Demand for Covid-19 tests is surging amid the spread of the omicron variant. While some people have questioned if rapid tests can accurately detect omicron, experts say the tests work, even for the new variant.
Going into the holidays, health officials have encouraged Americans use rapid tests before they gather with friends and family to cut down on potential viral transmission.
"For that extra reassurance, as we have more disease in this country right now, do a test and make sure that you're negative before you mix and gather in different households," said CDC Director Rochelle Walensky.
However, amid increasing demand for Covid-19 tests—especially as the omicron variant continues to spread across the United States—many Americans are struggling to get tested quickly and easily.
In several large cities, including Miami and New York City, people are waiting in lines for hours to get tested at medical clinics or testing centers, the New York Times reports. In addition, some laboratories have reported longer wait times—up to three to five days—for results as they struggle to deal with increased testing volume.
Rapid at-home tests are in limited supply despite efforts from the Biden administration to increase production. Around the country, both physical and online retailers are struggling to keep rapid tests in stock, the Times reports.
"If omicron continues to spread as fast as it appears, we'll be very challenged on any reasonable number of tests, particularly prophylactic testing before gathering," said Mara Aspinall, an expert in biomedical diagnostics at Arizona State University, "and that is a huge concern."
In addition to concerns about accessing tests, some people are wondering whether rapid tests can detect the new variant, MedPage Today reports.
According to Michael Mina, a former epidemiologist at Harvard University and current chief science officer at eMed, one reason why people may be concerned about rapid tests and omicron is because some individuals can be symptomatic but still test negative.
According to Mina, early coronavirus symptoms are often driven not by the virus itself but by the immune system's response, which is bolstered by vaccines. As such, some people—especially those who have been vaccinated—may start displaying symptoms before the viral levels in their nose have reached a level detectable by rapid tests.
"This is literally a reflection of the fact that vaccines are doing their job," Mina wrote on Twitter. He added, "We recognize the virus quickly after it lands in us, we develop symptoms, we kind of fight it off, then it often eventually wins, and grows fast AFTER immunity/symptoms started."
One implication is that people who are symptomatic and test negative should still be "very very cautious" and retest "the next morning or that night" in case they actually do have a coronavirus infection, Mina wrote.
More broadly, Mina said rapid tests should still be able to detect the omicron variant since most tests detect the coronavirus's nucleocapsid protein instead of its spike protein, which is where most of omicron's mutations are. "Omicron has four mutations in [its nucleocapsid]," Mina wrote in a tweet. "Two were in Alpha/Delta and were fine. Two are in ... a non-immunogenic site [and are] unlikely to impact rapid tests."
Separately, Abbott Laboratories, which manufactures one of the most popular at-home rapid tests, released a statement saying both its rapid tests and PCR tests can detect omicron, providing a similar explanation to Mina's. "While the omicron variant contains mutations to the spike protein, Abbott's rapid and molecular tests ... do not rely on the spike gene to detect the virus," the company said.
In addition, the United Kingdom's Health Security Agency on Friday published data showing that rapid tests were effective at detecting the omicron variant. For the small study, the agency tested five rapid tests against 15 omicron samples at different dilutions and found that none of the tests returned false negative results.
However, Mina noted that rapid tests could be less effective at detecting omicron if it spreads and replicates in the body differently than delta.
"If [omicron] transmission is able to occur at low viral loads then this becomes a much more difficult [variant] to test for before transmission," Mina wrote. "If omicron is able to more efficiently replicate in [the] bronchus (not measured by nasal swab), lyse, and release much more efficiently, then we may be in a situation where the amount of virus measured in the nose on any test may not correlate as well with exhaled virus."
Furthermore, if omicron replicates more quickly, rapid test results may only be accurate for a short time, MedPage Today reports. For example, it might be possible for an individual to test negative in the afternoon only to test positive later in the night after being at a party.
However, Mina said that, overall, "all the [current] data is in fact showing the rapid tests DO detect omicron as well as well as they detected delta." (Owens, Axios, 12/21; Frazier, Axios, 12/18; Stolberg/LaFraniere, New York Times, 12/17; Fiore, MedPage Today, 12/20)
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