Herd immunity, also known as herd immunity, refers to “the indirect protection against an infectious disease that is obtained when a population is immunized by vaccination or from a previous infection”specifies the WHO.
The latter argues “the pursuit of herd immunity through vaccination and not allowing a disease to spread within a part of the population, as this would lead to unnecessary cases and deaths.”
Letting go of sickness or 0 case policy?
Let the disease “spin” to achieve collective immunity and get out of the crisis more quickly, this is the strategy that Sweden has chosen especially when the virus has arrived on its territory by not imposing, for example, containment measures or wearing a mask.
The Swedish government then backed down a few months later, faced with a significantly higher death toll than in other Nordic countries which had enacted much more restrictive measures.
On the other side of the world, where the virus originated, the opposite option was preferred. China chose to implement an ultra-strictive zero Covid policy in early 2020, before abruptly lifting it nearly three years later in the face of exasperation from its population and the impact on its economy.
Predictable result: within a population without collective immunity because little or no exposure to the virus and its variants and weakly vaccinated, contamination explodes. Some experts believe we could pass the one million death mark in the spring.
An epidemic still active
And in France? From March 2020 to today we have experienced confinements, social distancing, barrier gestures, curfews, screening, isolation, then, when possible, vaccination.
According to the latest data from Public Health France, as of January 5, 79% of French people had received a complete primary vaccination (the 2 doses) and 60% a complete primary vaccination and at least one booster dose.
As for the actual reproduction rate of the virus (the number of non-immune people an infected person can infect), it has recently dropped below the fateful bar of 1, to settle at 0.6. In other words: the epidemic is in decline. But it is not extinct for all this.
How to explain it, when if we take into account the successive waves of contamination and vaccination, herd immunity reached more than 90% of the population last March, according to the Academy of Medicine?
An unstable virus
Because, unlike the measles or smallpox virus, which you only need to encounter once to be immunized for life, this virus is very unstable: half a dozen variants have followed from the original virus, including the formidable Omicron. Increasingly contagious variants, with greater potential for reinfection: reinfections after initial contamination and infections after vaccination are not uncommon.
This is the other characteristic of the latest Omicron variants: they show a great ability to evade vaccination and infection-induced antibodies, according to a study published in The New England journal of medicine in June. Or before the commercialization of bivalent vaccines, in particular directed against the BA.4 and BA.5 variants.
Will these vaccines, authorized in France in November, finally achieve this famous collective immunity? Again, difficult to predict: on January 2, only 16.30% of 60-79 year olds and 19.60% of 80 year olds and over had received a reminder adapted to Omicron’s subvariants. Another parameter to take into consideration: asymptomatic patients, by nature difficult to quantify.
In any case, the health authorities remind us, even imperfect vaccines remain the best weapon to reduce the transmission of viruses and limit the risks of serious forms.
