The achievement of herd immunity for Covid-19 is a "false promise" that risks bringing new grief and untold suffering: the title chosen by the Nature site for an article in which the contrary voices of epidemiologists and experts are collected is explicit of public health which explain point by point the weaknesses of this theory.
"Surrendering the virus" is not a sustainable strategy according to Kristian Andersen, immunologist at the Scripps Research Institute in La Jolla (California), one of the experts interviewed by Nature.
"It will bring unacceptable and unnecessary death and suffering. There is no magic wand that we can use. We have to face reality: before now we have never achieved herd immunity through natural infection with a new virus and SarsCoV2. unfortunately it is no exception ".
Usually we speak of 'herd immunity' (or better still 'herd protection') in reference to vaccines which, administered to a high percentage of the population, allow to indirectly defend even those people who cannot get vaccinated or who do not respond adequately to the vaccine.
"I am confused that the term herd immunity is now being used to define how many people have to be infected before this is over," emphasizes Marcel Salathé, epidemiologist at the Federal Polytechnic School of Lausanne.
Experts underline how complicated it is to calculate and monitor the achievement of the threshold of infections that would allow herd immunity, both because it is necessary to take into account the human behaviors that vary the transmission rate of the virus, and because the real immunity data they are observable only after a long time.
Although the calculations may indicate a precise number, there is not an exact moment when herd immunity is triggered, but a gradual and variable transition.
Even once reached, this condition would not a priori exclude the outbreak of outbreaks, as has already occurred for other diseases in areas where vaccinations are falling.
Finally, the duration of immunity remains to be assessed: if it were to persist for a year, herd immunity would never be achieved without a vaccine, according to epidemiologist Caitlin Rivers of the Johns Hopkins Center for Health Security in Baltimore.