Adverse events: Causes

Vaccines contain different components to make them effective. However, each component in a vaccine adds a potential riskVaccine-associated riskThe probability of an adverse or unwanted outcome occurring, and the severity of the resultant harm to the health of vaccinated individuals in a defined population, following immunization with a vaccine under ideal conditions of use. of an adverse reactionVaccine reaction (also referred to as adverse vaccine reaction or adverse reaction)A classification of AEFI referring to events caused or precipitated by the vaccine when given correctly, caused by the inherent properties of the vaccine.. Regulatory authorities must ensure that all vaccine components, singly and in combination, do not compromise vaccine safety.

Vaccines are prepared with different types of antigens, using different scientific methods such as attenuation, inactivation, and recombination DNA technology.

Some vaccines include components to enhance immune response, such as adjuvants and conjugated proteins.

Vaccines can also include antibioticsAntibioticA substance that kills or inhibits the growth of bacteria. Antibiotics (in trace amounts) are used during the manufacturing phase of some vaccines to prevent bacterial contamination of the tissue culture cells., stabilizersStabilizersCompounds that are used to help vaccine maintain its effectiveness during storage. Vaccine stability is essential, particularly where the cold chain is unreliable. Factors affecting stability are temperature and pH., and preservativesPreservativesCompounds that are added to multi-dose vaccine vials to prevent bacterial and fungal growth. The most commonly used product is called thiomersal, a mercury-containing compound. to reduce contamination during the manufacturing process and to maintain their effectivenessVaccine effectivenessThe probability that a vaccine, when used in the field under routine vaccination circumstances, confers immunity in a population. Expressed as a percent. during transport and storage.

Please note that routes of administration (intradermal, subcutaneous or intramuscular injection, drops given orally, or intranasal administration) also contribute to the risk of an adverse reaction: They are recommended by the manufacturer for each vaccine and are determined to maximize vaccine effectiveness and limit adverse reactions.