What is the infectious challenge, planned to accelerate the arrival of the anti-Covid vaccine?

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To accelerate the development of the Sars-CoV-2 vaccine, the term "infectious challenge" is mentioned. We tell you what it means and why the Scientific Council is against it.

Infectious challenge: what does this technique consist of?

To accelerate the development of the coronavirus vaccine, the term "infectious challenge" has re-emerged. Used until the 1970s, this technique involves evaluating the efficacy of the vaccine candidate by injecting the virus into healthy volunteers or knowingly infecting otherwise.

Just before infection, the volunteers fall into two groups: some receive the vaccine, while others receive a placebo. Several months later, both groups are tested to measure their immune response to the infection. If the vaccine is effective, the group that received it will have had a better immune response than the group that received a placebo.

Starting in early April, several teams of scientists from around the world raised the possibility of reusing the infectious challenge to speed up the assessment of vaccine candidates currently in the testing phase.

Ethical and scientific obstacles.

However, as the Scientific Council emphasizes, unfavorable to resort to this challenge, this technique raises ethical questions. After all, is not the fundamental principle of medicine to cure and "do no harm", as the Latin phrase "Primum non nocere" of the Hippocratic oath, taught to medical students, aptly says?

"If this approach can be useful for the evaluation of other vaccines in the absence of protective immune correlates, its relevance in the case of SARS-CoV-2 seems questionable for scientific and ethical reasons", as stated by the Scientific Council in its last opinion.

At a scientific level, "the existence of animal models of SARS-CoV2 infection, even imperfect, does not require recourse to the evaluation of protection in healthy young volunteers, whose results would not be better, than those of animal models, to vulnerable people, the main protection objectives, "estimates the Scientific Council.

Clearly, although imperfect, the animal models that exist to test the effectiveness of a vaccine appear to be sufficient. Especially since testing the vaccine in young and healthy people would not allow a good representativeness of the population, since Covid-19 is mainly a danger for the elderly or people with chronic pathologies.

Regarding the ethical level, the Scientific Council considers that "even if the risk level is low, we cannot rule out the possibility of an accident occurring in these volunteers, in the absence of proven curative therapies for Covid-19".

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