Ten short days. It was the brief respite Sophie experienced between her two infections in COVID-19. He tested positive on February 3, negative four days later, decided to get tested again on February 14. “I felt very bad: shortness of breath, enormous tiredness, strong 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.
If since the beginning of the epidemic the possibility of contracting the virus was identified twice within a few weeks of each other (1), there have never been so many cases of reinfection. 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 Luminy immunology center in Marseille. 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 is almost like contracting two different viruses, first Sars-CoV-2 and then the flu. » The two infections may even be concomitant.. “Some people have had Delta and Omicron at the same time, generating a new virus at the same time: deltacron”, she remembers.
In recent weeks, others, rarer, have had the unpleasant surprise of being infected twice by Omicron, first by the BA1 subvariant, then by its “brother”, BA2. Annoying but logical, according to Yannick Simonin, a virologist at the University of Montpellier. « We knew from the beginning that the immunity conferred by Omicron is quite low, which is in a way the trade-off for a milder infection in general, he lifts Mostly in January, BA1 was supplanted by BA2, which created a kind of secondary 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 scratch”
And the vaccine in all this? Sophie had just done her encore when she first got covid. With a third dose and a recent infection on the clock, she thought she was “quiet for a while”.“The vaccine is still useful, since it still protects against severe forms”, insists Sandrine Sarrazin. However, the immunity it confers is no longer specific enough. “Vaccination provides antibodies directed against the original strain of the virus, the one from Wuhan. So the weapon no longer adapts to the target, a bit like attacking a tank with a crossbow.” she compares
→ DISCUSSION. Did Europe drop its guard too quickly against Covid?
Less effective vaccines, uncertain immunity… Enough to lose hope of a Covid-free life. “Obviously, you can get the feeling that it will never end, but you’re not starting from scratch, reassures Yannick Simonin. The global immunity acquired by infections and vaccination means that we are not in the same situation as two years ago. This achievement does exist, and if it does not protect from contagion, it protects us from serious forms and therefore from the risk of hospital saturation. As for the risk of being re-infected, it is still less important than that of being completely infected, especially if you do not have a complete vaccination schedule. »
The Bad Idea of Antibody Assays
In this context, some might be tempted to perform an antibody assay to assess their immunity. Bad idea, says Sandrine Sarrazin: “It happens that doctors prescribe serologies to their patients, in particular to evaluate the usefulness of a fourth dose. But today, we don’t know what level of antibodies is necessary to be protected. Above all, rates can drop very quickly. Therefore, this would involve dosing several times in a row to see if the level remains stable. »
For the researcher, the lack of hindsight on vaccines, often presented 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 ourselves 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. »
Cases remain low but hospitalizations rise
On Wednesday, April 6, contamination fell for the fifth consecutive day, with 161,950 new positive cases registered 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 in intensive care.
The incidence rate, although still high (more than 1,434 per 100,000 inhabitants), is beginning to decline in some departments.
Omicron accounts for 99.9% of sequenced tests, according to the latest Flash survey on March 14. The BA2 subvariant is largely responsible for 84% of detected cases, according to Public Health France.