If you have ever been infected with Covid, you have proof of this via a positive PCR test. In this case, a single dose of vaccine is sufficient to protect you from serious forms, whether you had the Covid 3 months or 1 year ago.
“The protection conferred by a single dose injected to a person with a history of infection is greater than that of the two doses injected into a person without a history of Covid. And this, regardless of the duration of the infection”, confirms Dominique Le Guludec, President of the College of the Haute Autorité de Santé, this June 3.
“This recommendation applies regardless of the age of the infection, people who have already been infected retain an immune memory”, underlines the HAS in an opinion published on June 3. When the infection has been diagnosed by PCR or antigen test, the HAS recommends carrying out the vaccination beyond 3 months after infection, considering that in this interval, people are protected by post-infectious immunity.
Corn pmaybe have you ever had the Covid without knowing it if you have made an asymptomatic form. In this case, a single dose of vaccine is also sufficient, provided … you know!
Serological tests before a vaccination: how does it work?
Since the end of June, the centers will be equipped with TROD, i.e. serological tests (blood) fast. Concretely: we prick the fingertip, after 10 to 15 minutes we detect or not the antibodies, if you have antibodies, it is because you had the Covid without knowing it, in this case, a single dose is enough to protect you.
As the vaccination is now open to teenagers, these tests will be offered from 12 years old.
In short, depending on the result of the serology, you will be told whether you need one or two doses.One way to speed up the campaign, by injecting only one dose to those with an asymptomatic infection. So to protect the population as a whole faster, “by vaccinating several million additional people more quickly in the niches and with the doses thus released, “underlines the HAS in its opinion.
The principle of serology: detecting the presence of antibodies
let’s remember that serology consists of detecting specific antibodies a pathology directly in the blood that appeared during a past infection. These antibodies then reflect the individual’s immunity. A virus protein is brought into contact with the patient’s blood; if there is a reaction, the patient has developed antibodies against the virus. For the coronavirus, it is whether a person has developed antibodies against the SARS-CoV-2 virus. Concretely, if the person has been sick or if they have already encountered the virus without developing symptoms.
3 types of serology: TROD, Elisa, TDR
There are three types of serological tests:
- The “Elisa” serological tests can be done in city laboratory by blood test (after centrifugation, the serum is analyzed).
- The blood rapid diagnostic tests (RDTs) are able to identify in 15 minutes, from a drop of blood taken from the fingertip, the antibodies produced by the body following an infection with the SARS-CoV-2 virus. The drop of blood is placed on a box, the strip of which changes color depending on the result. They are supposed to be offered in laboratories and pharmacies, but for the time being their access has not been recorded.
- Healthcare professionals (general practitioners, pharmacists, etc.) can also offer rapid diagnostic orientation tests (TROD). These tests consist, like RDTs, of taking a drop of blood from the fingertip. Results are available within minutes.
Where can we do a serology?
A Covid serological test can be performed in a pharmacy, laboratory or vaccination center.
- The so-called “Elisa” tests offered in the laboratory are more reliable than rapid serological tests (RDT and TROD). In fact, in the laboratory, the blood is centrifuged, which makes it possible to separate the serum (this is the blood freed from blood cells, such as gred lobules, white blood cells, platelets), the analysis is therefore finer.
- The so-called “TDR” tests that were to be offered in pharmacy, are still not.
- The so-called “TROD” tests have been offered since the end of June in vaccination centers, but also in pharmacies, as specified in Ministry of Health.
Serological tests: for whom?
“Serological TRODs are already available for purchase in pharmacies by everyone. However, as part of their free use in vaccination centers, serological TRODs are systematically offered to people. from 12 to 55 years old included“, indicates the Ministry of Health.
“People over 55 may also request to have a serological TROD performed at the time of the pre-vaccination interview in a vaccination center, doctor’s office or at home. It will be up to the health professional in charge of the pre-vaccination interview to decide whether or not to prescribe this TROD, in particular according to the patient’s state of health and his vulnerability to the disease “, underlines the ministry.
In addition, the HAS identifies 5 indications for serological tests, on medical prescription:
- The initial diagnosis of severe symptomatic hospitalized patients, in the event of a clinical picture or CT scan suggestive of SARS-CoV-2 infection and negative RT-PCR test
- The catch-up diagnosis of serious symptomatic patients hospitalized but who could not be the subject of an RT-PCR test for seven days
- The initial diagnosis of symptomatic patients without sign of seriousness followed in town in the event of a clinical picture suggestive of infection by SARS-CoV-2 and negative RT-PCR test
- The salvage diagnosis of patients with symptoms suggestive of SARS-CoV-2 infection (including prolonged symptoms of Covid-19) without signs of severity for whom an initial laboratory diagnosis has not been established.
On June 3, the HAS added an indication for TROD-type serological tests in the context of pre-vaccination screening. She therefore recommends offering them “during the first vaccination appointment to immunocompetent people (possessing the capacity to produce a normal immune response), without risk factors for developing a severe form of the disease (young adults before age 55) and without known or confirmed history of SARS-CoV-2 infection in order to determine their vaccination schedule “.
Conversely, serological tests are not relevant for the following indications:
- Initial diagnosis of a symptomatic patient with or without signs of severity for whom clinical examination and RT-PCR were performed during the first week after symptom onset and are consistent
- Testing of contacts of a confirmed or suspected patient
- Monitoring of patients with Covid-19; hospital entry or exit
- Systematic screening of occupational groups
- Screening in patients at risk of severe form of Covid-19
- Obtaining the health pass (the latter cannot be obtained on the basis of serology without vaccination)
- Monitoring of seropositivity (iterative tests)
Serological tests: price, prescription
In accordance with the nomenclature of biological acts, the prices were respectively set at 12.15 euros for the automated tests known as Elisa and at 9.45 euros for the rapid tests called RDT.
It is possible to perform a Covid serological test without prescription, as with any biological analysis.
What reliability?
There are doubts about the correlation between the presence of antibodies and immunity, in short, can you not catch the coronavirus twice? Be that as it may, the HAS calls for caution with regard to serological tests: “today, serological tests do not make it possible to rule on a potential protective immunity or a fortiori on its duration”.
The problem is also the interpretation of these tests. What to do with a positive result when we are not sure whether the presence of antibodies protects us, or for how long? In the end, the risk is to believe oneself protected and to relax the barrier gestures. Conversely, you can be tested “Covid negative” if you have been infected recently and have not had time to develop antibodies. What should be remembered is that the test can give rise to false positive or, conversely, false negative results.
Also read:
- All Anti-Covid Signal and Carnet: the health pass arrives on June 9
- How long does it take for the Pfizer vaccine to work?
- Can we transmit the Covid after being vaccinated?
- Covid-19: will vaccines (really) succeed in putting an end to the coronavirus epidemic?
- How to travel in Europe this summer?
- Covid vaccination certificate: how to get it?
