7.3 Organisational difficulties
As the Polio Case Study illustrated, the attempt to eradicate a major infectious disease requires an immense effort to organise systematic vaccination programmes throughout all endemic regions, backed up by vigilance to identify residual areas where the pathogen may be persisting or could have been re-introduced. Mass vaccination programmes present a huge logistical task for those who are engaged in their organisation and delivery. Consider what must be involved in administering the National Immunisation Days (NIDs), which aim to vaccinate several million children concurrently at hundreds of centres throughout countries such as India, Somalia or Peru.
Suggest some of the challenges such an event poses for its organisers.
The inaccessibility of many parts of the country is a major problem, both for getting the vaccination clinics set up in mountainous regions, deserts, tropical rainforests, etc., and for the population who must make long and difficult journeys to attend them. Advertising an NID and explaining its purpose and importance is not straightforward in remote populations with high levels of illiteracy and many spoken languages. Staff must be trained to administer the vaccine correctly and safely; transport and storage facilities for supplies must be organised to ensure adequate population coverage. House-to-house follow-up has to be made to ensure that vaccinations are repeated to ‘boost’ immunity to protective levels.
Organisational problems such as these mean that the conduct of mass vaccination programmes is often less than ideal, particularly but not exclusively in developing countries. For example, the WHO's Immunization Safety Project ( reported in 1998 that up to one third of vaccinations were not being carried out in a way that guaranteed sterility, and only one third of countries importing vaccines had a monitoring system to detect vaccine-associated adverse events. The procedures for ensuring optimum storage of vaccines and disposal of injection equipment were often inadequate, and the most up-to-date vaccines could not always be afforded or obtained.
What ‘perverse effect’ of vaccination could occur in a community where a poorly organised vaccination programme failed to achieve population coverage at or above the critical immunisation threshold?
The average age at infection of the unimmunised individuals in the population increases, because their contact rate with sources of infection is reduced by the pool of vaccinated people all around them. If the infection is one that causes more severe symptoms or permanent damage in older individuals (e.g. polio, mumps, hepatitis A virus), then a ‘sub-threshold’ vaccination programme will result in an increase in the proportion of adverse outcomes in those who develop the disease at a later age.
Perverse effects such as these have contributed to public anxiety about the safety of vaccination programmes.