Ten short days. This is the brief respite experienced by Sophie between her two Covid infections. Tested positive on February 3, negative four days later, she decided to be tested again on February 14. “I felt very bad: difficulty breathing, enormous fatigue, heavy cough, stomach pain. I thought it was the flu. But no, it was still the Covid! Even the pharmacist couldn’t believe it,” says this literature student.
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If the possibility of catching the virus twice a few weeks apart (1) was identified from the start of the epidemic, never have cases of reinfection been so numerous. Of the 685,858 possible cases identified by Public Health France since March 2020, more than 95% have occurred since December 2021, when Omicron appeared.
Cases of reinfection on the rise since the appearance of Omicron
“Most of the people who have been infected twice in the last three months have been infected with two different variants, first Delta at the end of last year, and now Omicron”, explains Sandrine Sarrazin, Inserm researcher at the Marseille Luminy immunology center. In question, the very different profiles of these two “mutants”. “They are distinct enough that antibodies produced during Delta infection have difficulty recognizing Omicron, emphasizes the researcher. In fact, it’s almost like catching two different viruses, first Sars-CoV-2 and then the flu. » The two infections can even be concomitant. “Some people have had Delta and Omicron at the same time, generating a new virus at the same time: deltacron”, she recalls.
In recent weeks, others, more rare, have had the unpleasant surprise of being infected twice by Omicron, first by the BA1 sub-variant, then by its “brother”, BA2. Annoying but logical, according to Yannick Simonin, virologist at the University of Montpellier. « We knew very early on that the immunity conferred by Omicron is quite low, which is in a way the counterpart of an overall lighter infection, he raises. Majority in January, BA1 was supplanted by BA2, which created a kind of sub-wave. This is particularly visible in the UK, where a recent study showed that 10% of positive cases were due to reinfections. »
“We are not starting from zero”
And the vaccine in all this? Sophie had just done her encore when she first caught Covid. With a third dose and a recent infection on the clock, she thought she was “quiet for a while”.“The vaccine continues to be useful, as it still protects against severe forms,” insists Sandrine Sarrazin. However, the immunity it confers is no longer specific enough. “Vaccination provides antibodies directed towards the original strain of the virus, that of Wuhan. The weapon is therefore no longer adapted to the target, a bit like attacking a tank with a crossbow,” she compares.
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Less effective vaccines, uncertain immunity… Enough to lose hope of a life free of Covid. “Obviously, you can have the feeling that it will never end, but you are not starting from zero, reassures Yannick Simonin. The global immunity acquired by infections and vaccination mean that we are not in the same situation as two years ago. This achievement does exist, and if it does not protect against infections, it protects us from serious forms and therefore from the risk of hospital saturation. As for the risk of being reinfected, it remains less important than that of being infected altogether, especially if one does not have a complete vaccination schedule. »
The bad idea of antibody assays
In this context, some might be tempted to do an antibody assay to assess their immunity. Bad idea, says Sandrine Sarrazin: “It happens that doctors prescribe serology to their patients, in particular to assess the usefulness of a fourth dose. But today, we do not know what level of antibodies is necessary to be protected. Above all, rates can drop very quickly. This would therefore involve doing a dosage several times in a row to see if the level remains stable. »
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For the researcher, the lack of hindsight on vaccines, often put forward by her opponents, is actually less dangerous than the lack of hindsight on the virus itself. “It only appeared two years ago and we still know little about its consequences. Contaminating yourself massively as we have done since the lifting of restrictions means running the risk of multiplying the cases of “Covid long”. And one thing is certain: this public health problem is before us. »
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Cases still down but hospitalizations up
Wednesday, April 6, contaminations were down for the fifth consecutive day, with 161,950 new positive cases recorded in twenty-four hours, a decrease of 4% in one week.
More than 23,000 people were hospitalized on Wednesday, that’s 164 more in one day. Among them, 1,561 are staying in intensive care.
The incidence rate, although still high (more than 1,434 per 100,000 inhabitants), is beginning to decrease in some departments.
Omicron accounts for 99.9% of tests sequenced, according to the latest Flash survey from March 14. Largely in the majority, the BA2 sub-variant is responsible for 84% of the cases detected, according to Public Health France.