COVID-19. Operation, reliability, cost … five questions about the pre-vaccine serology test

For the millions of French people who have already contracted Covid-19, one dose of the vaccine is enough to get them fully vaccinated. But due to the lack of symptoms, some people do not know that they are infected with the coronavirus, and therefore can do without revaccination. Serological testing can be a solution to this problem.

What is a serological test?

A serological test detects the presence of antibodies and confirms that the patient has already contracted the virus, even without symptoms.

On the other hand, serology is not a test for infection and does not allow you to know if a person is infected at any time with T.

When to do it

After getting the first shot, if you want to avoid a second injection without knowing if you’ve already been infected, your hopes are in vain. The Higher Health Authority (HAS) indicates that any serological test performed between two injections is useless because it is currently impossible to distinguish between antibodies resulting from infection and antibodies resulting from the injection of the first dose of vaccine.

Tests are currently being studied to distinguish general natural immunity from immunity to vaccines. These two immune responses are really not exactly identical. In case of infection, the virus multiplies in the body and within a few days infects different types of cells: the coronavirus completely presents itself to the immune system. The cells of the immune system learn to recognize all of its antigens, which triggers a complex immune response. During vaccination, the immune response depends on protein S, a surface protein of the virus that allows it to attach to and enter target cells.

While waiting for tests that can discriminate to emerge, it is imperative that you be anticipatory and serologic before you receive your first injection of vaccine.

Where to do it?

Serological tests are available at pharmacies and laboratories. The ones in pharmacies are made from a drop of blood taken from the tip of a finger, and in the laboratory it is a blood sample. They are more efficient and accurate.

HAS also recommended the deployment of rapid diagnostic orientation tests (TRODs) directly to vaccination centers, according to May 31st.

With this type of test, the result is available in less than a quarter of an hour. The test will then be performed immediately prior to the first dose and 15 minutes later, i.e. the expected monitoring time after vaccination, a result that indicates whether the person is already a carrier of antibodies against Sars-CoV-2 will be known. …

At two vaccination centers, the Hôtel Dieu in Paris and the Gerland center in Lyon, an experiment is being carried out without any commitment. At the end of the experiment, the Ministry of Health will decide whether to generalize the system at the national level in accordance with the wishes of HAS.

How many French people have suffered?

An estimated 23% of the French population have been infected with Covid-19, and only 8% have been detected by PCR or antigen test.

So 15% of French people will get a second dose when they don’t need it. HAS recalls that “the protection provided by a single dose given to a person with a history of infection is greater than the protection provided by two doses given to a person with no history, regardless of age of infection.”

How much does it cost ?

Serological tests are reimbursed by Social Security if they meet the indications defined by HAS:

  • initial diagnosis of symptomatic patients without signs of severity, which follows in the city, and patients with severe symptoms, hospitalized in case of a discrepancy between the clinical picture and the result of a virological test (by RT-PCR method)
  • catch-up diagnosis in symptomatic patients – severe and hospitalized or no signs of seriousness, followed by urban follow-up – who could not be virologically tested for seven days during which they are susceptible
  • diagnosis in symptomatic patients without signs of severity who have been clinically diagnosed but not virologically tested
  • detection of antibodies in healthcare workers and community staff (EHPAD, prisons, etc.) that are asymptomatic.

In general, a serological test is only reimbursed if it is aimed at diagnosing Covid-19. However, there is one exception: the pre-vaccination tests performed at the Gerland centers in Lyon and at the Hôtel Dieu in Paris are also free of charge. On the other hand, if you do a pharmacy or laboratory analysis before vaccination, it will be at your expense.

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