Massive screening in schools: when will rapid saliva tests be expected?

A swab in the nostrils? “It’s dead, I no longer set foot in high school,” comments a user. “Hands off my nose,” says another, as the government has announced massive screening in schools, using antigen tests and on a voluntary basis. How many, on the other hand, would accept the exercise if it was enough to spit in a tube? Saliva tests must be deployed without delay, so doctors are asking.

“We don’t really see how we’re going to do a million nasopharyngeal tests per month ( Editor’s note: the objective desired by the government ), with which caregivers? “Asks immuno-oncology researcher Eric Billy, member of the Du Côté de la Science collective. Much less invasive than nasal swabs, saliva tests would be more accepted by the population and “would thus make it possible to regain control over the epidemic”, he judges.

The government follows the advice of the HAS

Two types of saliva sample screening are currently covered by Social Security. Tests analyzed by the RT-PCR technique and those that use the integrated RT-Lamp method, such as EasyCov. But the High Authority for Health recommends their use only to symptomatic patients, and this when the nasopharyngeal sample is “impossible or difficult to perform”. A recommendation incompatible with massive screening.

The government, which follows the advice of the HAS, “is studying all the means that could make it possible to screen as effectively as possible, but we are moving forward according to the results brought to our attention”, recalls the General Directorate of health (DGS).

Is the saliva sample screening not reliable enough? False, replies Eric Billy, citing the example of EasyCov, which “discriminates between positives and negatives in the same way as PCR”, he says.

Too many false positives for EasyCov, according to HAS

This integrated RT-Lamp test, developed in Montpellier by the Skillcell and Vogo companies, in cooperation with the CNRS, has many advantages. Its result is obtained in about forty minutes, compared to several hours for an analysis by RT-PCR. It is easy to read: the test turns yellow if it is positive, orange if it is negative. Its cost, lower than for screening by PCR, is equivalent to an antigen test. Finally, it can be practiced alone and therefore does not require nursing staff, unlike nasal sampling.

While it is sold elsewhere in Europe, particularly in Belgium and Italy, as well as in Africa, the High Authority for Health remains cautious. To fully authorize a detection test for SARS-CoV-2, the institution requires a minimum “sensitivity” greater than 80% – the ability to correctly detect a positive case – and a minimum “specificity” of 99% – either the ability to correctly detect a negative case.

In the case of EasyCov, the HAS notes a “satisfactory” sensitivity, at 84%, in symptomatic people. On the other hand, it estimates its specificity at 92%, “below the minimum required performance”. There would therefore be 8% false positives with this test. “The poorer specificity requires carrying out a control by an RT-PCR test on saliva sample in the event of a positive test”, recommends the institution accordingly. And to add that “the absence of robust clinical data in asymptomatic people does not allow to recommend it, at this stage, in this situation”.

Different numbers

The analysis of the study conducted by SkillCell gives it a different specificity and in the standards, at “99.5%”, indicates Franck Molina, director of research in biology at the CNRS, at the head of the Sys2Diag laboratory which has developed EasyCov.

Why do the study numbers differ? By the evaluation reference of a test. “The HAS compared apples to oranges”, annoys Eric Billy. “If a patient was detected positive by RT-PCR, regardless of the sample (nasopharyngeal or salivary), it was recorded as positive. While the HAS only counted it in the positive if the nasopharyngeal sample indicated it as such, ”explains Franck Molina.

The High Authority for Health “therefore set aside certain data” and the number of patients included in the clinical study was reduced, says the researcher. “This is why she says she does not have sufficient data on asymptomatic patients,” he regrets.

A group of experts will meet

But the recommendations of the HAS are not set in stone. “A working group will meet next week to analyze the latest data published on saliva tests and potentially update previous opinions,” the institution tells us.

“We are working with the High Authority for Health on additional studies,” adds Franck Molina, who says he is “serene” for the future.