With the possible exception of the provision of clean water, no public health intervention has had a more profound effect on reducing sickness and death than vaccination. It is impossible to calculate, and difficult to estimate, the number of lives that have been saved by the routine administration of vaccines. The WHO has provided an estimate of four to five million deaths prevented each year because of vaccines.

Another example of the power of vaccines comes from US data, showing that the number of cases and the number of deaths from the 10 most-feared epidemic and pandemic communicable diseases have been reduced by 96 to 100 per cent.The picture is similar in all Western countries that have similar excellent public health systems.

A GOAL WITH THREE PHASES

The goal of overcoming communicable diseases – for example, through vaccination – can be divided into three progressively ambitious phases: control, elimination and eradication.

Phase 1: Control

At the control stage, diseases have been successfully reduced in frequency to a low level; they are still present in the region or country but do not constitute a significant burden on the healthcare of the population. Control measures do still need to be in place to maintain that low level of disease. These measures include the continuing maintenance of the effective intervention which, in the case of vaccines, means achieving and retaining high levels of vaccine coverage. Importantly, competent monitoring is required to ensure that the disease continues to remain under control. Many vaccine-preventable diseases such as measles, whooping cough and diphtheria would fall into this category in South Africa.

Phase 2: Elimination

The elimination of a disease is defined by the total absence of that disease and the infective agent, in a region or a country, as a result of deliberate, active intervention. Protective measures are essential to ensure that the infective agent is not reintroduced from outside or re-established from any hidden internal source. In addition, to provide confidence and assurance that the infective agent is not present in that region, robust surveillance and monitoring programmes are crucial. Further, vaccination coverage needs to be maintained at a high level to ensure that the population's immunity remains sufficiently protective. In South Africa, polio would fall into this category.