Can we still hope to achieve collective immunity with the Delta variant? – The world

Should we draw a line on collective immunity, this horizon presented for several months by epidemiologists as an objective that would bring us closer to the end of the epidemic?

While most countries have since the beginning of the year embarked on a vaccination race in the hope of achieving protection for their population allowing the relaxation of measures restricting freedoms or barrier gestures, a sentence from beyond -Manche caused confusion. “With this variant [Delta], we are in a situation where collective immunity is not possible to achieve, because it always infects vaccinated individuals ”, explained, on August 10, to British parliamentarians Andrew Pollard, director of the Oxford Vaccine Group, which developed the AstraZeneca vaccine with the Anglo-Swedish pharmaceutical group.

A more transmissible variant, vaccines that do not completely block infections and the transmission of the virus … The summer climate has also caused people to say, in the Sunday newspaper August 15, to Alain Fischer, President of the French Vaccine Strategy Orientation Council (COSV), that “The view that we can have of group immunity today is unfortunately not that of eighteen or even six months ago”. He specifies at World : “We are a little too attached to collective immunity”, recognizing that “It is perhaps a bit our fault because it has been put forward a lot by epidemiologists and immunologists”.

However, this central notion remains relevant as long as we agree on its definition. More importantly, the questions about the possibility of achieving or not this collective immunity do not call into question the need to vaccinate the largest possible proportion of the population.

• Is collective immunity achievable?

Collective immunity (group, herd or gregarious) refers to a phenomenon allowing the protection of non-immunized people when a certain proportion of the population is protected either by natural infection or by vaccination – both of which lead to a response. immune system and antibody production.

In the event of an epidemic, it will therefore be a question of aiming for a level “From which an infected subject (…) will transmit the pathogen to less than one person on average, bringing the epidemic to extinction, because the pathogen encounters too many protected subjects ”, according to the definition of the Institut Pasteur.

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