Contaminations and hospitalizations which are on the rise once more. More than two weeks following the lifting of health restrictions, France is at the heart of its sixth epidemic wave. In question: the BA.2 sub-lineage, now the majority. Mutated version of variant Omicron (BA.1), with an approximately 30% higher contagiousness, BA.2 contaminates massively.
If many people are affected despite a complete anti-Covid vaccination schedule, many reinfections are observed despite recent contamination. This raises the question of the immunity developed following an infection by Omicron. Are you protected once morest BA.2 when you have already contracted BA.1? Is the immunity acquired following infection protective, and for how long? Depending on the data collected, you may want to put your mask back inside.
Weaker immunity
As soon as it appeared in November, Omicron quickly revealed its specificities: a strain which causes fewer serious forms than the previous ones, but which presents an immune escape. Not only the Covid vaccines confer weaker immunity once morest it, but the immunity acquired following 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 might potentially recontaminate ourselves with BA.2 even when we have already been contaminated with Omicron”, advanced the Minister of Health, Olivier Véran, on LCI at the end of January. Thus, “the 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 reinfections with BA.2 following infection with BA.1 have been detected, they remain rare, which is an element in favor of cross-protection between the two sub-lineages”, reassures the health agency. .
But in practice, the numbers get carried away. “The incidence rate over the past seven days is 1,329 per 100,000 population, up 50% from the previous week. It even climbs to 1,895 among 10-19 year olds, currently among the most affected, with a positivity rate approaching 50%. And the reproduction rate of the virus, the famous R, is 1.3 “, details for 20 Minutes Dr François Blanchecotte, President of the union of biologists. A resumption of the circulation of the virus “which generated an increase in the volume of tests carried out by 30%, i.e. more than 3.8 million PCRs and antigens over 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 sub-variant represents “73%” of new contaminations, specifies Public Health France.
Shorter immunity, with rapid reinfections
Because the variants and sub-variants follow each other, but are not alike. Unlike previous strains, “BA.1 and BA.2 affect the upper airways, but not deep, 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, he underlines. We observe that certain populations, in particular young people, are affected once more and much more quickly. In practice, those who have recently contracted Omicron can be re-infected one to two months later, which means that the infection has not triggered long-lasting immunity in them”.
A finding confirmed by a study prepublished on the medRxiv platform, carried out on a sample of participants infected between November 22, 2021 and February 11, 2022 presenting two positive samples within an interval of 20 to 60 days. “Of 187 cases of reinfection, we identified 47 cases of BA.2 reinfections soon following a BA.1 infection, mainly in young unvaccinated people who developed a mild form that did not lead to hospitalization or death”, confirm the authors. They see it as “evidence that Omicron BA.2 reinfections occur soon following BA.1 infections.”
And “when we superimpose vaccination and incidence rate, we see that those who have a complete scheme are less affected than those who have not received a booster, namely young people”, notes 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 beginning to detect a new BA.3 sub-variant in sequencing”.
A health strategy to adapt
Faced with a virus that adapts, the health authorities plan in return to adapt their strategy. “Should France align itself 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. A possibility considered by the scientific Councilwhich is considering “expanding it to people aged 65 to 79, especially those with risk factors”.
For the time being, “the Scientific Council (…) underlines the importance of maintaining all the monitoring systems in place for the time being”, adds the body which advises the government. “Keeping the sequencing is very important,” says Dr. Blanchecotte. We must remain able to study the changes that occur on the strains in circulation. Only a few weeks ago, BA.2 accounted for only 2% of cases, as Delta few months ago. Before becoming a majority in less than three weeks. The Scientific Council, still him, “recommends nevertheless to undertake a reflection on the evolution of these tools in the medium and long term”, paving the way for an exit from massive screening.
To date, BA.2 is the majority in France and is also “worldwide”, indicates Public Health France. It represents 66% of the nearly 280,000 Omicron sequences, compared to 22% a month earlier.