More and more rare are those to have passed between the droplets. Since the start of the year, nearly 9.2 million cases of Covid-19 have been detected in France. As many people, vaccinated or not, whose immune system has come into contact with the Sars-CoV-2 virus.
Fortunately, in most cases, infected people are asymptomatic or recover after a few days of symptoms of varying intensity. This is even more true with Omicron: having become the majority in the country during the winter, this variant is proportionally responsible for fewer visits to intensive care than Delta, its predecessor.
Are the millions of people who have contracted Covid-19 in recent weeks safe from a new infection? Is their immune system better armed against the virus than after a simple vaccination? Franceinfo asked these questions to specialists.
Let’s start with a little reminder: the vaccines currently authorized in France have been developed to teach our immune system to produce antibodies responsible for neutralizing the spicule (or Spike protein) of Sars-CoV-2, which plays the role of key to the virus entering the body. “Vaccination will cause our immune system to produce various antibodies, but all of which target different parts of the spike in order to prevent the virus from entering”, explains Sandrine Sarrazin, Inserm researcher at the Marseille-Luminy immunology center. When the virus enters the body, the immune system has more work to do.
“When you are infected, your immune system will react not only to the Spike protein, but also to all the other parts of the virus, such as other proteins of the viral envelope such as hemagglutinin-esterase or the protein Mr.”
Sandrine Sarrazin, Inserm researcher at the Marseille-Luminy immunology centerat franceinfo
Highly transmissible through aerosols, Sars-CoV-2 also challenges the airways during infection. This leads to an immune response complementary to that generated by the vaccine, says epidemiologist Yves Buisson. “The virus enters through the nose, throat, larynx, or bronchi. This entry route through the respiratory mucous membranes will cause a local immune reaction: specialized cells will produce mucosal antibodies there and provide protection against reinfection. by the same virus, completes the one who also chairs the Covid-19 cell of the National Academy of Medicine. Several researchers are also working on a vaccine in the form of a nasal spray, which would be able to block the entry of the virus through the respiratory tract.
Being infected with the coronavirus therefore causes our immune system to produce a more varied range of antibodies than after a vaccination. But voluntarily waiting to contract Covid-19 to escape vaccination would be a very risky calculation: the disease can leave persistent sequelae (we then speak of “long Covid”) and cause a runaway immune system potentially devastating for the body. (we then evoke a “cytokine storm” or a “Pims syndrome” in children).
To avoid these serious forms, current vaccines remain very effective. According to an American study pre-published at the end of November (in English)messenger RNA vaccines – like those from Pfizer-BioNTech and Moderna – have the advantage of causing the body to produce more antibodies than a simple infection (especially after a booster).
They also cause another immune response, which causes cells called T cells to recognize and destroy cells infected with Sars-CoV-2. “A study recently published in the journal Cell also shows that these T lymphocytes are able to recognize all variants, from Alpha to Omicron”notes Olivier Schwartz, head of the virus and immunity unit at the Institut Pasteur.
How long can the millions of people infected in recent weeks hope to be safe from further contamination? It’s still a bit early to know. In February 2021, the High Authority for Health estimated (PDF) that people whose immune system had reacted to a Covid-19 infection should “be considered protected for at least three months, but more likely six months”.
“After being sick, you are generally well protected against reinfection. The question will be how much protection will be in three months”confirms Claude-Agnès Reynaud, director of research and immunologist at the Institut Necker-Enfants Malades.
“During previous waves, it had been observed that antibodies remained present for more than a year after infection, even if their quantity gradually decreased.”
Olivier Schwartz, head of the virus and immunity unit at the Institut Pasteurat franceinfo
The duration of the immunity conferred by the infection will also depend on the emergence or not in the coming months of a new variant capable of escaping the immunity acquired in the past, like Omicron at the end of the year 2021. Due to a large number of mutations present on the Spike protein, this variant indeed succeeds in partially circumventing the protection conferred by a previous infection or by vaccines, which target the shape of the spike attached to the historical strain of Covid-19. It could thus be at the origin of the increase in suspicions of reinfections observed by the health authorities in the United Kingdom since mid-December.
Very interesting new data from England tonight.
In recent days, around one in ten new positive cases corresponded to a suspected reinfection (a person who tested positive for the first time at least 90 days ago). #Covid19 #Omicron pic.twitter.com/qOBrf8Yr82
— Nicolas Berrod (@nicolasberrod) January 31, 2022
Could this new variant that would shatter the immunity conferred by the millions of infections linked to Omicron be the BA.2 sub-variant? Asked Tuesday, January 25 on the set of LCI, the Minister of Health made this assumption. Olivier Véran thus noted that several cases of people having been infected by Omicron then by BA.2 had been identified in Denmark, a country where this sub-variant has become the majority.
“It is a risk that we consider, in part to understand why there is this increase in daily cases in Denmark. But it will take time to have data”again warns Etienne Simon-Loriere, head of the evolutionary genomics unit for RNA viruses at the Institut Pasteur, in the columns of the Parisian.
It remains to be seen whether the millions of people affected by Omicron in France in recent weeks are protected from the previous variants. The question arises in particular for Delta, which still circulates, although very weakly, on the territory. Scientific work is not unanimous on this subject: a pre-published study by South African researchers (in English) argues that infection with Omicron would enhance immunity against Delta, while American work (article in English)also in pre-publication, indicate that a former patient affected by Omicron will only see his immunity reinforced vis-à-vis Delta in the event of prior vaccination.