Vaccine safety and adverse events following immunization
Vaccines are designed to provoke a reaction in the body's immune system that in turn provides protection from the disease(s) against which the vaccine is given. In addition to this desired reaction, all vaccines produce some degree of unwanted reaction. The term reaction denotes any such unwanted (or adverse) effect that is caused by the vaccine. The vast majority of these reactions are trivial and harmless. Some are more noticeable and annoying. A very small number are serious and potentially life threatening
In contrast the term adverse event following immunization (AEFI) is defined as a medical incident that takes place after an immunization, causes concern and is believed to be caused by the immunization. The majority of adverse events following immunization are actually not due to the vaccine itself - many are simply coincidences, others (particularly in non-industrialized countries) are due to human error in the vaccination process. It is important for health care providers as well as potential vaccinees or their parents/guardians to keep in mind that the benefits of protection afforded by a vaccine always far exceed the small risk of a true reaction
Programmes providing immunization services should include a system for AEFI detection and reporting, investigation and management, data analysis, corrective action, relevant communication and evaluation of the system. Most AEFIs reported, particularly in non-industrialized countries, can be linked to improper handling of live vaccines such as measles, BCG or yellow fever vaccines when the vaccine has been contaminated during handling and used beyond the recommended period after reconstitution, or to the reconstitution of the vaccine with an inappropriate diluent, including drugs or other chemical compounds. Programme managers need to be alert to reports of such preventable AEFIs and investigate them urgently in order to take the appropriate corrective action to avoid further cases and minimize the impact of the AEFI on the immunization programme
Vaccine-associated adverse events need to be rapidly and effectively dealt with to avoid undue loss of confidence in a vaccine which can ultimately have dramatic consequences for immunization coverage and disease incidence
RELATED LINKS
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AEFI website
Additional information about managing AEFIs and misconceptions about immunization safety, as well as available resources for surveillance and investigation of AEFIs is provided on the WHO Immunization Safety website -
The Global Advisory Committee on Vaccine Safety
In order to respond promptly, efficiently, and with scientific rigour to vaccine safety issues of global importance, WHO established in 1999 a Global Advisory Committee on Vaccine Safety