Can we trust rapid COVID tests against BA.2? This is what the experts say
COVID-19 cases have been slowly ticking up in the U.S., with the omicron BA.2 subvariant now the dominant strain in the country. At the same time, rapid at-home antigen tests have become the first choice diagnostic tool for many people who think they might be infected.
While these rapid tests are useful in detecting the spread of COVID-19, the high infectivity of BA.2 and concerns around self-reporting have given rise to a number of questions.
Here is what two health experts have to say.
Rapid antigen tests work against BA.2, but there are some caveats
Although we've long known that rapid tests have a lower degree of accuracy compared to the standard PCR test, there is no indication they are any less effective at detecting BA.2 than previous variants we've seen.
That said, rapid tests might take longer to yield a positive result, according to Dr. Celine Gounder, a senior fellow and editor-at-large for public health at Kaiser Health News.
"There's usually a day or two delay between when you might test positive on a PCR versus when you might test positive on one of these at-home rapid antigen tests," Gounder said. "But they do work to pick up an infection, and they should be used frequently."
However, given the higher infectivity of BA.2, there is a chance that the virus might infect others before a positive result is seen on a rapid test, according to Dr. Wilbur Lam, a physician and biomedical engineer who works with the federal government in assessing COVID-19 diagnostic tests.
"One aspect about omicron [including the BA.2 subvariant] is biologically, it likely is more infective than the other previous variants," Lam said. "So the test might not even have time to pick it up before it jumps from one person to another person."
Nevertheless, rapid antigen tests have the advantage of being widely available and delivering a result within minutes, he said. The key to using them effectively against BA.2 is to test early and frequently.
"Because these things are more available than PCR testing, each person, if they're able to get hold of them, can test themselves serially," Lam said, adding that people should test multiple days after the onset of symptoms.
"That serial testing does end up mitigating the drawbacks of at least the accuracy of these types of tests compared to PCR tests."
Have some symptoms but test is negative? Context is key
Some people may find they have symptoms consistent with a COVID-19 infection, but they are still testing negative on rapid tests. If you find yourself in a situation like this, Lam says context is key for determining what to do next.
If you continue to test negative, he said you might be fine to carry on with your daily life, as long as you aren't planning on being around people who are immunocompromised.
However, if you plan on being around people who are at higher risk of severe illness, you should consider taking extra precautions for their sake.
"[If] you're going to visit, for example, an elderly family member who is immunocompromised due to cancer and chemotherapy, that's when I would say take some extra precautions, even if you're negative," Lam said. "So continue to mask, test again, maybe get a PCR test."
If people aren't reporting the results from their rapid tests, can we trust the data?
While at-home tests make it easier for people to detect a COVID infection, the current data might not reflect actual infection rates if there is a lack of self-reporting.
"This is an important question that the governmental, medical and public health communities are just now scratching the surface of," Lam said. "In fact, the current BA.2 case numbers may be underestimating the true numbers because a significant number of positive cases are self-detected and unreported."
And while some rapid tests offer smartphone apps to help people self-report a positive result, there isn't any requirement to do so.
The Centers for Disease Control and Prevention encourages people to report any positive results to their health care providers, who can make sure they receive the appropriate medical care. That could include specific treatments if necessary.
According to the CDC: "The public health community, including CDC, is confident that situational awareness remains strong without receiving self-test results."
New tests work best. But expired tests might still work for a time
Currently, every household in the U.S. is able to order two sets of four free at-home tests throughcovid.gov. However, these tests don't last forever and additional tests are not free.
Both Gounder and Lam say it's best to follow the manufacturer's suggested expiration date. However, if you have an old rapid test on hand, they say it could be useful for a time, although there's no consensus on exactly how long.
"The rapid tests are fundamentally biological and biochemical in nature and bear some similarities to food products, at least as far as the expiration date is concerned," Lam said. "Therefore, a test will not go 'bad' immediately after the expiration date but will gradually degrade over time."
Gounder suggests storing tests in order of expiration date so that you are using the oldest ones first.
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