Emerging Data Raise Questions About Antigen Tests and Nasal Swabs

A new study adds to evidence that common rapid tests may fail to detect some Omicron cases in the first days of infection.

A small, new real-world study suggests that two widely used at-home antigen tests, the Abbott BinaxNOW and Quidel QuickVue, may fail to detect some Omicron infections even when people are carrying high levels of the coronavirus.

The study, which has not yet been peer-reviewed, focused on 30 people infected with the virus at five workplaces that experienced what were most likely outbreaks of the Omicron variant in December. The people received both saliva-based P.C.R. tests and rapid antigen tests using nasal swabs.

It took three days, on average, for people to test positive on a rapid antigen test after their first positive P.C.R. result. In four cases, people transmitted the virus to others while the rapid test showed the negative result, according to the study, which was conducted by several members of the Covid-19 Sports and Society Working Group.