Once hoped to be “immunity passports” essential for safe deconfinement, serological tests do not ultimately play this first role. Despite everything, they have a real utility in the knowledge and control of the Covid-19 epidemic.
Their highly anticipated official appearance took place last week, with the announcement of their reimbursement by Social Security. But the health authorities confine themselves to a “complementary” role, in a few precise indications and on prescription, these blood tests which look for the presence of antibodies indicating if a person has been confronted with Covid-19.
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In question, the uncertainties that persist on the link between the presence of antibodies and protection against reinfection, and the fear that a wide use of these tests is a pretext for a “loosening” of precautions in the population.
“Performing the test only makes sense for people who have had symptoms or who, because of their profession, were particularly exposed to the coronavirus. This is particularly the case for nursing staff and staff working in nursing homes, ”insists the Ministry of Health, interviewed by AFP.
In the current state of knowledge on immunity associated with exposure to the virus, “it is not advisable to carry out this examination without medical accompaniment”, he adds.
However, on the ground, confusion persists on the place to give to this examination and on the interpretation to be made of the result.
These serological tests have already been carried out without a prescription for several weeks in many medical biology laboratories, and certain local authorities organize screening campaigns, such as the city of Nice, which will offer its inhabitants free serological screening on a voluntary basis. from Wednesday.
Unanswered questions
Some pharmacies also do this, even though they are not authorized for the moment.
Behind these initiatives, a real curiosity of the French: “I had a cough during confinement, was it the Covid?”, “I will see my grandchildren again, am I immune?”, “Can I return to work safely?”
“I understand these questions. But we can probably not generalize their use until we have more information on the correlation between antibody level and protection, and on the duration of protection, “explains AFP Christophe D’Enfert , scientific director of the Institut Pasteur, where the performance of approved tests was assessed.
“If a patient asks me, ‘Have I been in contact with the virus?’ Yes, I offer him the serological test. But if he asks me the question: “Am I immune?” Or “Am I contaminating?”, I tell him that I cannot answer … “, says Hikmat Chahine, director medical of the group of biological laboratories Unilabs.
This reasoning is all the more true in regions and environments little affected by the epidemic, because even tests whose performance is excellent see their “predictive value” decrease in a population where the disease is infrequent, it is that is, the probability that they give an incorrect answer is higher.
“Clarifying the doctrine”
“We must not play sorcerer’s apprentices, we must put each test in its place,” added the biologist, calling on the authorities to “clarify the doctrine”.
Scientific knowledge has progressed in recent weeks, notably with the publication in late May of a study by the Institut Pasteur which shows that even patients with minor forms develop antibodies and that these antibodies manage to neutralize the virus in the laboratory.
This study “settles the question”, judge François Blanchecotte, president of the Syndicate of biologists (SDB), estimating that the serological tests answer a real need to accompany the deconfinement of all those who work in community.
“But what will this information bring me on an individual basis?” Questions Professor Pierre Tattevin, infectious disease specialist at the Rennes University Hospital.
“If my serology is positive, does that allow me to go for a walk in the streets, in stores without a mask?” The answer is no. We don’t know enough yet, ”he warns.
In fact, “we still do not know formally whether this neutralizing activity is associated with protection against reinfection,” explains Professor Olivier Schwartz, head of the virus and immunity unit at Pasteur, to AFP.
In the meantime, the “precautionary principle” therefore prevails, all the more so that even if a positive serological test guaranteed the absence of personal risk, it would not however authorize lowering the guard.
“If you shake the hand of someone who is sick, even if you yourself do not get sick, you can then shake other hands or spread the virus on surfaces and thus contaminate other people”, warned the Minister of Health Olivier Véran.
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