On Monday, the Haute Autorité de Santé (HAS) recommended a “reactive” vaccination strategy against the most dangerous variants of the coronavirus, such as the delta variant, which is estimated to be 60% more contagious than the alpha variant itself. Up to 50 to 74% more transmissible than the original strain of Covid-19.
Reactive vaccination consists of inoculating ‘very rapidly’ each footnote of each positive case of a variant of concern once the latter has been identified. By footnote, HAS refers to “all individuals at home in the detected condition, persons at their workplace and/or at school/university”.
Reply, isn’t it too late already?
The strategy can leave you skeptical on the first impression. What is the point of vaccinating relatives when a person is already positive, and the vaccine requires two doses (except Jansen) with an interval of several weeks followed by another two weeks to offer maximum immunity? In fact, although the first dose is not ideal, the first dose provides the onset of immune protection after twelve days. Very partial protection, far from enough for you to stop applying barrier measures after the first dose, but – in this case – it’s always better than nothing. Thus, if a double dose of the mRNA vaccine (Pfizer-BioNtech/Moderna) protects 90% of the risks of hospitalization, the first dose still protects at 30%, and also reduces the risk of catching the delta variant by 30%. If the first dose is not enough (we allow ourselves to insist), then it will not be useless for all that.
Very good, but if this first dose is effective only after twelve days, what is the use for those who turn positive? As a reminder, an individual is generally contagious within five to fifteen days after becoming infected. And again, this means that he will test positive once he has the virus. In the most likely hypothesis that he was tested after developing symptoms, the peak of infection has already passed (generally occurring two days before the first symptoms appear, and the individual is no longer contagious between seven and ten days after onset). Suffice it to say that if an infected person contracted the virus, he would have transmitted it before the effect of the initial vaccination occurred in his relatives.
break transport chains
Particularly due to the incubation times of the coronavirus, HAS does not recommend a loop strategy, which consists of vaccinating contact cases and their contact cases. Due to the incubation period of the virus (about five days) compared to the time of onset of protection from the vaccine (about twelve days after the first dose), the time for initiation of protection is already too late for contacts from already contaminated contacts.
No win then? Well, yes, because we must not forget about pollution from recoil. “The strategy aims above all else to avoid a second generation of contamination cases because in fact we will probably not be able to prevent people from among those ‘contacts’ who are already infected from becoming infected,” notes Marie-Paul Kenney, a virologist, vaccinologist and French public health expert. .
Let’s take an example. Martin, Laurie, Stephanie, and Julian work for the same company. Martin tested positive for the delta variant after the first symptoms appeared. As a result, Laurie, Stephanie and Julian were vaccinated. AJ + 12, so they have the onset of immunity. Unfortunately, it was too late for Laurie, who didn’t know it but was injured by Martin the day before the test. Too late, too, for Stephanie, who is polluted by Laurie in turn. For this chain of transmission there, in fact, vaccination was not necessary. But now, at D+13, Stéphanie, who still doesn’t know she’s positive, is taking a coffee break with Julien. Whereas without the first injection, Julian would have contracted the infection in turn, and the first dose protected him enough to avoid infection. Thanks to the reactive strategy, Stephanie’s chain of contamination stops, while without everyone’s basic vaccination, Julian would have become infected and could in turn infect other people. These are the bounces that the reaction strategy intends to avoid.
In search of lost time
Effective strategy? Opinions differ. For Marie Paul Kenny, “From the moment we stepped in too quickly, it’s a very effective strategy. It cuts the chains of person-to-person transmission.” Eric Bailey, a researcher in immuno-oncology, is even more skeptical: “We must not lose sight of the fact that vaccination is above all prevention rather than cure. Once a mass is detected, it is often too late for those around it. Basic vaccination, even after twelve days, provides Only very partial protection. Vaccination is not a ‘reaction,’ it is an expectation.”
For the researcher, we must push first and foremost toward more initial vaccination even before a positive case is detected. Eric Bailey points out that “people should be vaccinated, and health authorities should think about how to combat the decline in primary vaccines.” The same message for doctor and vaccinator Christian Lehmann: “We have made people think that vaccination can wait until holidays or even back to school, but now is the time to get vaccinated as much as possible. Variable delta is already present throughout the territory. So we must vaccinate and vaccinate and vaccinate. “The time has come for highly active vaccination, rather than reactive vaccination.
