“We can discuss anything except numbers.” On Twitter, biochemist Eric Chabrière, close collaborator of Professor Didier Raoult, assured, Saturday January 15, that “the vaccinated [avaient] more risk of catching Covid than non-vaccinated people”. His comment, widely relayed on the social network, is accompanied by a graph which represents the proportion of positive cases according to the vaccination status. data, “official”, come from the Department of Research, Studies, Evaluation and Statistics (DREES), supports Eric Chabrière. But is this graph authentic and is his reading of it true or “fake”?
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These curves come from the CovidTracker epidemic monitoring site and were indeed produced using data from DREES, available in open source. The graphic makes it possible to observe the proportion of positive cases for Covid-19 recorded each day, all age groups combined, according to the vaccination status.
Thus, on January 2, there was the equivalent of 17,008 positive cases for 10 million unvaccinated. At a comparable population size, 22,255 positive cases were then identified among the “vaccinated”, that is to say people who received a complete initial vaccination scheme, but without a booster dose. These are the two indicators to which Eric Chabrière refers.
“The graph is true: there were, at the beginning of January, in proportion, a little more positive cases among the vaccinated (complete diagram) than the non-vaccinated”, reacted Sunday on Twitter Guillaume Rozier, the founder of CovidTracker. However, the computer engineer adds that these curves do not make it possible to conclude that the virus circulates more among vaccinated than among non-vaccinated.
Indeed, the data has at least one major bias: this graph includes a series of data concerning children and adolescents aged 0 to 19 years. An age group that includes “specificities”, “especially with regard to his very partial vaccination”, warns the DREES in its report published on January 14 (PDF link). For its part, the CovidTracker site makes it possible to visualize the number of new daily cases among 0 to 19 year olds, according to the vaccination status, but specifies that the curves are not “interpretable”, Due to “vaccination data too low”.
And for good reason, the category of 0-19 year olds (which represent 23.7% of the total population according to INSEE data) actually includes four different populations from the point of view of the vaccination campaign: children from 0 to 4 years old, not eligible for vaccination, children from 5 to 11 years old who have only had access to vaccination since December, adolescents from 12 to 17 year olds whose vaccination was generalized in June, and finally those over 18-20 years old, eligible since May. Thus, on January 16, only 2% of children aged 5 to 11 had received a complete initial vaccination schedule, compared to 79.4% of 12-17 year olds.
Contacted by franceinfo, the DREES explains that “Looking at the numbers of tests, with a comparable population size by vaccination status, aggregated over these ages, amounts to comparing the incidence for very young unvaccinated children with that of adolescents who are mainly vaccinated”. In other words, this statistical category of 0-19 years mixes a population of widely vaccinated adolescents with children who have rarely had recourse to it.
Moreover, the children were also “little tested” early January, advances Guillaume Rozier on Twitter. According to data from Public Health France, ebetween December 27 and January 2, we were counting 5,569 tests per 100,000 people under the age of 10, compared to 12,126 tests per 100,000 in the rest of the population. Among the youngest, there were “much fewer cases than in other age groups”, says the computer engineer. This phenomenon therefore contributes to distorting the number of positive cases among the non-vaccinated within the population as a whole.
The data on 0-19 year olds being included in the graph shared by Eric Chabrière, it is impossible, according to the DREES, to deduce that on the scale of the whole population, the vaccinated are proportionally more infected. by Covid-19 than the unvaccinated.
“The conclusion obtained is therefore erroneous in our opinion and it is advisable to favor charts over 20 years and more for these analyses.”
The Research, Studies, Evaluation and Statistics Departmentat franceinfo
By removing the category of 0-19 year olds, it is clear that at a comparable population size, the number of new positive cases among those vaccinated without a booster dose (22,997 cases for 10 millione vaccinated aged 20 and over) is lower than that observed in the non-vaccinated (29,674 cases for 10 million non-vaccinated people aged 20 and over).
Let’s look at the number of positive cases by removing those under 20. There are, proportionally, more positive cases in the unvaccinated than in the vaccinated. And this rate is even lower in those vaccinated with booster (three times lower). pic.twitter.com/f3bEB6o6ig
— GRZ (@GuillaumeRozier) January 16, 2022
Among those aged 20 and over, the number of positive tests is proportionally “much higher for unvaccinated people than those with full status without a booster”, concludes for its part the DREES, in its report.
She adds that “unvaccinated people are clearly over-represented, compared to their share in the general population, among those tested positive by PCR for Covid-19″. Between December 6, 2021 and January 2, 2022, when they represent 9% of the population aged 20 and over, they then comprised 19% of people who tested positive and reported symptoms.
Furthermore, Eric Chabrière’s commentary does not take into account vaccinated persons who received a booster injection, and “who are even less frequently tested positive”, underlines the Drees. As of January 2, the rate of positive cases among vaccinees with booster (9,672 cases for 10 millione vaccinated with booster, aged 20 and over) was youthree times lower than that of the non-vaccinated.
The data on vaccinees with booster appear all the more relevant as the rate of neutralizing antibodies, which block the virus, generated by an initial two-dose vaccination, tends to drop gradually over the months. “We now know that, without a booster dose, immunity declines over time, and declines all the more as we get older”, supports with franceinfo Sandrine Sarrazin, Inserm research fellow at the Marseille-Luminy immunology center.
The context of active circulation of the Omicron variant, now the majority in France, also encourages taking into account data on vaccinees with booster. Faced with this variation, “uno booster dose is needed to restore [les niveaux] of neutralizing antibodies and reduce the risks of infection, hospitalization, hospitalization and severe form”, noted Public Health France in its analysis of variants published on January 5.]
If vaccine protection against symptomatic infections related to Omicron “is much weaker” than against the Delta variant, “the recall always makes it possible to significantly reduce the risk”, confirms the DREES in its note.