A 4th wave of Covid-19 at the start of the school year? It all depends on vaccination, for the Institut Pasteur

published on Tuesday, June 29, 2021 at 5:18 p.m.

The evolution of the Covid-19 epidemic in the coming months will depend on the measures taken and the vaccination campaign, believe researchers from the Institut Pasteur. “An unvaccinated person has 12 times more risk of transmitting Covid-19 than a vaccinated person”, they assure in particular.

While life is resuming more and more normally, with in particular the last phase of deconfinement which begins on Wednesday, the Covid-19 crisis is far from over, warn the researchers.

At the beginning of the month, Professor Jean-François Delfraissy was counting on a relatively quiet summer before a possible recovery at the start of the school year. A possible hypothesis, also estimates the Pasteur Institute.

While the Delta variant is progressing inexorably in France, the Pasteur Institute published on Monday June 28 an update of its work on modeling the dynamics of the epidemic in France. The baseline scenario is as follows: an “R0” (the number of people that an infected individual will infect on average without any control measures) of 4, an efficacy of vaccines against hospitalizations of 95% and complete vaccination coverage 30% of 12-17 year olds, 70% of 18-59 year olds and 90% of over 60s.

In that case, “a peak in hospitalizations comparable to the peak in autumn 2020 could be observed in the absence of control measures”, or more than 2,500 per day, write the scientists. “A certain level of control of the epidemic may therefore be necessary this fall”, they assure.

Unvaccinated people would contribute “disproportionately to transmission,” the scientists say. “An unvaccinated person is 12 times more likely to transmit Covid-19 than a vaccinated person”, they say. The unvaccinated over 60 years would represent 3% of the population but 35% of hospitalizations, they estimate.

“The situation of children and adolescents, who should receive little immunization this fall, is a source of concern,” the researchers also write. According to the baseline scenario, they represent half of infections and are the cause of half of contaminations.

Less restrictions thanks to vaccination

To avoid such a situation, the Institut Pasteur considers that certain measures should continue to be applied and insists on the importance of vaccination. Today, their forecasts are far from being reached: 70% of those over 60 are currently vaccinated and 12.8% of those aged 18-59. The government is targeting the goal of 35 million French people fully vaccinated by the end of August.

If the vaccination campaign continues effectively, there should be no need to go as far as containment. “It is a message of hope: thanks to the vaccination, the necessary effort will not be as important as what we have known,” said the Parisian Simon Cauchemez, lead author of the study.

Testing half of people aged 12 and over who have not been vaccinated each week could reduce the peak of daily hospitalizations by 27% (with self-tests) or 32% (with tests done by professionals). Physical distancing or wearing a mask would also have a significant impact. If vaccination coverage climbs to 90% among 18-59 year olds, the peak of daily hospitalizations would rather be around 1,000. We can manage to limit the transmission of Covid-19 “by respecting barrier gestures, continuing to pay a little attention, to wear the mask in certain situations …”, assures Simon Cauchemez.

The Institut Pasteur also highlights a point that could convince the French to get vaccinated: the results would be almost the same if these restrictions only applied to unvaccinated people. “This suggests that, in a partially vaccinated population, control measures targeting unvaccinated people (for example with the health pass) could maximize control of the epidemic while minimizing the cost to society,” believe Researchers. “This nevertheless raises ethical and social questions that it is important to explore,” they stress.

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