Are antigenic tests effective in detecting the presence of the Omicron BA.2 variant, now the majority in the national territory? La Dépêche disentangles the true from the false on this question.
At the end of March, the number of Covid-19 infections is experiencing a spectacular increase in France. The fault lies with the BA.2 subvariant, highly contagious and now the majority in the country. As a result, the French are once again rushing to tests, in particular antigenic self-tests that everyone can do at home and that return an almost immediate result. A legitimate question then arises: are these tests less effective at detecting Ba.2? the office Make the point.
For Bruno Julia, president of the Union of Community Pharmacists of Occitania, the level of reliability is always the same: “Since the beginning of its commercialization, antigenic tests have sought to eliminate the N protein, which stands for nucleocapsid. forms the envelope of the genetic material of the virus Unlike the S protein, for peakit is not subject to the many variations of the virus”. According to the pharmacist, the N protein would have suffered “only 3 or 4 variations” since the appearance of the virus.
No decrease in efficiency
An observation shared by Etienne Decroly, virologist and researcher at the CNRS: “The N protein is the most abundant in coronaviruses, so it is often used as a marker in diagnostic tests”.
“The antigenic tests have been developed precisely to detect conserved and stable proteins of the virus, so as not to have the risk of going through detections. Therefore, at the moment there are quite a few variations in effectiveness”, explains the researcher.
Marie-Édith Lafon, head of the virology laboratory and biologist at Bordeaux University Hospital, agrees: “We are not aware of a decrease in the detection of the Omicron BA.2 variant, which is currently fully dominant, by antigenic tests. No study to date, indicating that a drop in effectiveness can be accessed,” he explains to our colleagues at southwest.
Increasingly reliable PCR tests
Can the effectiveness of antigen tests vary depending on the manufacturer? “In France, there are about thirty antigenic tests on the market. Some are French, others American or Chinese. Of all these tests, there is only one that will look for both protein S and N. All the others focus on protein N So, ultimately, there is not a big difference between the manufacturers”, explains Bruno Julia.
Note that despite the still stable efficacy of antigen tests, it is better to perform a PCR test if you have symptoms: “The reliability level of PCR is always higher. The technique is more sophisticated, finer and, therefore, allows a higher level of detection”, details the expert.