what do the curves of the epidemic show, a week after the end of the restrictions?

A man takes a Covid-19 screening test near Nantes, October 15, 2021.

While the measures to fight against Covid-19 have been reduced since Monday March 14, the number of contaminations continues to increase for all age groups and in all regions, while the number of hospitalizations does not decrease. more. In its recent epidemiological point, Public Health France recommends maintaining barrier gestures, in particular to protect the most fragile.

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On contamination

After reaching a peak on January 24 with 567,851 positive samples in one day (and a weekly average of 365,000 daily cases), contaminations quickly decreased. But the pace of that decline has slowed since late February, and the lowest point was reached on March 3, with a seven-day average of 51,700 daily cases. Since then, the number of contaminations has started to rise again, rising from 51,800 to 86,000 per day on average between March 3 and March 18.

This rise in cases is also illustrated in schools: 3,184 classes were closed on Friday March 18, against 2,693 classes the previous week.

In other countries, such as England, we are also seeing a very rapid growth in the epidemic, two weeks ahead of France. Faced with the increase in contamination, Austria announced the return of the mask (FFP2) indoors from Wednesday and the tightening of the rules for isolating positive cases.

“European countries are seeing the first effects of the casualness of their policies vis-à-vis the management of the pandemic”has recently tweeted epidemiologist Antoine Flahault.

This is what the Institut Pasteur predicted in its models, published Thursday March 10, indicating that the epidemic rebound would largely depend on the degree of relaxation of barrier gestures and the multiplication of social contacts of the French. In its most pessimistic scenarios, where “transmission rates are increasing dramatically”the Institut Pasteur estimates that the peak of contamination “could exceed 100,000 daily cases in March”. This high figure remains “very much lower than the January peak”which had reached, at its peak, a rolling average of 365,000 daily cases.

Why such a difference ? Because the high level of circulation of the virus during the winter of 2021-2022 caused, from November 19, 2021 to March 3, approximately 16.15 million Covid-19 infections, which reduced the number of individuals n having no immune protection against the virus. From now on “80% of people” are vaccinated and “a significant proportion of the population has already been affected by the infectionunderlined Yazdan Yazdanpanah. This immunity, probably, protects us. At least in terms of hospitalizations. »

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In the hospital

The number of new hospitalizations has stabilized, and this is not necessarily good news. “For two days, the number of hospitalizations has not dropped”noted Monday the Minister of Health, Olivier Véran, in The Parisian. Between March 14 and March 20, the number of people admitted to hospital rose above 1,000 per day, on average. On March 20, 1,642 patients were in critical care for Covid-19.

“Hospital admissions have been increasing again for eight days and intensive care arrivals are more or less stable, as is the number of deaths. Which means it’s not going down anymore.worried epidemiologist Catherine Hill in The Express.

The level of hospitalization will certainly start rising again by following the contaminations, as it has done since the start of the epidemic, but it should remain limited if the number of new cases does not explode. “Our model does not quantify the impact on the hospital to anticipate in March, but it will probably remain absorbable”estimated Simon Cauchemez, researcher at the Institut Pasteur, in World, Thursday March 10.

If the public hospital can still absorb a new wave of hospitalizations due to Covid-19, weariness weighs on hospital staff, after two years and five epidemic waves which have drained its resources and postponed many care activities for decades. month.

“My fear is not so much what happens in the coming weeks, but more in the next six months”, explained Monday Rémi Salomon, president of the medical committee of establishment of the AP-HP, on RMC. Because, according to him, “The hospital is more fragile than before the pandemic, paradoxically. »

Without even counting the loss of opportunity for patients with serious illnesses, Covid-19 also results in a heavy human toll. Between November 19, 2021, when the circulation of the virus intensified significantly, and March 14, 2022, 21,939 people died from Covid-19, an average of nearly 190 per day. The fact that the less virulent Omicron variant replaced the Delta variant in January 2022 has reduced the number of deaths, but very slowly. The number of daily deaths (on a sliding average) has just fallen below the threshold of one hundred, on March 16, 2022. This had not happened since December 6, 2021.

On the effects and predominance of the BA.2 variant

According to Yazdan Yazdanpanah, the increase in the number of cases is linked to the “reopening of schools” after the holidays, to a probable “population slackening”, but also to the predominance of BA.2, one of the sub-variants of Omicron. According to the latest epidemiological update from Public Health France, the latter became the majority throughout mainland France in early March, with 52% of cases detected.

BA.2 is 30% more contagious than BA.1, another previously dominant Omicron sublineage, according to a Danish study. “The study shows that if a household is infected with BA.2, there is an overall 39% risk that another member of the household will be infected within the first week. This risk is 29% if the household is infected with BA.1”pointed out the Danish Infectious Diseases Control Authority.

This shortening could make future waves of contamination more “sudden”

Another point of concern linked to BA.2: its “serial interval”, that is to say the number of days between one infection and another in the chain of contamination, seems shorter than with its cousin Omicron. According to preliminary data published by Public Health England in its February 22 report, it would be 3.27 days compared to 3.72 days for Omicron. This shortening could make more “sudden” future waves of contamination. As an illustration, the influenza virus is not very contagious (its reproduction rate is 1.5 on average), but its serial interval of 3.6 days makes epidemics quite “explosive” : they rise very quickly but fall just as quickly.

Vaccine protection is not reduced by this new sub-variant, according to a study by the British Health Agency. With two doses of vaccine, the efficacy is 10% for BA.1 and 18% for BA.2. With three doses, the efficacy increases to 69% for BA.1 and 74% for BA.2, then falls to almost 50% two and a half months later for both. People who have not received any vaccine dose, on the other hand, would be more likely to be infected with this new variant, compared to BA.1.

Another reassuring point: BA.2 would not cause more serious cases than Omicron, still according to the British agency. Data adjusted according to age, previous infections, gender, or even ethnic origin, even suggest a lower risk of hospitalization and development of a severe form of the disease. However, these are early estimates and may change as data accumulates.

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The World Health Organization (WHO) Technical Advisory Group on the Evolution of the SARS-CoV-2 Virus also reviewed clinical severity data collected from South Africa, the United Kingdom and Denmark. He concludes that there was no reported difference in severity between BA.2 and BA.1. While it is possible to become infected with BA.2 after contracting BA.1, a person previously infected with Omicron remains “highly protected” against BA.2.

Public Health France informed that work was underway to more accurately estimate the transmissibility, severity and immune response escape of BA.2 compared to BA.1.

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