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Did you know that the vaccination principle has already existed for several centuries? And that Pasteur isn’t the first scientist to have experienced it? So how do vaccines work, anyway? We will explain everything to you.
While announcements have been circulating in the last few days the effectiveness of several vaccines against Covid-19, let’s go back to the ancient history of vaccination, how it works and what is at stake.
From smallpox to anger, from Jenner to Pasteur
In the 18th century, the smallpox (also called “smallpox”) it is wreaking havoc in Europe. However, scientists note that farmers who contract vaccine – a relatively benign form of cowpox for humans – appears to be protected. In 1796, doctor Edward Jenner then attempted to inoculate a child with pus taken from a person infected with the disease: the guinea pig would finally resist smallpox. The scientist arrives, for the first time, to experience a semblance of “vaccination”.
A smallpox vaccine thus became mandatory for British children in 1853, then in 1902 in France. But it comes just before a more famous discovery, that of the rabies vaccine by Louis Pasteur. The first injection given to a child, bitten by a dog suspected of being rabid, was successful in 1885. This vaccine, however, was different from that against smallpox: it was developed by a attenuated viral strain. A few years will be enough to see the appearance of the one against tuberculosis, diphtheria, tetanus and pertussis.
Having killed around 300 million people during the 20th century, the smallpox is declared eradicated by the World Health Organization (WHO) on May 8, 1980 through vaccination. But if the vaccine is sometimes considered as the best medicine in the world, is also the source of distrust. So much so that according to a poll Odoxa-Dentsu consultation for franceinfo is Le Figaro published on November 12, 2020, 50% of French respondents (1,005 people) would refuse to be vaccinated against Covid-19 if a vaccine were soon distributed in France.
But how does a vaccine work?
To understand vaccination, let’s first take a look at the mechanisms of immunity. When our body is first confronted with a pathogen, it asks some of its cells to produce antibody, proteins that will fight against this particular bacterium or virus. It turns out that the immune system has very good memory : when our body is confronted with this pathogen again, these fighting cells are reactivated eliminate the intruder as quickly as possible and not suffer from the pathology for which he is responsible.
It is on this same principle that vaccination is based. Made with small amounts of bacteria or viruses (weakened or dead, so that they lose their dangerousness) and injected into the body, vaccines activate the production of “memory” cells. The body develops a “supply” of antibodies without causing disease. It will thus be best prepared in contact with pathogens. This is ultimately what it is calleddisease immunityand the goal of all vaccines. The duration of their protection varies. Here because reminder sometimes they are needed to reactivate it.
What about collective immunity in all of this?
Collective immunity corresponds to aa percentage of people, in a population, possess antibodies to an infectious agent. Once this level is reached, by exposing individuals or protecting them with a vaccine, the virus or bacterium no longer circulates and the epidemic stops. This threshold depends on each pathology. Against the measles, is obtained when about 95% of a population is immune. The rest (remaining 5%) are protected, as the disease no longer spreads. The papilloma virus it is also a good example (watch the video at the beginning of the article).
However, in the case of Covid-19, immunology is still poorly understood. Coronavirus re-infections or the situation in the city of Manaus in Brazil concern: if it is possible to be affected by the virus several times – and especially, without inoculation and its available reminders – collective immunity, just like individual immunity for that matter, seems understood. This explains why the announcements of the development of effective vaccines by Pfizer, Sanofi or Modern have long been awaited.
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