A small real-world study that has not been peer reviewed demonstrated that patients were infected with SARS-CoV-2 for several days before rapid antigen tests detected Omicron in their specimens.
The study was conducted by the COVID Sports and Society Workgroup and reported as an early release by MedRxiv.
The rapid antigen tests kits used were Quidel QuickVue At-Home OTC COVID-19 Test and Abbott BinaxNOW COVID-19 Antigen Self-Test.
“The objective of this study was to describe the discordance in saliva SARS-CoV-2 PCR and nasal rapid antigen test results during the early infectious period,” the researchers said.
To conduct the study, researchers included 30 study participants who were diagnosed with Covid-19 between December 1-31, 2021, at five workplaces in New York, NY, Los Angeles, CA, and San Francisco, CA.
The populations were fully vaccinated by employer mandate and had received booster doses.
To isolate the window of acute infection, cases were included if they received daily testing at the time of diagnosis and had SARS-CoV-2 quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) test results and rapid antigen test results from specimens collected at the same time.
The study found that the median time from the first positive PCR test to the first positive antigen test was three days.
The study follows an updated guidance from the U.S. Food and Drug Administration (FDA) in which the agency said that antigen tests The FDA said early data suggest that antigen tests detect the Omicron variant but may have reduced sensitivity than for other SARS-CoV-2 variants.
In statements issued late last year, both companies expressed confidence in the ability of their tests to detect Omicron.