Rapid Coronavirus Tests: What They Can Do & What They Cannot

Recently, the U.S. Food and Drug Administration (commonly referred to as the FDA) granted approval for the emergency-use of small, rapid coronavirus tests.

These tests are estimated to cost under the U.S. $5, are roughly the size of a credit card, and only take about 15 minutes for processing. The most interesting part? There’s no lab or machine used for processing.

These rapid antigen tests are technically designed to tell if a person is infected with SARS-CoV-2, the virus that causes the coronavirus disease 2019 (COVID-19). But how effective will they truly be, what are they capable of, and most importantly, what are they not capable of?

Though these rapid antigen tests are estimated to help the testing capacity of the United States—which has been reported to lead the world in COVID-19 deaths and lag in testing capacity—it’s uncertain how effective these cheap, fast tests will be. Especially when compared to the gold-standard tests that detect viral RNA using a technique called the polymerase chain reaction (PCR).

What Can Rapid Antigen Coronavirus Tests Do?

When it comes to the rapid coronavirus tests, they do bring quite a few capabilities to the United States’ testing ability. The test is designed to detect specific proteins called antigens that are on the surface of the virus. Technically, this test can identify the virus within hosts at the peak of their infection when the virus levels within a body are at an all-time high.

Antigen tests are helpful because they’re cheap and rapid—they can be distributed quickly and efficiently in an effort to keep the pandemic at bay. Primarily, they could be used to spot those who are at the greatest risk of spreading the disease to others. These tests have been used—and continue to be used—in other countries like Italy and India.

Further, while these tests are currently only being distributed by trained professionals, this version of testing would be easily adapted for at-home tests, making it easier and safer for those infected to get tested.

What Can’t Rapid Antigen Coronavirus Tests Do?

Unfortunately, rapid antigen coronavirus tests are not as effective or accurate as RNA tests. Antigen tests aren’t as sensitive as the PCR versions, which means they’re unable to pick up the minuscule amounts of SARS-CoV-2 virus that can cause COVID-19.

Ultimately, this means that if someone is still infected and contagious but isn’t at the peak of the virus, they could test negative for the virus—which could result in an outbreak. The viral load a host carries of SARS-CoV-2 peak very early in the infection, then it gradually declines—with tiny amounts of virus RNA staying in a host’s nose or throat for a few weeks (possibly months). The issue here is that a rapid antigen test may not be able to pick up these different viral levels. So, if a host doesn’t get tested during their peak, the test could come back negative. There is evidence that hosts are unlikely to spread the virus about 8-10 days after showing symptoms.