The best time to take a rapid test is right before you see vulnerable people or a large group.
Some disease experts also recommend waiting until you develop symptoms when testing is scare.
If you're symptom-free, but had a recent exposure, you can wait 3-5 days for a test, experts said.
COVID-19 rapid tests are flying off the shelves at pharmacies, in some cases selling out before they even arrive in stores.
Meanwhile, test manufacturers are struggling to keep up with recent demand. Many manufacturers assumed over the summer that there was limited use for rapid testing, since vaccines seemed to slow COVID-19 transmission and the Omicron variant hadn't been identified yet. Now the US is reporting nearly 600,000 COVID-19 cases per day, on average.
The Biden administration recently purchased 500 million at-home tests for Americans to order online for free, but even that supply could fall short. A November report from the Kaiser Family Foundation found that the US would need around 600 million COVID-19 tests per month if half the population tested weekly.
At the same time, high prices prohibit many Americans from buying at-home tests. Some of the most widely available rapid tests in the US, Abbott's BinaxNOW and Quidel's QuickVue, retail for around $25 for two tests.
For people who have access to just one rapid test, there's a way to maximize its use, disease experts told Insider.
"The ideal moment to take it is right before you visit your grandmother or right before you go to a party," said Dr. Sheldon Campbell, associate professor of laboratory medicine at Yale School of Medicine. "It's not two days or three days after to find out if you ran into a problem. It's to prevent problems."
Here are experts' recommendations for the best time to test under three common scenarios: when you're symptom-free and want to attend a gathering, when you've recently been exposed to COVID-19, and after you've developed symptoms.
Scenario 1: You don't have symptoms, but want to see people in a group setting
Omicron seems to spread quickly relative to other coronavirus variants. A December report from the UK Health Security Agency found that Omicron is roughly three times more likely to transmit among households compared with Delta. That means taking a test the day before a social gathering doesn't guarantee that you won't infect people at the party.
People can go from "undetectable" on a rapid test to a "very high" number of virus particles in 24 hours, Dr. Michael Mina, chief science officer at eMed, a biotech software company that enables at-home diagnostic testing, and former assistant professor in immunology and infectious diseases at Harvard School of Public Health, wrote last month on Twitter.
If you're about to join a group, you should take a rapid test "a few hours before leaving the house," Tim Spector, a professor in genetic epidemiology at King's College London, told The Guardian last month.
Scenario 2: You've been exposed, but don't have symptoms
It can take up to two weeks for COVID-19 symptoms to develop after a person is exposed to the virus, but a recent study from Norway found that Omicron symptoms usually appear around three days after exposure, on average. That's shorter than the time it takes for symptoms to develop after getting infected with Delta or another coronavirus strain (around four to five days, on average).
"If you know for certain you've had an exposure, it doesn't really pay for you to take a test earlier than 48 hours after that known exposure," Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health, told Insider. "Ideally, 72 hours is a nice window of time where that usually gives a virus like Omicron enough time to replicate."
Other experts recommend waiting to a little longer to take a test.
"If you are exposed to someone, you should really be testing five days after if it's a home test, because it takes about five days to turn positive," Dr. Jorge Moreno, an assistant professor of medicine at Yale School of Medicine, told Insider. "If you test too early in the course, it won't be positive."
Scenario 3: You have COVID-19 symptoms
Some experts recommended holding off on a rapid test to see if symptoms develop.
"If you've got to use one test and you're not about to do something risky, then wait for symptoms because we don't really know when the peak of viral shedding is in asymptomatic people," Campbell said.
Once you develop COVID-19 symptoms, you "probably have enough virus in your system to make a positive test," Pekosz added.
But experts cautioned that a negative rapid test doesn't always means you're in the clear.
"If it's positive, that's fine. You're good," Campbell said, adding, "But if it's negative early in symptoms, sometimes the viral load isn't up quite yet. And late in disease, when people start getting really sick, sometimes the viral load's already fallen."
The ideal test for a symptomatic person is a PCR instead of a rapid, Campbell said, since lab tests are better at picking up virus particles in saliva and nasal swabs.
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