the staff of the Ridgewood blog
Ridgewood NJ, as the SARS-CoV-2 virus mutates over time, changes in its genetic makeup could impact the ability of certain tests to recognize and detect viral antigens. A preprint study posted to medRxiv this week raises questions about the reliability of at-home rapid antigen tests in the early days of infection with the highly mutated Omicron variant of concern (VOC). The small real-world study, which is not yet peer-reviewed, examined test results from 30 people who, because of their workplace rules, were undergoing both rapid antigen and polymerase chain reaction (PCR) tests on a daily basis. On days 0 and 1 following a positive PCR test, both of the at-home rapid antigen tests in use—Abbott BinaxNOW and Quidel QuickVue—produced false-negative results despite the presence of viral loads high enough for transmission. The researchers confirmed that 4 cases transmitted the virus between false-negative test results and noted there likely were more transmissions that were unconfirmed. On average, it took 3 days for people to test positive on a rapid antigen test after testing positive on a PCR test. The researchers shared their results with US CDC and US FDA officials and called for the real-world performance of rapid antigen tests to be reassessed for each new VOC.
The study’s results suggest that even if the supply and accessibility of at-home tests were sufficient, rapid antigen testing might not be reliable as an early warning, when people are most infectious and before symptoms begin. Although these findings warrant further study, scientists and public officials are urging the public to continue rapid testing but to use caution when interpreting the results. Some evidence suggests that Omicron might replicate more quickly and efficiently in the throat and mouth than in the nose. And while some individuals have reported swabbing their throats and noses in the hope of increasing the accuracy of test results, the FDA maintains the at-home tests should be used only as authorized. The agency recently updated its information on how SARS-CoV-2 variants could impact tests’ performance.