Vaccine safety in immunization programmes

Resurgence of measles outbreak following a decrease in immunization coverage

In the pre-vaccine era, morbidity and mortality caused by infectious diseases that are now preventable were high. Obviously, as vaccines did not exist, there were no adverse events to them yet. The pre-vaccine stage in the graph (STAGE 1) is the phase before the vaccine gets introduced.

In STAGE 2, after an effective vaccine is introduced to prevent a particular disease, an increase in immunization uptake will result in a decrease in disease incidenceIncidenceThe number of new cases (e.g., of a disease, adverse event) occurring in a defined population during a given time interval, often one year., but also adverse events (AEFI), real or perceived, may become a major focus. Paradoxically, it is just when vaccine benefits are most apparent and vaccine coverage is highest that vaccine safety concerns are most likely to increase in the general public.

This increased focus on AEFIs, often intensified by media coverage of one or a few case reports, may lead to:

• a loss of confidence in the vaccine by the public;
• a reduction in vaccine coverage;
• a resurgence of the disease to higher or even epidemicEpidemicThe occurrence of disease within a geographical area and/or population that is in excess of what is normally expected for a given period of time. levels (STAGE 3).

The resurgence of disease or the availability of an alternative vaccine results in renewed public acceptance of vaccination against the disease. Vaccination levels increase and the disease is reduced to earlier low levels (STAGE 4).

For vaccine-preventable diseasesVaccine-preventable diseasesDiseases for which vaccines exist that can confer partial or complete protection. such as smallpoxSmallpoxAn acute, highly infectious, often fatal disease caused by a variola virus and characterized by high fever and aches with subsequent widespread eruption of pimples that blister, produce pus, and form pockmarks. Declared eradicated by the World Health Assembly in 1980. that can be eradicated, vaccine use can be stopped, thereby removing the risk of any adverse eventAdverse event (or adverse experience)Any untoward medical occurrence that may appear during treatment with a pharmaceutical product but which does not necessarily have a causal relationship with the treatment. resulting from its use (STAGE 5). To ensure that the cycle displayed in the graph does not repeat, any vaccine safety issue requires timely detection, evaluation, and response efforts to gain and maintain high public confidence.