Rapid antigen tests (RTK-Ag) may not be sensitive enough to catch early cases of Covid-19 infection involving the Omicron variant until a patient is already highly infectious, a study suggests.

“The policy implication is that RTK-Ag tests may not be as fit-for-purpose in routine workplace screening to prevent the asymptomatic spread of Omicron, compared to previous variants, given the shorter time from exposure to infectiousness and lower infectious doses sufficient for transmission,” the study authors wrote.

The US-based study analysed 30 Covid-19 cases between Dec 1 and 30 in New York, Los Angeles, and San Francisco.