Vaccines

Composition of a Vaccine Preparation

Any vaccine is a complex immunobiological system. In addition to the main active substance (the specific antigen), preparations contain auxiliary components that depend on the formulation:

• Stabilizers. Protect the antigen from degradation during manufacturing and long-term storage. Examples include sucrose-agar-gelatin mixtures or homologous proteins (e.g., human albumin).
• Preservatives. Ensure the sterility of the solution and inhibit the growth of accidental microflora. Formalin, thimerosal (at a 1:10,000 dilution), and other antimicrobial agents are used for this purpose.
• Adjuvants. Substances that nonspecifically enhance the immunogenicity of the administered antigen, prompting the body to mount a stronger immune response.

Live-Attenuated Vaccines

The active principle here consists of attenuated (weakened) strains of microorganisms. They are entirely devoid of virulence (unable to cause disease) but retain specific antigenicity.

Methods of pathogen attenuation:

1. Chemical — treatment with mutagens.
2. Physical — exposure to radiation or temperature.
3. Biological — serial passages of the pathogen through cell cultures, chicken embryos, or the bodies of non-susceptible animals.

The core mechanism of a live vaccine is that microorganisms with residual virulence replicate within the human body. This safely mimics a natural infection and leads to robust immunity. These preparations are dosed by the number of live microbial cells or viral particles and are typically administered as a single dose (e.g., vaccines against measles, rubella, mumps, and poliomyelitis).

In addition to classical attenuated strains (originally proposed by Pasteur), divergent strains are used—microbes related to human pathogens but safe for humans (e.g., Mycobacterium bovis BCG, vaccinia virus). There are also vector vaccines, in which genes encoding protective antigens are engineered into the genome of a safe carrier (such as the vaccinia virus or Salmonella).

Inactivated (Killed) Vaccines

These preparations contain no live pathogens. They are divided into two main groups:

• Whole-cell / Whole-virion: contain entirely killed bacteria or viruses.
• Subcellular / Subvirion: contain only extracted complexes bearing the necessary protective antigens (proteins, glycoproteins, lipopolysaccharides).

Inactivation of microbes is achieved via chemical (phenol, alcohol, formaldehyde) or physical methods (ionizing radiation, UV irradiation, heating). To isolate antigens for subunit vaccines, enzymatic treatment, phenol extraction, ultracentrifugation, isoelectric precipitation, chromatography, and ultrafiltration are employed.

Unlike live vaccines, inactivated vaccines are dosed in antigenic units. They frequently include mandatory adjuvants and preservatives. They are administered parenterally (intramuscularly or subcutaneously), and establishing reliable immunity requires a series of multiple injections.

Safety Requirements and Contraindications

Before entering mass clinical use, a preparation must meet strict criteria. Modern principles dictate that regardless of whether a vaccine is live or inactivated, the primary goal is maximum protective efficacy (reduction in morbidity) without compromising patient safety.

Biological requirements:

• High immunogenicity.
• Low reactogenicity (absence of severe adverse reactions).
• Genetic stability of vaccine strains.
• Absence of oncogenic, allergenic, and teratogenic (fetal-damaging) properties.

Contraindications (medical exemptions) are established to prevent post-vaccination complications. General medical exemptions include acute infectious and non-infectious diseases, severe immunodeficiencies, severe cardiovascular pathologies, malignancies, chronic parenchymal organ diseases, central nervous system disorders, and allergic conditions. Local reactions (hyperemia, edema) or transient fever within normal limits do not constitute a reason to withhold further vaccinations.

Regulatory Framework and Immunization Schedules

Immunization is regulated by national public health legislation and National Immunization Schedules.

The schedules define age-based vaccination algorithms. Mandatory lists for children and adults typically include vaccinations against tuberculosis, hepatitis B, poliomyelitis, pertussis, diphtheria, tetanus, measles, rubella, and mumps. Additional vaccinations are administered based on epidemiological indications (e.g., influenza) or when traveling to regions endemic for highly dangerous infections.