The real story of vaccination

Did you know that the principle of vaccination has already existed for several centuries? And that Pasteur is not the first scientist to have experienced it? So how do vaccines work, anyway? We will explain everything to you.

While in recent days, announcements have been flowing about 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 pox to rabies, from Jenner to Pasteur

In the 18th century, the smallpox (also called “smallpox”) is wreaking havoc in Europe. However, scientists note that farmers who contract vaccine – a relatively benign form of cowpox for humans – seem to be protected. In 1796, the doctor Edward Jenner then tried to inoculate a child with pus taken from a person infected with the pathology: the guinea pig would finally resist smallpox. The scientist comes, for the first time, to experience a semblance of “vaccination”.

A vaccine against smallpox thus became compulsory for British children in 1853, then 1902 in France. But comes just before a most famous discovery, that of the rabies vaccine by Louis Pasteur. The first injection carried out on a child, bitten by a dog suspected of being rabid, was a success in 1885. This vaccine, however, was different from that against smallpox: it was developed from a attenuated strain of virus. A few years will suffice to see the appearance of that against tuberculosis, diphtheria, tetanus and whooping cough.

After killing 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 like the best medicine in the world, it is also the source of distrust. So much so that according to a survey Odoxa-Dentsu Consulting for franceinfo and Le Figaro published on November 12, 2020, 50% of French people surveyed (1,005 people) would refuse to be vaccinated against Covid-19 if a vaccine was soon deployed in France.

But how does a vaccine work?

To understand vaccination, let’s first 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 again confronted with this pathogen, these fighting cells are reactivated to eliminate the intruder as quickly as possible and not to suffer from the pathology for which he is responsible.

It is on this same principle that vaccination is based. Made from small amounts of bacteria or viruses (weakened or dead, so that they lose their dangerousness) and injected into the body, vaccines trigger the production of “memory” cells. The body develops, without causing the disease, a “stock” of antibodies. It will thus be best prepared in contact with pathogens. This is ultimately what is called theimmunity to disease, and the goal of all vaccines. The duration of their protection varies. This is why reminders are sometimes necessary to reactivate it.

What about collective immunity in all of this?

Collective immunity corresponds to a percentage of people, in a population, possessing antibodies to an infectious agent. Once this level is reached – by exposing individuals or protecting them with a vaccine – the virus or bacteria no longer circulates and the epidemic stops. This threshold depends on each pathology. Against the measles, it is obtained when about 95% of a population is immune. The rest (remaining 5%) is protected, as the disease no longer spreads. The papillomavirus is also a good example (see video at the top 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 worry: whether 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 been long awaited.

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