Protection, reinfection… What immunity develops after contamination by Omicron?

Contamination and hospitalizations that increase again. More than two weeks after the lifting of health restrictions, France is at the center of its sixth wave epidemic. In question: the BA.2 sublineage, now majority. mutated version of Omicron variant (BA.1), with a contagiousness approximately 30% higher, BA.2 contaminates massively.

If many people are affected despite a full anti-Covid vaccination schedule, many reinfections are observed despite recent contamination. This raises the question of the immunity developed after an Omicron infection. Are you protected against BA.2 when you have already contracted BA.1? Is immunity acquired after infection protective and for how long? Depending on the data collected, you may want to put the mask back on.

weaker immunity

As soon as it appeared in November, Omicron quickly revealed its specifics: a strain that causes fewer severe forms than the previous ones, but that presents an immune leak. not only the Vaccines for COVID-19 would confer weaker immunity against it, but the immunity acquired after contamination by Omicron would also be of low quality, even in people with a complete vaccination schedule, according to a study recently published in the journal Cell. The researchers found that infection with the Delta variant, which generally causes a more severe clinical picture, produced antibody levels 10.8 times higher than with Omicron.

Consequence: “We could potentially recontaminate ourselves with BA.2 even when we have already contaminated ourselves with Omicron”, announced the Minister of Health, Olivier Véran, in LCI at the end of January. Therefore, “escape from the immune response is associated with higher rates of reinfection with Omicron than for previously circulating variants,” confirmed Public Health France on March 23. However, “if BA.2 reinfections have been detected after BA.1 infection, they are still rare, which is an element in favor of cross-protection between the two sublineages,” says the health agency.

But in practice, the numbers get carried away. “The incidence rate in the last seven days is 1,329 per 100,000 inhabitants, 50% more than the previous week. It even rises to 1,895 between 10-19 years old, currently among the most affected, with a positivity rate close to 50%. And the reproduction rate of the virus, the famous R, is 1.3”, he details for 20 minutes Dr François Blanchecotte, President of the biologists union. A resumption of the circulation of the virus “which generated an increase in the volume of tests carried out by 30%, that is, more than 3.8 million PCRs and antigens in the last seven days, which is considerable. And among the positive cases, there is a significant proportion of reinfections by BA.2”, continues the biologist. The subvariant represents “73%” of new contaminations, specifies Public Health France.

Shorter immunity, with rapid reinfections

Because the variants and subvariants follow one another, but they are not the same. Unlike the previous strains, “BA.1 and BA.2 affect the upper respiratory tract, but not in depth, and generate a severe cold, with conventional hospitalizations, certainly on the rise, but not in intensive care,” describes Dr. .Blanchecotte. Less serious forms, “but faster reinfections”, she emphasizes. We see certain populations, particularly young people, being affected again and much more quickly. In practice, those who have recently contracted Omicron can be infected again one or two months later, which means that the infection has not triggered long-lasting immunity.”

Finding confirmed by a study pre-published on the medRxiv platform, carried out on a sample of participants infected between November 22, 2021 and February 11, 2022 presenting two positive samples in an interval of 20 to 60 days. “Of 187 cases of reinfection, we identified 47 cases of BA.2 reinfection shortly after a BA.1 infection, mainly in young, unvaccinated people who developed a mild form that did not lead to hospitalization or death,” the authors confirm. They see it as “evidence that Omicron BA.2 reinfections occur shortly after BA.1 infections.”

And “when we superimpose vaccination and incidence rate, we see that those who have a full schedule are less affected than those who have not received a booster, that is, the young,” says Dr. Blanchecotte. At the same time, “the virus continues to mutate and adapt according to the individuals in which it can multiply”, recalls Dr. Blanchecotte. We are starting to detect a new BA.3 subvariant in sequencing.”

A health strategy to adapt

Faced with a virus that adapts, the health authorities are considering adapting their strategy in return. “Should France align with Spain, which no longer tests and lets the virus spread among the population? In which case, do we generalize the fourth dose to everyone over 60? asks Dr. Blanchecotte. One possibility considered by scientific councilthat it is proposed “to extend it to people aged 65 to 79, especially those with risk factors”.

For now, “the Scientific Council (…) underlines the importance of maintaining all monitoring systems for the time being,” adds the body that advises the Government. “Maintaining sequencing is very important,” says Dr. Blanchecotte. We must continue to be able to study the changes that occur in the tensions in circulation. Just a few weeks ago, BA.2 represented only 2% of cases, as Delta Some months ago. Before becoming a majority in less than three weeks. The Scientific Council, still he, “recommends, however, to undertake a reflection on the evolution of these tools in the medium and long term”, paving the way for an exit from mass screening.

To date, BA.2 is the majority in France and is also “worldwide”, indicates Public Health France. It represents 66% of Omicron’s nearly 280,000 sequences, compared to 22% the previous month.

Leave a Comment