What can we conclude from the first study on the impact of vaccination in a real situation in France?



This is a study that was particularly eagerly awaited. While many countries had already referenced the impact of vaccination in a real situation, France had never produced such statistics at the national level, until Thursday evening.
A study of the Drees (Department of Research, Studies, Evaluation and Statistics) is finally providing data on the vaccination status of positive coronavirus cases in France between June 28 and July 4.

20 minutes takes stock of these results and what can be concluded from them.

What does the study say?

6% of cases testing positive for coronavirus between June 28 and July 4 are fully vaccinated people (i.e. two weeks after the second dose, or a single dose in case of previous coronavirus infection or Jansen vaccine). At the time, 32% of French people were considered to be fully vaccinated.

11% of positive cases had received their first dose for more than 14 days or their second dose for less than 7 days, 3% had recently received their first injection. This leaves 80% of cases without any vaccine dose.

This “resistance” of vaccination works in all age groups, states the Drees. In other words, whatever the age group, the percentage of vaccinated among people who test positive is lower than the percentage of unvaccinated people.

The vaccine rate drops further if we focus on symptomatic people. There are then only 4% of people fully vaccinated, 9% with a first dose received for more than fourteen days or their second dose for less than 7 days, 4% recently injected, and 83% of the symptomatic n ‘ had received no dose.

What to conclude from this study?

For the doctor and public health researcher Mickael Ehrminger, “This is already a first positive signal, which shows that if the vaccine protects in the first place against serious forms and death, it also seems to reduce contamination. “

“This study shows that, in a population where complete vaccination is not yet the majority, people who are not protected will be much more exposed than the vaccinated, it confirms that”, notes Eric Billy, researcher in immuno-oncology

But how is it that more people test positive two weeks after their first dose than just a few days after? One of the explanatory factors could be what is called “vaccinee syndrome”, that is to say a relaxation from the first shot of the vaccine while it is necessary to wait two weeks after the second dose for be considered to be genuinely protected. “Suddenly, we see a lot of infections in the field after the first dose because of this release. That may explain this percentage, ”supposes Mickael Ehrminger. He adds: “This study shows in any case the importance of the two doses, not always well communicated in France. It is important to see that the complete vaccination brings an improvement over the partial vaccination. “

What are the possible biases of this study?

Two major biases can be deplored. First, vaccinated people get less tested than unvaccinated people. In fact, it is possible that the percentage of positives is underestimated because of this.

Second, the study focuses on cases between June 28 and July 4, a period when we know, the majority of positive cases concern young people mainly between 10-19 years and 20-29 years. It is in these two age groups that the incidence has mainly increased. “And this is not so much due to their lack of vaccination as to the fact that they mostly go to bars and restaurants, that they have many social contacts,” recalls Mickael Ehrminger. However, these age groups are by far the least vaccinated, the fault of an open vaccination very late (May 31 for adults under 50 without comorbidities, June 15 for 12-17 years). This can potentially boost the number of positive unvaccinated cases.

And now ?

If this is a first study, finally, on the real impact of the vaccine in France, remains that it misses the main subjects: hospitalizations, resuscitations and deaths. “Studies will come later, it is already a first step”, reassures the doctor.

For Eric Billy, “it is important to release its figures on vaccine efficacy in hospitalization and death, because the discourse against the vaccine lasts a lot on positive cases. However, the vaccine is used above all against severe forms, ”he recalls. For example, in the UK, the outbreak of cases is decorrelated with hospitalizations, much less than in previous waves of positive cases.

In addition to this, you will need to know more about it.

Even if he warns that with the production of figures – percentages or raw data – remains the necessary context, to properly interpret these data and not to make the bed of anti-vaccine discourse. It’s all well and good to have data, but you still have to understand it.



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