Adverse effects and vaccine reactogenicity
Any immunization may be accompanied by adverse effects, which should not be confused with true complications. Common manifestations include general malaise, local reactions, and a moderate increase in body temperature. Much less common are headaches, joint pain, sleep disturbances, vomiting, and fainting.
The etiology of such conditions is associated either with the presence of impurities in the preparations or with the action of pro-inflammatory factors that are physically inseparable from the active antigen. A prime example is the high reactogenicity of the whole-cell DTaP vaccine, which is directly linked to the pertussis component.
To reduce the frequency of adverse effects, acellular preparations with reduced reactogenicity are used (for example, Infanrix or Pentaxim, which additionally protects against poliomyelitis and Haemophilus influenzae type b). They contain only purified subcapsular antigens: pertussis toxoid, filamentous hemagglutinin, and pertactin. In addition, the body's reactogenicity changes with age; thus, for diphtheria revaccination in children over 6 years of age, exclusively toxoid with a reduced antigen content (Td) is used.
Classification of post-vaccination complications
Unlike expected adverse reactions, complications represent more severe consequences of vaccination. There are three main groups of post-vaccination complications:
- Toxic.
- Allergic.
- Nervous system lesions.
A separate category is the post-vaccination infectious process. It can develop when using live attenuated vaccines (BCG, OPV, measles, rubella, and mumps preparations) containing a weakened but viable strain of the pathogen.
To eliminate the risks of vaccine-associated complications in closed children's institutions (orphanages, boarding schools, anti-tuberculosis sanatoriums), children are vaccinated according to special indications. For example, instead of the live vaccine, they are administered the inactivated polio vaccine (IPV) in a three-dose schedule.
Contraindications to immunization
To minimize the risk of developing severe consequences, the physician is obliged to strictly rule out contraindications before administering the preparation. These include:
- Presence of immunodeficiency states.
- Severe reactions or documented complications following a previous administration of a similar vaccine.
- Allergy to any components of the vaccine preparation.
It is important to consider the composition of a specific vaccine. For example, live attenuated measles, rubella, and mumps vaccines may contain antibiotics and stabilizers. The liquid recombinant hepatitis B vaccine includes an aluminum hydroxide adjuvant and a merthiolate preservative. Hypersensitivity to these excipients is a strict medical contraindication.
Normal reaction or complication? (using measles as an example)
Sometimes the regular course of the vaccine process is mistaken for a complication. During routine immunization against measles with a live vaccine, a specific post-vaccination reaction may develop in a child on the 6th–15th day after injection.
It manifests as short-term fever, catarrhal syndrome, and sometimes a measles-like rash. Clinically, this is regarded as a variant of the normal course of the infectious process caused by the attenuated virus. The main epidemiological feature of this condition: regardless of the severity of symptoms, the vaccinated patient is completely non-contagious to others.
For quick memorization of the three groups of severe complications, use the acronym TAN: Toxic, Allergic, Nervous system disorders.
Class and exam questions
How does an adverse effect differ from a post-vaccination complication?
Adverse effects (fever, malaise, local reactions) are common and resolve on their own. Complications (toxic, allergic, neurological) are severe pathologies occurring in isolated cases (approximately 1:1,000,000).
Why are antiviral vaccines administered only 12–15 months after birth?
Such a delay is necessary to prevent the neutralization of the vaccine preparation by maternal antibodies present in the child's blood serum during the first months of life.
How to reduce the risk of complications in closed children's groups?
In boarding schools and orphanages, inactivated preparations (e.g., IPV instead of the live oral polio vaccine) are used to completely eliminate the risk of developing vaccine-associated infections within the community.
What are the existing routes of vaccine administration and how do they affect safety?
The main route of administration is subcutaneous, less frequently intramuscular. Mucosal preparations (oral, nasal) are currently under development, which could potentially change the safety profile. Doses and intervals between injections are strictly regulated to minimize any risks.
What else to study on this topic
- Types of vaccine preparations: live, inactivated, toxoids, and recombinant
- National Immunization Schedule and routine vaccination timelines
- Specific prevention and anti-epidemic measures in a measles focus
- Congenital and acquired rubella: pathogenesis and "catch-up" immunization strategy
- Features of whole-cell and acellular vaccines (DTaP, Pentaxim, Infanrix)
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