Debates on the extension of the health pass were agitated in the National Assembly this week, and some statements were more marked than others.
The president of the party "Debout la France" Nicolas Dupont-Aignan and the Insoumis François Ruffin, both deputies, suggested that the vaccine offered only individual protection against the serious forms and could not protect against the infection and transmission of the virus.
Truly ?
What you may have heard
"We were told that we had to be vaccinated out of altruism, to protect others, but it has now been shown that collective immunity does not work," exclaimed François Ruffin on Wednesday evening, while Nicolas Dupont- Aignan estimated that it is "the individual protection which counts for the vaccination and not a so-called
collective immunity
which all the scientific journals defeat! ". In his view, the vaccination of adolescents, who are little at risk of severe forms, is therefore “problematic” because of “the consequences of side effects”.
"We were told that we had to be vaccinated out of altruism, to protect others, but it has now been shown that collective immunity does not work," says @ Francois_Ruffin. # DirectAN #PasseSanitaire pic.twitter.com/ Lx3AJsJ425
- LCP (@LCP) October 20, 2021
Why is it excessive
When we talk about the effectiveness of vaccines on viral circulation, we must distinguish two things: the risk of being infected (if we have not caught the virus, we obviously cannot transmit it), and the risk of infection. be contagious if you are infected.
First point: effectiveness against infection. Regarding the two messenger RNA vaccines Pfizer and Moderna, which are almost the only ones administered in France today, it is quite high shortly after receiving two doses of the vaccine (around 90% or 80%). "If you have been vaccinated recently, the chances of developing a non-serious form of the disease and that of contaminating it are low," assures Professor Cyrille Cohen, immunologist at Bar-Ilan University (Tel Aviv) and member of the board. Advisory Committee on Clinical Trials of Covid-19 Vaccines.
However, this efficacy against infection declines markedly over time, generally reaching around 50 or 60% after five or six months, according to different studies.
Even 39%, according to data communicated at the end of July by the Israeli ministry of health.
What remains nonetheless not insignificant.
But it is true that protection against severe forms seems to be maintained at very high levels for at least several months.
Read alsoCovid-19: is post-infection immunity better than that after vaccination?
What if you are infected and vaccinated, can you spread the virus? Again, the answer is yes… but the risk is lower. More precisely, the Institut Pasteur estimates that it would be 50% less important. "We estimate that the contagiousness of a person infected but vaccinated is reduced by 40% compared to an unvaccinated person", indicates for his part Samuel Alizon, evolutionary biologist at the CNRS in Montpellier, whose modeling work has was pre-published at the end of August.
To explain it, we must in particular look at the side of the viral load. With the Delta variant, the US Centers for Disease Control and Prevention (CDC) reported this summer that it would be equivalent just after infection in the unvaccinated and vaccinated. But it would drop much more quickly, after five days, in people vaccinated, according to a preliminary Singaporean study posted online in early August. "The viral load is reduced more quickly in the nose, the virus will multiply less in the body and this limits contagiousness", summarizes Olivier Schwartz, head of the Virus and Immunity unit at the Institut Pasteur. “Certainly, we may have overestimated the ability of vaccines to control the circulation of the virus. But neither should it be underestimated ”,complete Samuel Alizon.
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However, the further away from the second injection, the more the vaccines seem less and less effective "to protect the others".
This makes it much more complicated to achieve collective immunity, that is to say to bet on high vaccination coverage to stop the epidemic, and would go in the direction of François Ruffin and Nicolas Dupont-Aignan.
"But there is still a certain protection that remains, and it is classic in vaccinology that it decreases over time", emphasizes Olivier Schwartz.
Towards a booster dose for all?
The purpose of the booster doses is precisely to give a “boost” to immunity.
Data published Thursday in the New England Journal of Medicine (NEJM) shows that antibody levels increase very sharply with a third dose of Pfizer vaccine.
While this does not imply that the protection against infection increases to the same extent, there is nevertheless a correlation and one can expect a real positive impact.
Based on a clinical trial conducted on more than 10,000 people aged 16 and over, Pfizer announced on Thursday that a booster dose (in this case a third dose) reduced by 96.5% the risk of symptomatic form compared to a control group having received "only" two doses.
Read alsoVaccination against Covid-19: will booster doses be required each year?
Real-life data in Israel seems to confirm that protection against simple infection is on the rise. For a population of equal size, there are now 10 times more positive cases in unvaccinated people than in those who received "only" two doses of vaccine (generally several months ago), and 20 times more in those not. vaccinated than in those who received a booster dose. "We can retort that vaccinated people are less tested, but I think that can not explain everything and the booster dose undoubtedly produces an effect," says Professor Cyrille Cohen. The two curves "unvaccinated" and "vaccinated without booster" were very close in recent weeks, which seems to attest to the decline in efficacy against infection.
For the moment, in France, only the elderly, suffering from comorbidities, and health professionals are called upon to receive a booster dose.
The High Authority for Health deemed it "probable" to soon widen the target to more or even all vaccinated adults.
But we still lack perspective when it comes to the balance between benefits and risks for young people.
In summary :
The effectiveness of vaccines against infection decreases over the months, but that does not mean that they no longer have any impact on the risk of becoming infected and transmitting the virus.
The booster vaccinations, which could be extended to the entire adult population in the medium term, aim to “boost” the immunity conferred by the vaccines.
