Covid-19: everything about the infectious challenge to speed up the arrival of a vaccine

Since the emergence of the new Sars-CoV-2 coronavirus, the vaccine race has been on. But normally, if all stages of development are scrupulously followed, creating a new vaccine will take time, one to two years at the very least, and in the best of cases.

Also, to accelerate the development of the vaccine against the coronavirus, the term infectious challenge has resurfaced. Used until the 1970s, this technique consists of evaluating the efficacy of the vaccine candidate by injecting the virus into healthy volunteers, or knowingly infecting them in some other way. Just before infection, the volunteers are divided 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.

From the beginning of April, several teams of scientists around the world raised the possibility of using the infectious challenge again in order to go faster in the evaluation of vaccine candidates currently in the testing phase.

Only here, as the Scientific Council underlines, unfavorable to the use of this challenge, this techniqueraises ethical questions. After all, isn’t the fundamental principle of medicine to cure and “do no harm”, As the Latin phrase says so well“Primum non nocere“Of the Hippocratic Oath, taught to medical students?

While this approach may be useful for the evaluation of other vaccines in the absence of immune correlates of protection, its relevance in the case of SARS-CoV-2 seems questionable for both scientific and ethical reasons.”, Thus indicates the Scientific Council in his last opinion. At the scientific level, “the existence of animal models of SARS-CoV2 infection, even imperfect, does not require the evaluation of protection in young healthy volunteers, the results of which would not be more transposable than those of animal models, to vulnerable people, main targets of protection”, Estimates the Scientific Council.

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

As for the ethical level, the Scientific Council considers that “even if the level of risk 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”.

The fact remains that if the French scientific authorities are opposed to it, other countries are less reluctant to resort to the infectious challenge. The platform 1DaySooner thus counts more than 32,600 volunteers from 140 countries.

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