New study looks at failure of SARS-CoV-2 PCR and rapid antigen tests to detect positive results early

Jan. 6, 2022

A new study reported by the COVID Sports and Society Workgroup and reported as an early release by MedRxiv, suggests that antigen tests performed poorly to detect COVID during the early period of infection, despite high viral loads.  The tests used by the researchers included Quidel QuickVue and Abbott BinaxNOW.

The authors suggest that a measured approach to use of these tests for asymptomatic screening is needed. They recommend the use of molecular and PCR tests, and employing multiple layers of protection are helpful to reduce the risk of transmission. They found that based on viral load and transmissions confirmed through epidemiological investigation, most Omicron cases were infectious for several days before being detectable by rapid antigen tests.

The objective of the study was to describe the discordance in saliva SARS-CoV-2 PCR and nasal rapid antigen test results during the early infectious period. They identified a high-risk occupational case group of 30 individuals with daily testing during an Omicron outbreak in December 2021. The study is not yet peer-reviewed.

They reported that on days 0 and 1, all rapid antigen tests produced false-negative results, despite 28 of 30 pairs having infectious viral load within the range of confirmed Omicron transmissions in the test group. The median time from first positive PCR to first detectable antigen positive was three days. After infection was detected, a subgroup who received daily saliva PCR, nasal swab PCR, and nasal swab rapid antigen testing showed viral load peaked in saliva 1-2 days before nasal tests. All individuals in the test group developed symptoms within two days of the first PCR positive test.

The researchers concluded that the performance of COVID-19 diagnostic tests must continue to be reassessed with new variants of concern.

The U.S. Food & Drug Administration (FDA) recently reported they were monitoring and evaluating the potential impact of genetic variants on antigen tests. The FDA is collaborating with the National Institutes of Health's (NIH) RADx program to study the performance of antigen tests with patient samples that have the omicron variant. RADx recently performed preliminary studies evaluating the performance of some antigen tests using patient samples containing live virus, which represents the best way to evaluate true test performance in the short-term. Early data suggests that antigen tests do detect the omicron variant but may have reduced sensitivity.1

The manufacturers of the two tests used, had previously reported their tests could detect Omicron but they were continuing their evaluations.

After the discovery of the Omicron variant in late November, Quidel issued a statement that included the following, “While our studies are ongoing, the early data give us confidence that our American-made PCR and rapid antigen tests can detect COVID-19 caused by the Omicron variant. Quidel has been, and will continue to be, vigilant in evaluating our assays with both genetic sequencing and real-world virus sample studies to assure customers of our products’ efficacy as the coronavirus evolves.2

Abbott also stated on December 28, 2021, that ” Abbott has been intently monitoring the mutations of COVID-19 so we can ensure our tests can detect them. We've conducted lab analyses and tests on the Omicron variant from live virus, including from the first U.S. omicron case, and BinaxNOW detected the virus in all tests we performed at equivalent sensitivity as other variants. Additionally, our data from customer use has not shown any change in test performance. tests on the Omicron variant from live virus, including from the first U.S. Omicron case, and BinaxNOW detected the virus in all tests we performed at equivalent sensitivity as other variants.” 3

MedRxiv has the report

More on COVID