Incubation time, contagious peak and presence in saliva … The characteristics specific to the Omicron variant question screening protocols.
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A negative autotest result followed by a positive PCR, negative antigenic tests despite typical CVIV-19 symptoms, people within the same home that have the same symptoms but not the same test results. … The testimonials evoking diagnostic discordances multiply while the Omicron wave continues to overlook the French population at the peak of 2.5 million new contaminations in one week.
This discrepancy is primarily explained by an increased use for a few weeks with autotontes and antigenic tests, less sensitive than PCR tests, so far main tools used for the diagnosis. Autototes are indeed antigenic tests on nasal levy made at home that cause many false negatives, especially one in two cases in the asymptomatic. For their part, in winter, the antigenic tests on nasopharyngeal samples produce more false positives when used at too low temperatures, for example in the barnums outside pharmacies.
“However, we are now facing Omicron, which behaves different from the previous variants and for which one is recovering data”, notes Cédric Carbononneil, head of the service evaluation of professional acts at the high Health authority (HAS). Should these false results alert us that the test compass has lost the north face the peculiarities of the Omicron variant?
a reduced sensitivity against Omicron?
The first signal came at the end of December of the United States, where the agency responsible for the sale of drugs has sown doubt in a line : “First data suggest that antigenic tests detect the Omicron variant but can have reduced sensitivity.” Which means that false negatives would be more common with Omicron than with previous variants. A statement confirmed by a team of Swiss researchers who evaluated eight antigenic tests against Delta and Omicron variants. “We observed a slightly lower sensitivity with Omicron”, explains to the world virologist Isabella Eckerle, who led The study
“All quick tests do not work in the same way: Some were still sensitive for Omicron as for Delta, some have shown lower sensitivity,” she adds. First results to take a decline therefore, and which vary according to the products distributed in each country. However, for Cédric Carbonon, these data should not worry too much “because if there is really a problem with the sensitivity of the tests, we would not have detected as many cases Omicron since December”.
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