A less virulent variant than its predecessor, much more contagious and spreading at lightning speed, especially among children. Since its update in November in South Africa, the Omicron strain has revealed its specificities and its differences with Delta. With him, the virus would first appear in the mouth and throat, before lodging in the nose.
Some experts then call for favoring saliva samples to detect this strain, which is now the majority in France, earlier. Should we review our screening strategy and move away from nasal swabs? This is the question posed by a study prepublished on the scientific platform Medrxiv and relayed by the New York Times. But is it possible and desirable?
Shorter incubation time than Delta
Omicron or Delta: for the government, the strategy is the same, you must be “tested as a priority in the event of signs of the disease or if you are identified as a contact person”. A race against the clock regularly accused of being lost in advance. This strategy “has always been unsuitable: we look for SARS-CoV-2 in symptomatic people, and then in their contact cases. Screening has therefore never taken into account the dynamics of the virus, and has therefore not made it possible to break the chains of contamination”, summarized for 20 Minutes epidemiologist and biostatistician Catherine Hill.
A delay dug a little more by the surging Omicron, which has the particularity of having a “faster” incubation period than Delta and which “multiplies faster in the body”, indicated the government spokesperson, Gabriel Attal, January 5. The time “before the onset of symptoms has dropped from five to three days”, added Professor Yazdan Yazdanpanah, member of the Scientific Council, on BFMTV.
The virus first present in the mouth, a point under study by the government
And if it multiplies faster, Omicron would also not manifest itself in the same way in the organism. When her son tested positive for Omicron, of which he was already showing symptoms, Laure immediately took an antigen test, which turned out to be negative. “It was only two days later, when doing a self-test, that the result was positive,” explains the young woman. At the end of December, the American Medicines Agency noted that rapid tests, in the presence of the Omicron variant, more often indicate a negative result despite an infection. Would the result of Laure’s first test have been positive with a saliva sample? With Omicron, “the virus would be less present in the nose, and perhaps you will show symptoms or be in contact, but have a negative result”, said Dr Jimmy Mohamed on Tuesday on France 5.
According to the authors of the study cited above, who studied the tests of covid patients in South Africa, the birthplace of Omicron, the reliability of the different samples would not be the same depending on the variant sought. If with Delta, the nasal swab is 100% reliable, it drops to 71% by saliva. Conversely, when it comes to Omicron, the reliability of the saliva test is 100%, compared to 86% with a nasopharyngeal swab. “The traditional approach to diagnosing respiratory infections has always been to favor nasal swabs,” explained the New York Times Dr. Donald Milton, respiratory virus expert at the University of Maryland. However, with Omicron, which “appears first in the mouth and throat, this means that the approach (…) for the tests is problematic”.
Saliva, a simple but complicated sample
But saliva does not only have advantages. “The saliva sample is not the most sensitive, it produces false negatives. What you have eaten or drank can alter the pH of the mouth and affect the result. It is much more random, so be careful, insists Gilles Bonnefond, spokesperson for Union of community pharmacists’ unions (USPO). And we must not forget that if Omicron dominates, there is still some Delta in France. For this strain, it is the nasopharyngeal sample that is indicated, and if it is not detected when it is more dangerous, it is not good”. To date, saliva tests are only indicated “as a second intention in contact persons for whom a nasopharyngeal swab is not possible”, indicates the High Authority for Health (HAS).
In addition, “saliva self-tests do not exist, adds the pharmacist. They can only be performed in the laboratory or as part of large screening operations, sometimes organized in schools with the ARS. The samples are analyzed in the laboratory and you have to wait several hours for the result. In terms of logistical efficiency, antigen tests, which give a result in minutes, win out.”
More practical for (convincing to) test children
But this study could change the game and find an important echo with parents. While Omicron is causing an exponential number of contaminations in children, forcing the government to constantly review health protocols in schools, testimonials from parents who are cautious about the idea of testing their offspring themselves are flourishing on social networks. Some do not hesitate to write false affidavits. “My son’s class, 15 days, 1 positive case, 4 contact cases, I pretend to test him, I order him to say that he has been tested, sworn statement, and vaya con dios. (…) On the nerve now, no pity, “says a parent on Twitter.
My son’s class, 15 days, 1 positive case, 4 contact cases, I pretend to test him, I order him to say that he has been tested, sworn statement, and vaya con dios.
RAS, no return from school.
On the nerve now, no mercy.????????– pragmatus cynik (@ Stephaneheuzel1) January 14, 2022
A situation that exasperates teachers and unions. “We do not change a protocol to please the parents but to protect the children and adults present in the school. We want saliva tests distributed in schools like in Germany and Austria! “, got carried away Rodrigo Arenas, representative of the Federation of parents’ councils (FCPE).
We don’t change a #protocol to please the parents but to protect the children and adults present in the school! We want saliva tests distributed in schools like in Germany and Austria! #castex20h
– Rodrigo Arenas (@arenasfcpe) January 10, 2022
“We are in the process of investigating this file”
“Many parents are in favor of saliva tests, confirms Dr. Sylvie Hubinois, pediatrician and president of the French Association of Ambulatory Pediatrics (AFPA). There are children with whom screening would be much easier. If the data from this study is confirmed, it would make saliva testing a valuable tool.”
If these are only preliminary data, they are already being scrutinized by the French health authorities. “We are in the process of investigating this file, generating data to compare the effectiveness of the two methods”, indicated the Ministry of Health to the JDD.