Vaccination: how it works
Ivan Konovalov, Post-science
The word "vaccine" comes from vacca ("cow"): this is due to the fact that the vaccination era was opened by vaccination against smallpox, which was created on the basis of cowpox. People realized that, having had cowpox, a person acquires immunity against smallpox — a much more terrible and serious disease. Based on this knowledge, Edward Jenner developed his vaccine. This first vaccine was created exclusively experimentally, but today people have managed, while maintaining the general principle of vaccine operation, to switch to much more modern technological platforms, purifying vaccines and providing a higher level of safety and knowledge of their composition and the concentration of those microorganisms that are used in them.
The history of the vaccine: from cowpox to the latest drugs
The period from the end of the XVIII to the XX century was characterized in many ways by incredibly rapid development, in particular, microbiology, which was divided into virology and bacteriology. This made it possible to control viruses and bacteria by creating inactivated vaccines. The development of chemistry predetermined the possibility of creating bacterial vaccines, some of which were alive — for example, a weakened vaccine against tuberculosis is among them. The bacillus of tuberculosis of Calmet and Guerin has undergone such a large number of changes that, being vaccinated to a newborn child, leaves only a local infectious process — some then have a scar on their shoulder for the rest of their lives. This is an example of how we infect a child with a controlled vaccine and thereby save him from severe forms of the disease.
The development of immunology is, of course, the greatest achievement of the XX–XXI centuries: during this time, our understanding of many mechanisms of both the infectious process and the formation of protection against certain infections has fundamentally changed. This made it possible to create rational vaccines to achieve very specific goals. That is why it is impossible to compare vaccination against smallpox and vaccination against a new type of coronavirus infection based on unreplicable adenovirus vectors. Nevertheless, the words "vaccination" and "vaccine" remain commonly used terms, although the first vaccines and the latest drugs are radically different.
The study of the mechanisms of the immune response made it possible to divide immunoprophylaxis into passive and active. With passive immunoprophylaxis, a person is injected with any components, for example, donor blood, which have protective properties, for example, donor human immunoglobulin. Now technologies allow us to create highly purified monoclonal antibodies, which are also used in the treatment of certain diseases, not always infectious: sometimes they treat a number of oncological diseases. To date, various mixtures of monoclonal antibodies are also used in the treatment of a new type of coronavirus infection, which allow, if they were introduced at an early date, to have a very beneficial effect on the further course of infection. An example of the formation of passive immunity is also the transfer of antibodies from the mother to her newborn child: in this case, there is a certain protection of the newborn from infections such as influenza or measles, for about the first 3-6 months, depending on how many antibodies the mother had. That is why, in some cases, a pregnant woman is vaccinated so that she transfers protection to her child, who cannot receive these vaccinations yet.
Active immunity is the development of protection in one form or another, either naturally, in particular as a result of an infectious disease, or by vaccination. In fact, vaccination is the training of the immune system by the introduction of certain substances, usually of an antigenic structure, to create two main lines of defense. First, active immunity involves the circulation of antibodies that should protect against infection. After an infectious disease, not all types of antibodies are protective (for example, a person with HIV infection has a lot of antibodies, but unfortunately they do not protect him from the disease itself): vaccination aims to create a very intense and very isolated type of immune response. Secondly, vaccination trains our immunological memory cells. White cells, in particular leukocytes and lymphocytes, are not only engaged in the destruction of infected cells and various pathogens, but also train by transmitting signals to other Beta cells, which, in turn, produce antibodies.
Vaccination history
Even before the creation of the first vaccine, there was a variolation that was described in Ancient China. What is it? From a person who had smallpox, the contents of smallpox pustules were taken and injected in a certain concentration to a healthy person who had not yet had smallpox, thus trying to control the amount of infection entering the body. Unfortunately, this method led to a fairly large number of deaths, but even royals often vaccinated themselves and their children.
The revolutionary experience that was recorded by Edward Jenner when creating a smallpox vaccine, of course, was observed before that, but it was not systematized and described. This is what distinguishes the creation of a vaccine from the rumor that milkmaids who often come into contact with cows with cowpox often have scars from pustules on their hands, but they very rarely get sick with smallpox. In the future, the vaccine was very quickly used throughout the enlightened world, primarily in Europe. Infection does not choose people: poor or rich, it can kill anyone, and therefore, when a much safer method of vaccination than variolation appeared, this method of prevention began to spread very quickly.
The Russian Empire, having close ties with Europe, quickly introduced smallpox vaccination, but it was of an individual nature, because, as with other types of medical care, not all people could afford it. The social stratification in terms of the availability of a particular medical care at that time was much greater than it is today. But people saw that a huge number of people simply do not survive after infection, and a number of socially-oriented countries, such as the young Soviet Union, could afford to establish decrees on mandatory smallpox vaccination and keep records of those people who received or did not receive vaccination. Partial vaccination has a very small effect on population infectious processes: if the infection continues to develop, vaccinations in individuals do not allow achieving population immunity. If the infection is contagious enough, then even with the vaccine, people will continue to get sick.
Immunoprophylaxis and the animal world
Very big breakthroughs in immunology and immunoprophylaxis were associated with the need to save livestock. Just 150-200 years ago, the average human life was worth much less than the life of a horse or a cash cow. Since a number of diseases are inherent in animals, the organization of mass immunoprophylaxis among animals was carried out much more aggressively.
The creation of vaccines for animals to some extent limited the spread of infections among humans - for example, leptospirosis or plague, individual outbreaks of which are noted in some regions bordering the territory of the Russian Federation, where infection occurs when eating thermally unprocessed meat or when deboning animal carcasses, for example through micro—wounds on the skin of hunters' hands. Thus, if we control the infectious process among the livestock of animals, we will actually stop its spread among the human population. This is convenient because some vaccines in animals may work better than their corresponding analogues in humans.
Some animal organisms are used to create drugs that form passive immunity, such as hyperimmune serums. An example is the vaccination of horses, from whose blood tetanus serum is created. On the other hand, a person can also be used as a laboratory for the production of antibodies: donor human immunoglobulins are used, for example, for emergency prevention of measles in the unvaccinated. This method is resorted to if we cannot vaccinate a person with a live vaccine due to a severe immunodeficiency condition, if it is necessary to protect a pregnant woman from measles, or if we are talking about a child in the first months of his life, when vaccination with live measles vaccines is also not carried out.
Vaccination and life expectancy
Vaccination and access to clean water are the two main factors that have affected human life expectancy. Vaccines against whooping cough and measles marked the fundamental elimination of mortality from these infections. About 100-150 years ago, especially in large families, an outbreak of whooping cough could take the lives of 15 to 35% of those infected, whereas now deaths from these infections, primarily among children, have become extremely rare. Of course, this mortality rate was partly due to the lower availability of medical care and the lack of targeted therapy, primarily antibacterial drugs. It was also influenced by a lack of understanding of the basics of sanitary and hygienic standards and a shortage of calories and protein in this diet. Nevertheless, when we observe a decrease in vaccination coverage even for a short time, outbreaks of seemingly long-forgotten infections immediately begin en masse.
An example is the experience of post—war Japan, when the mass use of whole-cell pertussis vaccine was often accompanied by complications - excessive fever in a child and the formation of seizures. By the end of the 1970s, mass refusals to vaccinate Japanese residents formed a trend towards the abolition of mandatory vaccination against whooping cough, which was temporarily supported by the Japanese Ministry of Health. Within literally one to one and a half years, the incidence of whooping cough jumped sharply, because during this time a large number of children were born who had no immunity, and those who were not vaccinated on time began to attend collectives and thus actively bring infection to young children, and whooping cough in a child under a year often ends in death. Literally a few years after the start of such a socially approved experiment on the health of the nation, the authorities began to carry out universal vaccination, and within three to five years the situation was fixed at the level of morbidity before the vaccination was canceled.
The rapid development of immunology and the study of infectious diseases in just a few hundred years have allowed people to fundamentally change their outlook on life. A number of deadly infections as the main diseases and causes of death have receded to the second, third, fourth plan, but the infections themselves have not gone away. It should be understood that vaccination is the only way to keep the life of humanity in the form in which we are used to seeing it.
About the author: Ivan Konovalov – Candidate of Medical Sciences, Associate Professor of the Department of Infectious Diseases in Children of the N.I. Pirogov PF RNIMU of the Ministry of Health of Russia.
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