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Some people have said they have COVID-19 symptoms but test negative on rapid antigen tests.
This may happen when it’s still early in the infection period and there’s not enough virus present.
This may also start to happen when variants mutate.
The FDA recommends following up with a PCR test if antigen tests come back negative but the symptoms are highly suggestive of a COVID-19 infection.
Antigen tests that are ready in 15 minutes and can be stored and used at home have been crucial for many who are trying to mitigate risk of contracting the coronavirus. But now some people with COVID-19 related symptoms are reporting that they are repeatedly testing negative on at-home rapid tests. This has brought up the question of whether these tests are working for newer omicron variants.
This might also happen if the SARS-CoV-2 virus changes enough so that the part that binds to the rapid antigen tests isn’t as good of a match. “As mutation occurs, it may somehow change the structure of these different proteins, which may result in a decrease in detection by the antigen testing,” said Esther Babady, who is chief of the clinical microbiology service at Memorial Sloan Kettering Cancer Center in New York, to CNBC. “It can also be that earlier in the infection by BA.4 and BA.5, you don’t produce enough of the SARS-CoV-2 protein.”
With the current variants, it seems that the antigen tests still work, although the timing of when you take the test may matter more or the sensitivity of the test to pick up an infection may be less than with previous variants.
“Early data suggests that antigen tests do detect the omicron variant but may have reduced sensitivity,” the Food and Drug Administration (FDA) state on their website. “It is important to note that these laboratory data are not a replacement for clinical study evaluations using patient samples with live virus, which are ongoing.”
The FDA are consistently testing the various brands of rapid antigen tests and maintain an updated list of authorized tests.
“The FDA would know if there are performance concerns because they continue to monitor all authorized tests and scientific evidence over a period of time in the event that they need to make changes,” Mark Fischer, who is the Regional Medical Director at International SOS, said in an email to CNET.
If in doubt, people can turn to PCR tests. If someone is testing negative with antigen tests but is suspected to have COVID-19, following up with a PCR test is important for determining if it is a coronavirus infection, according to the FDA’s recommendations. Although PCR testing may be less accessible than previously during the pandemic, it is still the most surefire way to find out if someone is infected.
“If someone has a high suspicion of having BA.5 and their antigen test is negative, a PCR test will really rule it out,” says Babady.