A number of contaminations which is on the rise again (+ 29% in one week), an incidence rate which goes back above the alert threshold in Paris… According to the latest figures of the covid in France, the virus is regaining ground and raise fears of the arrival of a fourth wave.

But what would it look like, now that more than half of French people have received at least one dose of the anti-covid vaccine?

A fourth wave from the end of July?

First question that arises: when could this wave arrive? If the experts ofPastor Institute estimated in June that the fourth wave could occur in the fall, the Minister of Health Olivier Véran now warns of a risk “from the end of July “.

A forecast based on the example of the United Kingdom in particular, where the Delta variant, more contagious than other strains of coronavirus, has led to a rapid increase in the number of cases.

In France, the proportion of this variant doubles every week, revealed on July 6 the government spokesman Gabriel Attal.

To read also: Risk of contamination, end of barrier gestures …? How to live once vaccinated with two doses?

Collective immunity is still a long way off

Vaccinating will not have served for nothing? On the contrary, it is the only weapon that could limit this wave. But for this, vaccination coverage must be maximum.

Today, nearly 35 million French people (51%) have received at least one dose and 24 million (36%) have a complete vaccination schedule. To achieve collective immunity, scientists estimate that 60 to 70% of the population must be fully vaccinated. By the time this figure is reached, an epidemic wave is therefore quite likely.

Unvaccinated youth more at risk

Particularly among those under 50 years of age, among whom vaccination rates are lowest. It is also in these age groups that Public health France observes the strongest changes in the incidence rate in recent weeks: + 66% for 20-29 year olds, + 23% for 30-39 year olds and 10-19 year olds and + 9% for 40-49 year olds . The over-50s, for their part, have stable, even declining, rates.

People affected by a fourth wave may therefore be younger people, unvaccinated or not fully vaccinated. Because, remember, the vaccine does not reach its maximum effectiveness until two weeks after the second dose.

The threat of new variants

Are vaccinees also likely to be affected? Yes, for several reasons. First, because no vaccine is 100% effective. The Pfizer vaccine, for example, is 95% effective, which means that on average, out of 100 people vaccinated, five may still be infected with covid.

Secondly, because certain variants, such as the Delta plus variant, could escape the surveillance of the immune system. This means that these variants are different enough from other strains of coronavirus that an organism that has been vaccinated (or immunized with infection) does not recognize it.

Fewer serious forms

The good news, however, is that vaccinated people who catch covid are still less at risk of developing severe forms of the disease. One of the characteristics of this fourth wave could therefore be a lower number of hospitalizations and deaths, even if the number of people positive for covid were high.

The elderly are still at risk

With one exception: the elderly, who are less well protected than a younger person. Indeed, the older we get, the less effective our immune system is. A study published on June 30 in the scientific journal Nature shows that even after two doses of anti-covid vaccine, the antibody level in people over 80 is lower than in people under 80.

The elderly, even vaccinated, therefore remain a high-risk population in the face of covid and in particular in the face of new variants. It is for this reason that the question of compulsory vaccination of nursing staff in nursing homes arises.