may test positive several hours later, the next day or the day after that.

If you get a negative at-home test result at the beginning of a possible infection, keep the following guidance from the U.S. Food and Drug Administration in mind when weighing your risk of having COVID: