We’re well into the holiday season, and while experts advise skipping in-person celebrations this year, many are wondering how they can gather in a way that’s safer.

First, it should be noted that due to the rise in COVID-19 cases, all public and private indoor gatherings are banned in Philadelphia through the New Year. The city also recently announced that food and drink are prohibited at outdoor gatherings. And statewide, Pennsylvania Health Secretary Rachel Levine encourages residents not to hold holiday gatherings with anyone outside their household.

If you’re thinking about getting together anyway, can testing save the day? If every guest gets a test, how much will that lower the risk of spreading coronavirus among your family or friend group? The answer is complicated, but in short: Testing isn’t foolproof.

The incubation period makes testing tricky.

The coronavirus incubation period ranges from two to 14 days, with a median time of 4 to 5 days from exposure to the onset of symptoms. Once exposed, the virus needs time to replicate to a level that can be detected by testing.

If you were exposed the day before you get tested, and you test negative, you could still develop symptoms a few days later,” says Patricia Henwood, associate professor of emergency medicine at Thomas Jefferson University’s Sidney Kimmel Medical College and leader of the Emergency Medicine COVID-19 Task Force at Jefferson Health.

If you quarantine for a minimum of a week prior to testing, you can gain a higher confidence in test results, Henwood says. But even then, they won’t be 100% reliable.

“The full incubation period is up to 14 days, so it becomes more about how much risk mitigation you’re trying to do and what level of risk tolerance people are comfortable with,” says Dr. Eric Sachinwalla, medical director of Infection Prevention and Control at Einstein Medical Center Philadelphia.

Before symptoms appear, if you get infected, you could test positive but you could also test negative. There’s also the possibility of receiving a false negative result.

False negatives: ‘A negative test is not the end-all-be-all’

A false negative is a test that indicates you don’t have COVID-19 when you actually do. And a false positive is a test that says you have the virus when you aren’t actually infected.

No test is 100% accurate, including those for coronavirus. False positive rates are lower, but both false positives and negatives happen.

“A negative test is not the end-all-be-all,” says Sachinwalla. “I’ve seen [false negative rates] anywhere from 10% to 40% depending on the type of test that’s done and the situation.”

There are two testing options to test for current infection, and there are pros and cons to both. PCR or viral tests are known to be more accurate, but turnarounds for results are often longer. Antigen tests can produce on-the-spot results, but produce a higher rate of false negatives.

Interpreting test results isn’t clear-cut.

Testing is important for everyone who develops symptoms that match coronavirus. It will determine how long you need to isolate at home and if contact tracing is necessary.

“If a person is symptomatic and they test positive, that’s easy — they’re positive. But if they’re symptomatic and test negative, then you have to look at the whole picture,” says Sachinwalla.

Because of false negatives, there are other factors to consider before ruling out coronavirus. Primarily, you want to determine your likelihood of exposure. That means looking at how many people you’re seeing in person and where else you might be encountering risk. No matter what a test says, you shouldn’t go to any kind of celebration right now if you’re feeling sick.

But what happens if you don’t have any symptoms? If you’re getting a test so you can see family, that’s likely the reality. In this case, interpreting test results becomes even trickier.

“There are gradients. If you’ve been seeing friends on weekends or dining out, and then you go get a test, you have a higher pretest risk,” says Sachinwalla. “A negative test result won’t necessarily reduce your risk [of spreading COVID-19] as much as someone who’s been working from home and getting deliveries.”

When you’re not feeling sick and you test negative, you need to consider factors like false negatives, the type of test, and when you may have been exposed versus when you got tested. Again, you could be exposed today, get tested tomorrow, and receive negative results.

If you don’t quarantine after testing, the results lose their value.

Then there’s the final testing challenge: You could become exposed in the time between getting tested and your gathering.

Testing results typically take at least a few days to get back, especially for PCR tests, which need to be sent to a lab for processing. Currently, with COVID-19 cases rising, many labs are becoming inundated, creating longer wait times.

If you can’t afford to quarantine between the time of the test and your holiday gathering, the results lose their utility.

“Testing can definitely help, but it only provides you with information in the moment. And is it enough to mitigate all of the risk? No,” says Sachinwalla. “I know this isn’t what holidays are meant to look like, but skipping this year may mean there’s a next year to go to.”