The Omicron variant, which spreads at a rapid pace, undermines the effectiveness of vaccines.
In any case, this is the observation that emerges from several studies carried out in particular in South Africa and the United Kingdom.
At the end of last week, the British health agency (UK Health Security Agency) thus indicated in an analysis - which is intended to be cautious - that the effectiveness of the third dose (or booster) declines nearly ten weeks after the injection .
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In detail, the British study suggests that a three-dose vaccination schedule performed only with Pfizer-BioNTech doses confers 70% protection against symptomatic forms of the coronavirus linked to the Omicron variant.
But this immunity wanes quickly thereafter.
Thus, this protection is only 45% after ten weeks, according to the data of the study.
The situation is different for patients who have received doses from other laboratories, or a "
mixture
".
For patients who had an AstraZeneca vaccine first, then a Moderna or Pfizer-BioNTech booster, the protection after ten weeks would be 45% and 35%, respectively.
Evolution of vaccine efficacy with a scheme composed of two doses of AstraZeneca vaccine, and alternatively of a Pfzer-BioNTech or Moderna booster.
UK Health Security Agency
Evolution of vaccine efficacy with a schedule consisting of two doses of Moderna vaccine UK Health Security Agency
Last case: patients who first received two doses of Pfizer-BioNTech vaccine before getting a booster with a dose from the Moderna laboratory.
In France, this scheme only concerns people over the age of thirty.
They seem to be the most durably protected, since the effectiveness of the vaccine would be maintained between 70 and 75% after ten weeks.
Evolution of vaccine efficacy with a scheme composed of two doses of Pfizer-BioNtech vaccine, and alternatively of a Pfzer-BioNTech or Moderna booster.
UK Health Security Agency
Protection against severe forms
The results of this study should be examined with caution, as underlined by the British health agency, which warns against possible biases linked to the profile of people infected with Omicron.
In addition, the sample examined in this study is relatively small, since it is composed of 147,587 cases of the Delta variant and 68,489 cases of the Omicron variant.
Despite everything, these results add to a set of studies published in recent weeks which raise the question of the efficacy of the vaccine against this variant.
So, according to an analysis of real-life data released on Tuesday, December 14 by a South African health insurance group, protection against contamination from the new variant would drop over time to reach 30% under a diagram produced with two doses (only) of Pfizer-BioNTech vaccine.
On the other hand, this study finds an effectiveness against the serious forms (70%).
It is supported by the analysis published by the British health security agency, which estimates that people infected with Omicron are between 50 and 70% less likely to be hospitalized.
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But here again, the results must be examined with caution, since, as the agency points out, the analysis remains "
highly uncertain because of the low number of patients affected by Omicron currently in hospital, the impossibility of effectively measuring all of them. previous infections and limited spread of Omicron among older groups
”.
