A cotton swab stuck so deep in the nostril that it can have the unpleasant sensation of tickling the brain? Or a sample of saliva under the tongue or a simple spit in a tube? The prospect of swapping the nasopharyngeal test for a saliva test to detect SARS-CoV-2 is attractive. Much less invasive, faster, it would test more people.
Abroad, like in the United States or Japan, this method is already used. Many French people are therefore impatient and wonder why the saliva tests have still not been validated in the country, which is still at the stage of clinical trials. At the end of July, the Minister of Health Olivier Véran had even increased the pressure on the officials of the Public Assistance of the Hospitals of Paris (AP-HP) so that they accelerate on the saliva tests.
A whole new technology
However, researchers have been working for several months. “The epidemic started in our area in early February. The National Research Agency quickly made a call for projects and received proposals for studies on saliva tests. Tests were launched in March, but it takes time! »Recalls Anne Goffard, virologist and teacher at the Faculty of Pharmacy in Lille.
PCR tests by nasopharyngeal swab for Covid-19 were quickly deployed because this technique was already traditionally used for the search for respiratory viruses, including coronaviruses. “The nasopharyngeal smear was therefore used but, before this epidemic, we never needed to do 600,000 weekly tests. As it is not very pleasant, we are trying to develop other sampling methods, ”explains Yves Gaudin, virologist and research director at CNRS.
Once this nasopharyngeal PCR test had been developed, the researchers were able to focus on screening by saliva sample. "We needed a reference, now we can compare the tests", develops Dominique Le Guludec, president of the High Authority for Health (HAS).
Several methodologies under study
So far, the published scientific data does not allow the HAS to validate these new tests, which are deemed not to be reliable enough and generate many false negatives. “The virus does not seem to be present in saliva all the time. In some symptomatic people, it entered more deeply into the body, which was also a problem for the nasopharyngeal test, ”explains Yves Gaudin.
Also, the biological fluid in saliva is not the same as that in nasal mucus. “In the saliva, there are enzymes that can inhibit the PCR reaction” and therefore distort the analysis, adds Anne Goffard.
Other screening methodologies on saliva samples are being studied. Instead of the PCR technique (looking for the virus's RNA), scientists are trying to detect the SARS-CoV-2 antigen (the proteins that constitute it) in saliva.
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This method has the advantage of being much faster: the result is known in fifteen, twenty minutes. But it also presents difficulties: “During an infection, there is a smaller quantity of antigens than of RNA. "
The constitution of a "salivothèque"
In order to speed up research and collect "the missing data", "the HAS has issued a favorable opinion on the implementation of an innovation package for virological tests on saliva samples", announced the health authority on August 10. A comparative study has thus started in Guyana and the analysis of the withdrawals will be financially supported within the framework of this fixed price.
This vast trial is being carried out in Cayenne because "this is where there are the most patients, which will allow results to be obtained more quickly", indicates Dominique Le Guludec. It must include 1200 people who will be divided by age group into four groups.
The saliva samples will be kept in a “saliva library” which will contain the clinical data of each patient. “This tool will be very useful. The samples can be used to test other methodologies. We will save a lot of time, ”said the president of the HAS.
The High Authority for Health hopes to obtain the first results "early, mid-September". If the data are positive, "she will be able to trigger the evaluation process for generalized care, in the indications that she has defined".
AP-HP promoter of a real-life trial
In addition, the AP-HP will promote a trial consisting in evaluating in real life, and not in the hospital, various saliva tests.
"The research protocols will be sent in the coming hours for agreement to the ANSM, the Committee for the protection of persons and the Cnil", announced the institution to us on Thursday. The study could start in September.