epidemiology-public-health-implementation, science-brief
| February 10, 2022
Use of Rapid Antigen Tests during the Omicron Wave
The emergence of the now provincially and globally dominant SARS-CoV-2 Omicron variant demands a reassessment of the diagnostic performance of rapid antigen tests.
Rapid antigen tests are less sensitive for the Omicron variant compared to the Delta variant in nasal samples, especially in the first 1-2 days after infection. However, rapid antigen tests can more reliably detect infectious cases of the Omicron variant in combined oral-nasal samples. Individuals can collect these samples by initially swabbing both cheeks, followed by the back of the tongue or throat, and then both nostrils.
In light of currently very high SARS-CoV-2 transmission rates in Ontario and the limited sensitivity of rapid antigen tests for the Omicron variant, a single negative rapid antigen test result cannot reliably rule out infection; a single negative test result is not conclusive and should not be used as a green light for abandoning or reducing precautions. Conversely, in this context, an individual with a positive rapid test result should be considered and managed as a case of COVID-19 and should immediately isolate; additional confirmation by polymerase chain reaction (PCR) is not necessary in most settings.
If asymptomatic testing strategies are considered, rapid antigen tests need to be performed frequently to be effective. When using ‘Test-to-Stay’ strategies as an alternative to large-scale isolation, asymptomatic close contacts of a positive case need to do rapid antigen testing daily. When using ‘Voluntary Asymptomatic Screen Testing’ strategies, asymptomatic individuals should do rapid antigen testing 3-5 times per week.
