Halting the spread of an infectious disease in a population by immunizing a certain percentage of individuals. The principle of group immunity, also known as collective, herd or herd immunity, which the British government is banking on to combat the Covid-19 epidemic, is well known with vaccinations. In addition to protecting individuals, vaccines help protect other people. Often, vaccination prevents the multiplication of the pathogen, virus or bacteria, in the vaccinated person. She is therefore no longer likely to transmit the infection to her loved ones, and she acts "Vis-à-vis the rest of the population, as a barrier against the pathogen by interrupting the chain of transmission ", According to an educational file from Public Health France.
Can this strategy be applied knowingly to the new coronavirus, against which there is no vaccine and to which a priori 100% of the population is sensitive? While all countries advocate measures of social distancing and confinement, the English are the only ones to bet on collective immunity, estimating that if 60% of the population is infected, this would avoid a second epidemic peak in 2021. A policy challenged on all sides, because it was considered risky. Even the British Roy Anderson, one of the great specialists in group immunity and who theorized this notion, does not seem to envisage it in the present case. In an article published online March 9 in the journal The Lancet, on the contrary, he insisted on measures of social distancing and early isolation of the sick.
In addition, projections of the impact of SARS-CoV-2 on laissez-faire are very pessimistic. The Neil Ferguson team (Imperial College, London) worked on this option. In the case of France, if no mitigation or containment action was taken, its models predicted between 300,000 and 500,000 deaths in the most pessimistic hypothesis, the resuscitation services being quickly submerged. These figures, presented to the French executive by the council of experts set up by the government, have contributed to the hardening of the measures of "social distancing" taken in recent days. Neil Ferguson is expected to present projections for different European countries in the coming days.
