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PCR or rapid antigen? Here’s how to use COVID tests to gather safely for the holidays

Rapid tests are a good way to get an immediate answer so you can start quarantining to protect others if you do test positive, said Dr. Brian Hollenbeck, chief of infectious disease at New England Baptist Hospital, but they should be followed up with a PCR test if you have symptoms or have been exposed.Craig F. Walker/Globe Staff

With Massachusetts facing a new surge in COVID cases, experts are pointing to both molecular and antigen tests as useful tools to stay safe this holiday season.

Both are diagnostic tests that can show whether you have an active COVID-19 infection and need to quarantine to prevent spreading the virus.

Polymerase chain reaction tests, better known as PCR tests, detect the genetic material from the virus, while rapid antigen tests detect specific proteins from the virus, according to the FDA.

So when is the best time to use each test, and how can they help us gather safely with friends and family?

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Dr. Brian Hollenbeck, chief of infectious disease at New England Baptist Hospital, said rapid tests can be helpful when you want an immediate answer, but they should be followed up with a PCR test for confirmation if you are symptomatic or may have been exposed to COVID.

“The downside [of antigen tests] is the testing is less accurate than PCR testing,” he said, pointing to an Omicron outbreak at a Christmas party in Norway last month where everyone had taken rapid tests the day before. “It’s not a perfect way to prevent COVID. But it is an added layer of protection and it’s slightly better than nothing.”

The problem is that both PCR and rapid testing are in very high demand, with limited appointments available, hours-long queues for walk-ins, and store shelves emptied of at-home rapid tests.

But if you are able to land a test, here is Hollenbeck’s advice for how to use it to stay safe this season.

Should you take a rapid test or a PCR test? (Or both)

PCR tests are more accurate and should be taken by anyone who has symptoms, like a cough or fever, or has been exposed to someone with COVID, he said.

But rapid tests are a good way to get an immediate answer so you can start quarantining to protect others if you test positive. Either way, if you are symptomatic or have known exposure, rapid tests should be followed up with PCR tests for confirmation.

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“It doesn’t really fully rule it out, but it helps to rule it in,” he said of rapid testing. At-home rapid tests can provide a result within 15 minutes, while PCR results can take days to get back, especially with the current high demand.

Rapid tests can also be handy for people without any symptoms or exposures who just want some peace of mind before gathering with others.

“There is value to doing a lot more testing as we go through Omicron,” Hollenback said. “When it’s positive, it can be very helpful in preventing a cluster or an outbreak.”

How confident can you be about the results?

False negatives with rapid tests are not uncommon, Hollenback said, so it’s important to confirm with a PCR if you have symptoms. False positives are also possible, though unlikely in symptomatic cases.

If you test positive on a rapid test without any symptoms or known exposure, there’s a small chance it could be false. But you should get a PCR test to confirm, he said.

“I would still stay away from family gatherings until you have the result of a PCR back,” Hollenback said.

How should you use a test to prepare for a holiday gathering?

For asymptomatic people taking a rapid test ahead of seeing friends or relatives, it’s best to take it as close to the event as possible, Hollenback said.

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“If you’re able to do it serially leading up to that then that adds additional validity to the testing, but can be harder to implement, especially when testing is so hard to get right now,” he said.

How can testing help us travel safely?

If you’re required to be tested for travel, take a PCR test, Hollenback said. Airplanes are generally safe because there is a good amount of air circulation and mandatory masking, he said.

“We don’t see a lot of transmission on airplanes, at least with prior variants,” Hollenback said. “But airports are a different picture.”

At airports, more unmasked people and large groups can increase the risk of transmission, so if you’ve been in one recently and want to get tested as a precaution rather than a travel requirement, a rapid test can be valuable, Hollenback said.


Sahar Fatima can be reached at sahar.fatima@globe.com Follow her on Twitter @sahar_fatima.