A serological test can tell if you have contracted the coronavirus and if you are immune to the disease. - CATHERINE KOHLER / SIPA

  • Serological tests can determine if you have been in contact with the coronavirus and if you have developed antibodies.
  • From now on, it is possible to be prescribed by your doctor a blood test, but according to criteria determined by the Ministry of Health.
  • If these blood tests have a certain individual interest, their collective interest remains to be demonstrated.

They were to be a major tool in the deconfinement strategy. Thanks to serological tests, immunized people could have obtained an "immunity passport". But that was before the Institut Pasteur released its estimates at the end of April, according to which around 5.7% of the French population had contracted Covid-19 by the end of the confinement. Since then, the hope of collective immunity has evaporated and this tool has lost some of its interest. However, serological tests are far from useless.

On May 28, the government announced reimbursement by Social Security of these blood tests, which look for the presence of antibodies indicating whether a person has been exposed to Covid-19. But provided they have been prescribed by a doctor. But what are the criteria for taking charge? What is the point of these tests? And what risks do they entail?

"I want to know if I have had Covid-19 and if I am immune"

“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.

Marine, who works in a municipal nursery in Ile-de-France, awaits the result of her serological test, which is taken care of for all of her colleagues. “I had symptoms of the coronavirus at the start of confinement. Since then, I ask myself the question of whether or not I contracted the disease, so I am very happy that my job takes care of the test, says the young woman. I want to know if I have had Covid-19 and if I am immune. I almost hope that the result is positive, to feel more calm. Here, of course, all the staff wear a mask, but physical distance is impossible and we take care of babies! We no longer give them kisses, but we always have them in our arms, we play with them, we change them. It is important to take this test to be sure that I do not represent a risk for myself, for the little ones and for my colleagues ”.

"I have no reason to refuse the test"

Like Marine, many people want to know. "I understand these questions, but we can probably not generalize their use until we have more information on the correlation between level of antibody and protection, and on the duration of protection", explains Pr Christophe D'Enfert, Scientific Director of the Institut Pasteur, where the performance of tests approved and paid for by Health Insurance was assessed.

"Curiously, quite a few patients come to consult me ​​to be prescribed a serological test," notes Dr. Jacques Battistoni, general practitioner and president of the MG France union. Obviously, if a patient consults me because he thinks he has had the symptoms of the coronavirus and wants to know with certainty if he has had it, I have no reason to refuse it. Many are in this case, with some of the risks of sequelae, in particular respiratory damage, pulmonary fibrosis ”. For the past few weeks, many people have been complaining of persistent symptoms. For them, who developed symptoms compatible with the coronavirus in March, a period when tests - PCR or serological - were little practiced, the need to remove uncertainty is more and more felt.

Precise reimbursement criteria

And they would be entitled to be prescribed, according to the specific reimbursement criteria established by the ministry. “To confirm the fact that a person is infected, as soon as he presents symptoms, but that a first test by PCR was negative. Serological tests then intervene in addition to diagnosis, ”says avenue de Ségur. The test will also be reimbursed if it is prescribed "after the fact, when the person no longer has any symptoms and has never been tested positive by PCR, to confirm that he has been infected with the virus and thus allow, for example, to avoid further complications ”.

It is also covered "for health personnel or those who work in a medical or medico-social structure, taking into account the particular exposure to the virus which may have been their own and the fact that they intervene in contact with people fragile ”, indicates the Ministry of Health. "In addition, serological tests are useful for caregivers, especially for the recognition of Covid-19 as an occupational disease," adds Dr Battistoni.

Precautionary principle and barrier actions despite everything

But even if the result is positive, is it safe to be effectively immunized? Doubts about the effect and duration of the antibodies were quickly expressed by the researchers. But scientific knowledge has progressed in recent weeks. At the end of May, a study by the Institut Pasteur carried out among hospital staff at the two Strasbourg University Hospital sites showed that even patients with minor forms developed antibodies and that these antibodies managed to neutralize the virus in the laboratory. But "we still do not know formally whether this neutralizing activity is associated with protection against reinfection," said Professor Schwartz, head of the virus and immunity unit at the Institut Pasteur.

When in doubt, the precautionary principle is in order, especially since even if a positive serological test guaranteed the absence of personal risk, it does not authorize to lower 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.

A collective interest to demonstrate

Awaited by many patients, serological tests are struggling to demonstrate their collective interest. "They have an individual interest in satisfied curiosity, but beyond that, they do not lead to practical measures, therefore do not present any real collective interest," considers Dr. Battistoni. This would be the case if serological studies were carried out for epidemiological purposes, in given geographical areas, and on samples statistically representative of the population, he suggests. However, I have the impression that this is not the case today, which surprises me. At the beginning of May, shortly before the deconfinement, I asked the Scientific Council on the question of the strategy for the use of serological tests, to find out if a national policy was going to be put in place. I feel like we never really knew what to do with these tests. There is a lack of in-depth reflection on diagnostic tools and their optimal use. So we don't do anything about it, we let the patients self-prescribe the serological test in a way. And that's all ".

For the general practitioner, "extensive screening to assess the prevalence of coronavirus in the population would be very interesting". On the model of the epidemiological study carried out by the Pasteur Institute in Crépy-en-Valois (Oise), one of the first French epidemic foci of Covid-19.

An extensive epidemiological study has just been launched by the city of Nice (Alpes-Maritimes), which offers 18,000 volunteers a free blood test.

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