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What are vaccines and what are they?
Last reviewed: 06.07.2025
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For specific prevention of infectious diseases, vaccines are used that allow the formation of active immunity before natural contact with the pathogen.
Vaccines intended for the prevention of one infection are called monovaccines, against two - divaccines, against three - travovaccines, against several - polyvaccines. Associated vaccines are those containing a mixture of antigens of various microorganisms and anatoxins. Polyvalent vaccines are those that include several varieties of serological types of pathogens of one infection (leptospirosis, colibacillosis, salmonellosis, pseudomonosis of minks, Marek's disease, etc.).
Various types of vaccines are used for the immunoprophylaxis of infectious diseases.
Live vaccines
They are a suspension of vaccine strains of microorganisms (bacteria, viruses, rickettsia) grown on various nutrient media. Usually, strains of microorganisms with weakened virulence or deprived of virulence properties, but fully retaining immunogenic properties, are used for vaccination. These vaccines are produced on the basis of apathogenic pathogens, attenuated (weakened) in artificial or natural conditions. Attenuated strains of viruses and bacteria are obtained by inactivating the gene responsible for the formation of the virulence factor, or by mutations in genes that non-specifically reduce this virulence.
In recent years, recombinant DNA technology has been used to produce attenuated strains of some viruses. Large DNA viruses, such as the smallpox virus, can serve as vectors for cloning foreign genes. Such viruses retain their infectivity, and the cells they infect begin to secrete proteins encoded by the transfected genes.
Due to the genetically fixed loss of pathogenic properties and the loss of the ability to cause an infectious disease, vaccine strains retain the ability to multiply at the injection site, and later in regional lymph nodes and internal organs. Vaccine infection lasts for several weeks, is not accompanied by a pronounced clinical picture of the disease and leads to the formation of immunity to pathogenic strains of microorganisms.
Live attenuated vaccines are obtained from attenuated microorganisms. Attenuation of microorganisms is also achieved by growing cultures under unfavorable conditions. Many vaccines are produced in dry form in order to increase shelf life.
Live vaccines have significant advantages over killed vaccines, due to the fact that they completely preserve the antigen set of the pathogen and provide a longer state of immunity. However, given the fact that the active principle of live vaccines are living microorganisms, it is necessary to strictly observe the requirements that ensure the preservation of the viability of microorganisms and the specific activity of vaccines.
Live vaccines do not contain preservatives; when working with them, it is necessary to strictly adhere to the rules of asepsis and antisepsis.
Live vaccines have a long shelf life (1 year or more) and are stored at a temperature of 2-10 C.
5-6 days before the administration of live vaccines and 15-20 days after vaccination, antibiotics, sulfonamides, nitrofuran drugs and immunoglobulins cannot be used for treatment, as they reduce the intensity and duration of immunity.
Vaccines create active immunity in 7-21 days, which lasts on average up to 12 months.
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Killed (inactivated) vaccines
To inactivate microorganisms, heating, formalin, acetone, phenol, ultraviolet rays, ultrasound, and alcohol are used. Such vaccines are not dangerous, they are less effective than live ones, but when administered repeatedly, they create a fairly stable immunity.
In the production of inactivated vaccines, it is necessary to strictly control the inactivation process and at the same time preserve the set of antigens in the killed cultures.
Killed vaccines do not contain live microorganisms. The high efficiency of killed vaccines is due to the preservation of a set of antigens in inactivated microorganism cultures that provide an immune response.
For high efficiency of inactivated vaccines, the selection of production strains is of great importance. For the production of polyvalent vaccines, it is best to use strains of microorganisms with a wide range of antigens, taking into account the immunological affinity of various serological groups and variants of microorganisms.
The spectrum of pathogens used to prepare inactivated vaccines is very diverse, but the most widely used are bacterial (vaccine against necrobacteriosis) and viral (anti-rabies inactivated dry culture vaccine against rabies from the Shchyolkovo-51 strain).
Inactivated vaccines should be stored at 2-8 °C.
Chemical vaccines
They consist of antigen complexes of microbial cells combined with adjuvants. Adjuvants are used to enlarge antigen particles and to increase the immunogenic activity of vaccines. Adjuvants include aluminum hydroxide, alum, organic or mineral oils.
The emulsified or adsorbed antigen becomes more concentrated. When introduced into the body, it is deposited and enters the organs and tissues from the injection site in small doses. Slow resorption of the antigen prolongs the immune effect of the vaccine and significantly reduces its toxic and allergic properties.
Chemical vaccines include deposited vaccines against swine erysipelas and swine streptococcosis (serogroups C and R).
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Associated vaccines
They consist of a mixture of cultures of microorganisms that cause various infectious diseases, which do not suppress each other's immune properties. After the introduction of such vaccines, immunity against several diseases is formed in the body at the same time.
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Anatoxins
These are preparations containing toxins that are devoid of toxic properties but retain antigenicity. They are used to induce immune reactions aimed at neutralizing toxins.
Anatoxins are produced from exotoxins of various types of microorganisms. To do this, toxins are neutralized with formalin and kept in a thermostat at a temperature of 38-40 °C for several days. Anatoxins are essentially analogs of inactivated vaccines. They are purified from ballast substances, adsorbed and concentrated in aluminum hydroxide. Adsorbents are introduced into the anatoxin to enhance adjuvant properties.
Anatoxins create antitoxic immunity that lasts for a long time.
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Recombinant vaccines
Using genetic engineering methods, it is possible to create artificial genetic structures in the form of recombinant (hybrid) DNA molecules. A recombinant DNA molecule with new genetic information is introduced into the recipient cell using carriers of genetic information ( viruses, plasmids), which are called vectors.
The production of recombinant vaccines involves several stages:
- cloning of genes that ensure the synthesis of necessary antigens;
- introduction of cloned genes into a vector (viruses, plasmids);
- introduction of vectors into producer cells (viruses, bacteria, fungi);
- in vitro cell culture;
- isolation of the antigen and its purification or use of producer cells as vaccines.
The finished product must be tested in comparison with a natural reference drug or with one of the first series of a genetically engineered drug that has passed preclinical and clinical trials.
B. G. Orlyankin (1998) reports that a new direction in the development of genetically engineered vaccines has been created, based on the introduction of plasmid DNA (vector) with an integrated gene of a protective protein directly into the body. In it, plasmid DNA does not multiply, does not integrate into chromosomes and does not cause a reaction of antibody formation. Plasmid DNA with an integrated genome of a protective protein induces a full-fledged cellular and humoral immune response.
Various DNA vaccines can be constructed on the basis of one plasmid vector, changing only the gene encoding the protective protein. DNA vaccines have the safety of inactivated vaccines and the effectiveness of live ones. Currently, more than 20 recombinant vaccines have been constructed against various human diseases: a vaccine against rabies, Aujeszky's disease, infectious rhinotracheitis, viral diarrhea, respiratory syncytial infection, influenza A, hepatitis B and C, lymphocytic choriomeningitis, human T-cell leukemia, human herpesvirus infection, etc.
DNA vaccines have a number of advantages over other vaccines.
- When developing such vaccines, it is possible to quickly obtain a recombinant plasmid carrying a gene encoding the necessary pathogen protein, in contrast to the lengthy and expensive process of obtaining attenuated strains of the pathogen or transgenic animals.
- Technological efficiency and low cost of cultivating the obtained plasmids in E. coli cells and its further purification.
- The protein expressed in the cells of the vaccinated organism has a conformation that is as close as possible to the native one and has high antigenic activity, which is not always achieved when using subunit vaccines.
- Elimination of the vector plasmid in the body of the vaccinated person occurs within a short period of time.
- With DNA vaccination against particularly dangerous infections, the probability of developing the disease as a result of immunization is completely absent.
- Prolonged immunity is possible.
All of the above allows us to call DNA vaccines the vaccines of the 21st century.
However, the idea of complete infection control through vaccines persisted until the late 1980s, when it was shaken by the AIDS pandemic.
DNA immunization is also not a universal panacea. Since the second half of the 20th century, pathogens that cannot be controlled by immunoprophylaxis have become increasingly important. The persistence of these microorganisms is accompanied by the phenomenon of antibody-dependent enhancement of infection or integration of the provirus into the genome of the macroorganism. Specific prophylaxis can be based on inhibition of pathogen penetration into sensitive cells by blocking recognition receptors on their surface (viral interference, water-soluble compounds that bind receptors) or by inhibiting their intracellular reproduction (oligonucleotide and antisense inhibition of pathogen genes, destruction of infected cells by a specific cytotoxin, etc.).
The problem of provirus integration can be solved by cloning transgenic animals, for example, by obtaining lines that do not contain the provirus. Therefore, DNA vaccines should be developed for pathogens whose persistence is not accompanied by antibody-dependent enhancement of infection or preservation of the provirus in the host genome.
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Seroprophylaxis and serotherapy
Serums form passive immunity in the body, which lasts for 2-3 weeks, and are used to treat patients or prevent diseases in a threatened area.
Immune serums contain antibodies, so they are most often used for therapeutic purposes at the onset of the disease in order to achieve the greatest therapeutic effect. Serums can contain antibodies against microorganisms and toxins, so they are divided into antimicrobial and antitoxic.
Serums are obtained at biofactories and bio-complexes by means of two-stage hyperimmunization of immune serum producers. Hyperimmunization is carried out with increasing doses of antigens (vaccines) according to a certain scheme. At the first stage, the vaccine is administered (1-2 times), and then according to the scheme in increasing doses - a virulent culture of the production strain of microorganisms over a long period of time.
Thus, depending on the type of immunizing antigen, antibacterial, antiviral and antitoxic serums are distinguished.
It is known that antibodies neutralize microorganisms, toxins or viruses mainly before they penetrate into target cells. Therefore, in diseases where the pathogen is localized intracellularly (tuberculosis, brucellosis, chlamydia, etc.), it has not yet been possible to develop effective methods of serotherapy.
Serum therapeutic and prophylactic drugs are used mainly for emergency immunoprophylaxis or elimination of certain forms of immunodeficiency.
Antitoxic serums are obtained by immunizing large animals with increasing doses of antitoxins, and then toxins. The resulting serums are purified and concentrated, freed from ballast proteins, and standardized by activity.
Antibacterial and antiviral drugs are produced by hyperimmunization of horses with the corresponding killed vaccines or antigens.
The disadvantage of the action of serum preparations is the short duration of the passive immunity formed.
Heterogeneous serums create immunity for 1-2 weeks, homologous globulins for 3-4 weeks.
Methods and order of administration of vaccines
There are parenteral and enteral methods of introducing vaccines and serums into the body.
With the parenteral method, drugs are administered subcutaneously, intradermally and intramuscularly, which allows bypassing the digestive tract.
One of the types of parenteral administration of biological preparations is aerosol (respiratory), when vaccines or serums are administered directly into the respiratory tract by inhalation.
The enteral method involves the administration of biopreparations through the mouth with food or water. This increases the consumption of vaccines due to their destruction by the mechanisms of the digestive system and the gastrointestinal barrier.
After the introduction of live vaccines, immunity is formed in 7-10 days and lasts for a year or more, and with the introduction of inactivated vaccines, the formation of immunity ends by the 10-14th day and its intensity lasts for 6 months.