Covid-19: what could the fourth epidemic wave that scientists fear bring together?

The trajectory of this epidemic rebound could vary according to the proportion of French people vaccinated, believe researchers from the Pasteur Institute.

To the question “is there going to be a fourth wave?” Professor Jean-Fran├žois Delfraissy answers “yes”, resigned. The president of the Scientific Council, used to commenting on the trajectory of the epidemic since the spring of 2020 wants to be clear, Wednesday, June 30, at the microphone of France Inter: the French may want to believe in the end of the epidemic, the Covid- 19 could come back in full force once the summer is over.

As proof, epidemiologists are keeping an eye on the United Kingdom, Russia and Israel, faced with an epidemic resurgence. However, vaccination campaigns in the United Kingdom and Israel are more advanced than in France. Respectively 65.48% and 64.14% of the population are vaccinated there, according to data from Our World in Data of June 27 (and only 14.81% in Russia).

An epidemic rebound under the threat of the Delta variant
If the incidence rate and the number of new contaminations in France are encouraging and even “extremely low”, according to Jean-Fran├žois Delfraissy, these figures are “in some ways falsely reassuring”, he assures us. Because summer is coming and will inevitably be a game changer. “We must remember what happened last summer. We were at roughly comparable figures, and we saw the second wave in September,” he recalls. The beautiful season could once again lead to a relaxation of barrier gestures, an increase in the movement of people and end at the start of the school year with a spread of the virus in schools, point out the scientists.

A newcomer could make matters worse: the Delta variant. Identified in India, this variant of the Sars-CoV-2 virus would be 40 to 60% more contaminating than the Alpha variant, detected in the United Kingdom at the end of 2020 and responsible for the third epidemic wave crossed by France. This worrying variant is already gaining ground in France: it now represents 20% of new diagnoses, or double the previous week, said the Minister of Health on Tuesday on franceinfo. By the end of August, it could concern “80-90% of contaminations,” said Arnaud Fontanet, research director at the Institut Pasteur, on BFMTV on Wednesday.

The strength of the rebound will depend on the vaccination
However, a new factor will influence the epidemic trajectory: vaccination against Covid-19. Unlike 2020, the one that comes begins when a little more than half of the French have received at least one injection of the vaccine against Covid-19 and that nearly a third of the population is fully vaccinated.

This is not enough, warn scientists. A “possible epidemic rebound this fall” remains probable according to a pre-published study (in English) from the Pasteur Institute, made public on Monday. If the vaccines from Pfizer and AstraZeneca remain effective after two doses against severe forms of Covid-19, the rate of fully vaccinated people remains insufficient to prevent an epidemic resumption. According to the authors of the study, the unvaccinated are twelve times more likely to transmit the virus than a vaccinated person. The more there are, the more the epidemic will be important.

Author: admin