The genetic mutations in new strains of the coronavirus could affect the results of some COVID-19 tests, according to a warning from the Food and Drug Administration (FDA). Because the mutations affect the part of the virus’s genetic material that these tests look for, the tests could end up giving a false negative result, meaning the results are negative but an infection is present.
The FDA recently discovered that three particular COVID-19 tests could give a false negative result if the sample contains the B.1.1.7 variant of the virus, which triggered the London lockdown in December. It has since spread to other countries, including the U.S. The risk for a false negative in this situation is low, according to the letter. But the FDA is flagging the issue to health care workers and lab staff.
Those three tests—the Accula SARS-Cov-2 Test, the TaqPath COVID-19 Combo Kit, and the Linea COVID-19 Assay Kit—all work by detecting specific parts of the coronavirus’s genetic material. Tests like these, which rely on polymerase chain reaction (PCR) technology to amplify small amounts of viral genetic material to detectable levels, are generally considered the gold standard.
Both the TaqPath test and the Linea test are designed to detect a part of the virus’s genetic material that affects its spike protein, which also happens to be the location of one of the mutations present in the B.1.1.7 variant. But that isn’t the only target that those tests look for, so the FDA says “the overall test sensitivity should not be impacted.” Even if the test fails to detect one target area of the virus it is looking for because of a mutation in that region, the test should still pick up the virus with its other testing target(s).
And when it comes to the Accula SARS-Cov-2 Test, its results might be affected if the strain has a different genetic mutation, one that has been detected in some variants, but is not present in B.1.1.7.
Overall, the FDA “believes the risk that these mutations will impact clinical sensitivity is low,” meaning that in practice, it’s unlikely that these tests will actually be less sensitive at detecting cases of COVID-19. But the FDA is generally advising providers to be aware of the ongoing potential for false negatives as new genetic variations arise.
That’s why it’s important for providers to take other factors into account when making a diagnosis, including the patient’s symptoms and epidemiological data for their location. (For instance, if someone has COVID-19 symptoms and is living in an area where the virus is spreading rapidly, a negative test result is likely worth reevaluating.) And if COVID-19 is still suspected following a negative test result, the FDA recommends retesting the patient using a different test, with different genetic targets.
Finally, it’s important to keep in mind that although the the B.1.1.7 variant that’s been grabbing headlines is associated with an increased risk of transmission, according to the Centers for Disease Control and Prevention (CDC), it does not appear to cause more severe illness or be more deadly. And, importantly, experts say it seems as though the COVID-19 vaccines we currently have available will be just as effective against these strains.