Why France needs to vaccinate 90 percent of adults to return to “normal” life

A new study published this week by the French Pasteur Institute concludes that as the British variant of Covid-19 is now dominant in France, as many as 90 percent of adults will need to be vaccinated before the country can return to its normal life without risking a new one. the increase in the virus.

According to a new modeling released on Tuesday on the Pasteur Institute’s website, the spread of the British variant in France has put a clear damper on the prospect of returning to life, as we knew it was a pre-pandemic this autumn, the horizon that some researchers had set only months ago.

The authors of the study conclude that since the British variant, known as B.1.1.7, now dominates other coronavirus strains in France, 90 percent of the country’s adult population would need to be vaccinated by the end of the summer before French residents can refrain from social distancing measures without causing a new increase in cases.

The effect of the British variant

The high level of vaccination among adults is a very high order in the infamous vaccine-skeptical France, where recurring delivery delays have further plagued the country’s initially sluggish vaccination. Specialists tell Jowharthat the 90% target would be virtually impossible to achieve.

“The main message of our work is that vaccinations enable us to emerge from the crisis, but we must expect to live with some limitations in the autumn,” said Pascal Crépey, co-author of the study and researcher in epidemiology and biostatistics at France’s EHESP School of Public Health in Rennes, told FRANCE 24.

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So how did the researchers arrive at the 90 percent figure when the generally accepted target until recently was a 60-70 percent protection level would offer the much-discussed levels of “crew immunity” needed to stifle Covid-19?

The answer lies in how thoroughly B.1.1.7 has raised the stakes. Specifically, the question is its effect on what is called R0 (pronounced R-nothing or R-zero), the rate of reproduction that determines how transmissible a virus is in terms of how many people an individual infected individual will infect on average. If R0 is less than 1, each infected person infects at most another individual and the infection rates would eventually decrease.

“R0 for the majority strain circulating in France has changed. It was about 3 for the original new coronavirus and it is estimated at between 4 and 5 for the ‘British’ variant,” Amaury Lambert, a professor of mathematics at Paris Sorbonne University, told FRANCE 24.

The jump in R0 was calculated “taking into account the scientific estimates according to which the British variant multiplies 60 percent more easily”, said Crépey.

Vaccinating children helps everyone

On that basis, the increased R0 “automatically increases the vaccination threshold needed to imagine a return to normal life without risking a new epidemic,” Lambert said. Hence the 90% figure given for inoculation of individuals over 18 years of age given the dominance of the B.1.1.7 strain in France.

However, researchers realize that the necessary threshold would not be as high if children were also vaccinated. In fact, “if only adults are vaccinated, a significant epidemic in children is still expected, contributing to the infection of unprotected parents and grandparents,” the authors of the Pasteur study state.

By including candidates under the age of 18, “vaccination between 60 and 69 percent of 0 to 64-year-olds and 90 percent of those over the age of 65 can enable a complete slowdown in control measures” as early as September, the authors suggest.

However, that discussion remains purely theoretical, as “no vaccine has been granted a marketing authorization for children in France”, Crépey stated. In fact, the results of clinical trials showing the Moderna, BioNTech / Pfizer and AstraZeneca vaccines are as safe and effective for minors as for adults have not yet been published. “Obviously, if we knew the effectiveness of these vaccines in children, this would make it possible to adapt the vaccination strategy,” said epidemiology specialist Jean-Stéphane Dhersin, Scientific Deputy Director of the French National Institute of Mathematical Sciences, FRANCE 24.

Another parameter that can affect the priorities of the vaccination campaign is the level of protection provided by the injections. “At first we knew that the vaccines greatly reduced the number of serious Covid-19 cases, but we lacked the information to know if they were also effective in limiting transmission (infectivity) or in preventing the infection in the vaccinated person (susceptibility. priority would be to vaccinate vulnerable and elderly populations to limit the number of deaths and hospital stays, “Crépey explained.

Researchers have since been able to review data from Covid-19 vaccination campaigns around the world that suggest that available vaccines provide good protection against the risk of infection. The model maintained in the Pasteur study indicates that in the case of a vaccine that is effective both in preventing serious cases and in protecting against infection, “the order of priority for the populations to be vaccinated becomes less important,” Crépey pointed out.

In other words, extending vaccination to the entire adult population provides the same benefits – limiting the number of deaths and hospital stays – as well as prioritizing vaccination of the most at-risk populations.

“In fact, the vaccination of younger people, who have a lower risk of developing serious forms of the disease but which play an important role in transmission, reduces the circulation of the virus and therefore indirectly protects the most vulnerable,” writes the study’s authors.

“If it is confirmed that the vaccines have a real impact on susceptibility to infection, we may consider extending the vaccination to younger people earlier,” Crépey said. It would do a faster job of reaching the 90% population target.

But even if this threshold is not reached in the autumn, “we will still benefit from the vaccination campaign, as each person vaccinated reduces the rate at which the virus spreads,” Dhersin explained. According to mathematics, the authorities should slowly but surely remove or adapt the Covid-19 restrictions.

“One can imagine a reopening of cultural sites where the public would have to wear a mask, for example,” Dhersin offered.

For residents of France, it can only be a matter of redefining the concept of “normal life”.

This article has been translated from the original into French.