People with the Omicron variant of the coronaviruses may have less accurate rapid covid-19 tests. The Food and Drug Administration reported this week that some tests may have reduced specificity, which could lead to a higher rate of false negative results. The FDA still recommends that people use the tests as instructed.
The Omicron variant has quickly spread throughout the U.S. and world. The variant of the coronaviruses called Omicron has many more relevant changes than previous forms, which are allowing it to more easily cause illness. It is not yet clear how much of the milder nature of Omicron cases can be attributed to the high rates of population immunity. It is likely a mix of both.
Some tests designed to look for the virus may be more likely to fail if they use the wrong targets. There have been reports of people not testing positive despite being sick. There was no evidence that rapid antigen tests were less accurate than the three tests that failed to detect omicron. The conclusion has changed.
The FDA reported on Tuesday that it had conducted a lab analysis that found a potential problem with certain rapid tests. This newer analysis used live virus samples from patients, instead of heat-inactivated samples, which are thought to provide a better comparison to real world performance.
The FDA said that early data suggests that the omicron variant may have reduced sensitivity.
Sensitivity refers to the likelihood that a positive result will be true, and specificity refers to the degree to which a test is accurate. A person with a diagnosed disease will be told they don't have it if a test has a lower sensitivity. Someone with Omicron may be reassured that they are free of infections even if they have another variant.
The rapid antigen tests were less sensitive than other tests. People would not test positive for the virus as early as they would if they had taken a test. The advocates of rapid tests argue that they are still very good at detecting when someone is at their most infectious and thus spreading their disease. Rapid tests should be used to protect others from being exposed to the disease, not to let people know when they become sick.
It is not clear if rapid tests will be any less effective at their intended goal for Omicron. The FDA and other regulatory agencies are studying how well rapid and other covid-19 tests are doing in the real world and if Omicron has changed things. The agency is telling people to use rapid tests according to instructions.
If you test negative on a rapid test but still feel sick or suspect exposure to someone with covid-19, you should get a follow-up test. Users are recommended to take multiple rapid tests on successive days to rule out the possibility of a false negative.
