Vaccines: between benefits and concerns

摘要

The evolution of medicine is strongly related to technological progresses and to vaccines that increased the life expectancy during the last century. The appearance of vaccines represented a true revolution in medicine. The principle of vaccination has been stated by Louis Pasteur in 1881 and is very simple: the exposure to an attenuated form of the disease to prevent a more severe form. Pasteur has discovered the first attenuated artificial vaccine, represented not by a microorganism similar to that causing the disease, but from the same strain having lost its virulence. The history of vaccination begins in the 18 th century, with the monography of Edward Jenner, but there are cases in history that prepared the development of preventive medicine. Mithridates, the king of Pontus, conquered by Romans, wanted to suicide by ingestion of poison. His two daughters died after drinking the poison, but Mithridates survived and asked one of his people to kill him with a sword. His survival after poisoning was linked to the daily usage of certain drugs, which protected him against an otherwise deadly dose of poison. This legend explains the biological phenomenon of habituation by ingestion of progressive doses of poison. Since historical times, it is known that certain infectious diseases (like plague) can not appear twice in humans. The discovery of vaccines led to important changes of public health policies. In 1908, Bacille de Calmette et Guerin (BCG) was discovered, as consequence of accumulated knowledge on tuberculosis. Once the safety of BCG and its protective effects have been demonstrated in animals, human vaccination against tuberculosis was imposed after the First World War, when tuberculosis was responsible for 20-40% of deaths. Nowadays, tuberculosis is still an important public health issue in developing countries, with an increasing number of cases also in developed countries, explained mainly by the multi-resistance to antibiotics. The BCG vaccination remains an effective preventive measure, inexpensive, and with limited side effects. The flu has been known since ancient times and it is caused by an RNA virus. In the 14 th century it was called influenza. Influenza can be epidemic or pandemic. Epidemic influenza occurs every year during winter, when more severe pandemic influenza occurs several times a century. The most severe influenza pandemic appeared in Spain, between 1918-1919, and was responsible for 50-100 million deaths worldwide, the most lethal health disaster of all time, comparable to the black plague between 1347-1350. Nowadays, the influenza vaccines can prevent the influenza pandemics. During the last years, because the most severe epidemics have disappeared or are in course of disappearance, it is increasingly difficult to convince the population (especially from developed countries) about the necessity to get vaccinated against a risk that may be considered minor. Moreover, the fear of side effects, stimulated by a part of mass media, led to a decrease of vaccination rate, which explains the recent appearance of cases of measles or diphtheria. Since their apparition, vaccines have been a matter of debate. The risks associated to vaccination are better accepted when the fear of a certain infectious disease is great. In this context, the role of mass media is very important, because when alarmist information regarding a certain vaccine is announced, a certain part of the population understand that it is better to refrain from getting the vaccine. Moreover, the anti-vaccines movement sustains that scientific publications concerning vaccinations are controlled by governments and pharmaceutical companies, who underestimate the side effects of vaccinations. The success of vaccination is based on a double confidence: confidence in the safety of the vaccine (guaranteed by doctors and governments) and confidence in the need for vaccination. To obtain this confidence, it is of utmost importance to intensify the mass education for health, by healthcare professionals who must educate and motivate the population. COVID-19 pandemics put the entire world on pressure and fear. This new viral disease does not have a specific treatment until now, only the current restrictions being able to prevent more people from being infected or dying. A vaccine could be the only solution to fight the pandemics and the best exit strategy, but the population needs to be properly informed and educated.