Vaccines are drugs designated to develop active immunity in the organism of vaccinated humans and animals. The main activator of each vaccine is an immunogen, i.e. a corpuscular or dissolved substance bearing chemical structures similar to components of the causative agent responsible for the production of immunity.
Depending on the nature of the immunogen vaccines can be divided into:
- whole-cell vaccines consisting of bacteria or viruses that remain entire during production;
- chemical vaccines from metabolic products of microorganisms (the classical example includes toxoids) or their integral components, so called subunit vaccines;
- genetically engineered vaccines containing individual gene expression products of the microorganism deposited in special cell systems;
- chimeric, or vector-based, vaccines, where the gene controlling the protective protein synthesis is imbedded in a harmless microorganism with a view to the protein synthesis in the vaccinated organism, and, finally,
- synthetic vaccines using as an immunogen a chemical analog of the protective protein obtained by direct chemical synthesis.
Further, whole-cell vaccines are divided into inactivated, or killed, and live attenuated vaccines. In inactivated ones the microorganism’s ability to develop its pathogenic properties is effectively eliminated by chemical, thermal or other treatment of the microbial (viral) suspension, in other words, by killing the pathogenic agent with the preservation of its immunization activity; in attenuated ones – by deep and stable changes in the microorganism’s genome that exclude the possibility of its return to the virulent phenotype, i.e. to reversion. In the end, effectiveness of live vaccines is determined by the ability of the attenuated microorganism to replicate in the vaccinated organism, producing immunologically active components directly in its tissues. For killed vaccines, the immunizing effect depends on the quantity of immunogens administered with the drug, so to create more effective immunogenic stimuli the concentration and purification of microbial cells and viral particles are required. The immunizing ability of inactivated and all other non-replicating vaccines can be increased by sorption of immunogens on large molecular chemically inert polymers, adding of adjuvants, i.e. substances that induce immune reactions of the organism, and enclosure of immunogens into tiny capsules that are slowly dissolved contributing to the deposit of vaccines in the place of administration and prolonging the action of the immune stimuli.
Vaccine components
It is known that each vaccine is based on protective antigens, which constitute only a small part of a bacterial cell or a virus and ensure the development of the immune response. Protective antigens can be proteins, glycoproteins, lipopolysaccharide-protein complexes. They can be bound to microbial cells (pertussis bacillus, streptococcus, etc.) or released by them (bacterial toxins); in viruses they are generally located in superficial layers of viral supercapsids.
In addition to the main active ingredient, vaccines can include other components: sorbents, preservatives, fillers, stabilizers and non-specific impurities. Such impurities can include substrate proteins remained after the cultivation of viral vaccines, trace quantity of antibiotics and animal serum proteins used in some cases for the cultivation of cell cultures. (* – the trace quantity is an amount which cannot be detected by current methods). Preservatives are included in vaccines wherever they are produced. They are used to ensure sterility of drugs in cases when bacterial contamination becomes possible (formation of micro cracks during transportation, storage in the open primary multidose package). The instruction to add preservatives is contained in the WHO’s recommendations. As for the substances used as stabilizers and fillers, only those which have been approved for administration in humans are used in the production of vaccines.
Vaccination and revaccination
Vaccination can be single (measles, mumps, tuberculosis) or multiple (poliomyelitis, TDaP). This indicates the number of vaccinations required to obtain the immunity.
Revaccination is designated to maintain the immunity developed as a result of the previous vaccinations. It is usually conducted several years after vaccination.
Effectiveness of vaccination
Post-vaccination immunity is the immunity developed after vaccination. Vaccination is not always effective. Vaccines can lose their properties if not properly stored. But even if storage conditions are met, there is always a probability that the immunity will not be stimulated.
Bacteriophages are viruses selectively infecting bacterial cells. As a rule, bacteriophages replicate inside bacteria causing their lysis.
The ability to study phages as antimicrobial agents in the clinic attracts the attention of the world’s medical and scientific community. The rapid spread of mutant harmful bacterial strains multi-resistant to antibiotics has sparked the interest of the scientific community to this method having almost a 100-year history.
Modern biological technologies allow the use of bacteriophage therapy against most bacterial infections. At present, bacteriophage drugs have been created. The history of mass use of these drugs dates back to the tragic dates of the Great Patriotic War (a mixture of several types of bacteriophages fighting against bacteria causing severe wound infections was invented in 1940).
These drugs saved the life of thousands of wounded soldiers. This experience contributed to the preservation and development of the biopharmaceutical production of bacteriophages in Russia – today this country is the world’s leader in the production of these antibacterial drugs.
In the 30s of the last century, a large American concern even founded a clinic that started to treat with phages. Advocates of the new method promised healing of all illnesses. However, the reality left much to be desired: the scientific foundations of the therapy were so scarce that the new drug was administered almost blindly. It was considered that all phages are identic and can win any bacteria. Different diseases were treated with the same phages, but the sick persons were not healed – so, the method was seriously discredited. The opinion that phages are not sufficiently effective remained in the medical community for many years and it is still maintained.
Recently, researchers from the Rockefeller University in New York made some publications describing successful phage therapy.
Blood products are drugs derived from blood. There are preparations of complex action, immunologically active (immunoglobulins) and hemostatic preparations.
