The idea of letting the covid-19 virus circulate freely to achieve herd immunity, shuffled at the beginning of the pandemic, is increasingly emerging as a dangerous mirage, according to many scientists.
It is about allowing a certain proportion of the population to become infected with the virus so that the pandemic stops on its own, in the absence of new people to infect.
But after months of health emergencies, “we are very, very far” from reaching that threshold, Frédéric Altare, an immunity specialist at the French National Institute of Health and Medical Research, told AFP.
The World Health Organization (WHO) made it clear this week: “Never, in the history of public health, has herd immunity been used as a strategy to respond to an epidemic, let alone a pandemic. It has been problematic since scientific and ethical point of view, “said its CEO, Tedros Adhanom Ghebreyesus.
“Letting go of a dangerous virus, from which many things escape us, is simply unethical. It is not an option,” he insisted.
The WHO estimates that in most countries, 10% of the population could have been infected with SARS-CoV-2.
– Trump statements in favor –
Billions of people can therefore still be infected with this virus, more lethal and contagious than the flu and for which there is no vaccine.
In May, the WHO already warned that countries in favor of pursuing herd immunity were facing “a very dangerous calculation.”
Yet President Donald Trump has often championed this idea.
This month, a group of scientists launched an appeal, “The Great Barrington Declaration”, in favor of letting the virus circulate among young people in good health – and therefore susceptible to not becoming seriously ill -, in order to protect the young. most vulnerable.
An appeal supported by the White House, according to the US press.
The main benefit of this strategy would be to avoid the economic, social and health damages caused by the pandemic, by not having to decree, for example, new generalized confinements.
It’s “a mistake,” 80 scientists responded in an open letter published in the medical journal The Lancet on Thursday. “An uncontrolled transmission among the youngest would be very risky in terms of health and mortality for the population as a whole,” they affirm, citing the risk of saturation of health systems as an example.
– The minimum threshold –
Sweden, which chose not to confine its population or close schools, bars and restaurants during the first wave, has a mortality rate that places it in the top 15 places in the world, with respect to the size of its population, according to data from Johns University Hopkins.
In addition, it is unknown how long immunity lasts and cases, although rare, of reinfection are known. “It is possible that the antibodies are reduced with time,” recalled a WHO official, Maria Van Kerkhove, last week.
“Reinfections show that we cannot rely on immunity acquired through natural infection to achieve group immunity,” wrote Dr. Akiko Iwasaki, an immunity specialist at Yale University.
Some advocates of natural herd immunity also argue that their threshold, generally estimated for a virus between 60 and 70% of the population, would actually be lower, because not everyone gets COVID-19.
Recently, it was discovered that some people are already protected against SARS-CoV-2 when they become infected, despite not having previously been in contact with it, according to Frédéric Altare.
Instead of antibodies, these people develop a cellular immunity, thanks to a certain type of white blood cells. Having “known” other infectious agents similar to SARS-CoV-2, these globules identify the latter as a danger and attack it.
“This means that the figures that show that between 5 and 10% of the population could already be immunized are surely underestimated, but we do not know to what extent”, continues Altare.
But even taking into account all the relevant factors, the minimum percentage necessary to achieve herd immunity “would be 50%” and therefore a considerable number of deaths would occur along the way, he adds.
Thus, herd immunity must go through “safe and effective vaccines,” according to Dr. Iwasaki.