July 2, 2022

Covid-19: why are there now more vaccinated than unvaccinated admitted to hospital?

In their eyes, this demonstrates the supposed ineffectiveness of vaccines against Covid-19. The “antivax” sphere has seized in recent days data on hospitalizations according to vaccination status, very interesting to examine but which can be misinterpreted. They are published every week by the Directorate of Research, Studies, Evaluation and Statistics (DREES).

This time around, they would show that the majority of patients diagnosed with Covid-19 and hospitalized are vaccinated. But things are far from that simple. We explain to you.

What you may have read or heard

“There are now more people vaccinated in hospital for Covid than unvaccinated”, an internet user got carried away, who defines himself as a “conspirator today” and “whistleblower tomorrow”.

Why is this misleading

On paper, taken in isolation, these statements are almost correct. The latest data available goes through October 30. Over the last five days, among all the patients admitted daily to the hospital for Covid-19, there are indeed more vaccinated than unvaccinated (respectively 105 against 93 on October 30). These are therefore daily admissions to the hospital, and not patients hospitalized at time T. The two curves are close to intersecting for admissions to critical care, as well as for the deaths recorded each day at the time. ‘hospital.

But such an analysis is misleading, as Le Parisien has repeatedly explained. Because it should not be based on absolute values. The more the vaccination coverage of a population increases, the more the proportion of vaccinated patients among those hospitalized is likely to increase. Take the extreme (and purely theoretical) example of a 100% vaccinated population. As vaccines do not protect 100% against severe forms (but rather 90% or even 95% during the first months), some people would get sick and would be hospitalized. And in the end, 100% of patients admitted to hospital would be… vaccinated.

This is why the argument of saying “8 out of 10 hospitalized patients are not vaccinated”, regularly repeated by the government in its advertising campaigns this summer, was going to backfire. “That 80% figure doesn’t make a lot of sense. In a few weeks, with – fortunately – the vaccination coverage improving, the percentage of vaccinated patients among those hospitalized is expected to increase. This will absolutely not mean that vaccines are less effective, ”warned epidemiologist Mahmoud Zureik at the end of August.

With good reading

To properly interpret these data, they must be related to the population of each group. Also on October 31, there are 56 daily hospitalizations for 10 million unvaccinated and “only” 21 for 10 million inhabitants (all ages) immunized.

But these data are biased because children and adolescents represent a very large part of the unvaccinated population, but a very low number of hospitalizations. It is better to look at age group by age group. Among 40-59 year olds, there are 137 daily hospitalizations for 10 million unvaccinated and 7 among vaccinated. For those “80 and over”, these values ​​are 374 and 116.

A decrease in the effectiveness of vaccines?

In addition to the very high vaccination coverage (nearly 90% of adult inhabitants are vaccinated in France), another element could explain why there are now more vaccinated than unvaccinated among the patients admitted every day to the hospital: the drop in effectiveness of vaccines over time. Several studies attest to the protection against infection, and some work also suggests an impact for severe forms.

With the data from the DREES, we can calculate the ratio between the rate of hospitalization among vaccinated and unvaccinated. It turns out that it has declined over the past few weeks. All ages combined, for an equal population, there were 5 times more unvaccinated than vaccinated admitted each day to the hospital this summer, against less than 3 now. If we focus on the population aged 20 and over, the ratio has dropped from 12 to 7 in a month and a half.

It is in the oldest bracket (80 years and over) that the drop seems most marked (from 10 in June to 3 now). This could confirm that vaccines are less and less effective, especially in our elders. But beware: these data do not make it possible to precisely establish the protection they confer. Several external factors, starting with the restrictive measures, come into play and are not taken into account. All of this reminds us that “vaccination alone is not enough” to contain the epidemic, as epidemiologists insist.

In summary :

  • At the end of October, the number of vaccinated patients exceeded that of unvaccinated patients among all those admitted daily to hospital for Covid-19.
  • This observation was expected, in particular because of the increase in vaccination coverage. For an equal population, there are always significantly more hospitalizations among the unvaccinated than among the vaccinated.
  • Data from the DREES seem to attest to a decline in the effectiveness of vaccines against severe forms, especially in the elderly.