Although there are global EPI recommendations that include vaccines against six diseases, each country must decide which vaccines are to be used and which geographic area is to be covered. To provide coverage for the entire target population, the best approach may be a combination of tactics rather than a single one.
WHO recommends that attention first be given to the immunization of children and pregnant women who already use existing health services. Outreach activities may then begin from fixed centers, and finally coverage may be extended throughout the country by taking advantage of the experience gained with fixed units.
In order to decide on appropriate tactics, such as the use of mobile teams or programs based on fixed health services, data on the magnitude of morbidity and mortality from vaccine-preventable diseases may be determined from surveys or health-service records. For example, in many developing countries, data show that measles and whooping cough are important causes of morbidity and mortality, whereas diphtheria is not.
With the data gathered on health problems, quantifiable objectives can be established to reduce disease-specific morbidity and mortality in the target population. The population that WHO recommends for immunization is all children under one year of age and pregnant women, since children in that age group have been observed to be at considerable risk of illness and death from vaccine-preventable diseases.
However, epidemiological information from a given country may show that the selected age should be extended to one and a half or two years, depending on the age at which children contract the disease.
Once the diseases and the selected population have been decided, the next question is how to begin immunizing the target population in the most effective and efficient way. It has been seen that permanent immunization services are less costly and more effective than large-scale campaigns and the use of mobile teams. If static coverage is sufficiently high, campaigns and mobile teams are unnecessary. Otherwise, a mixture of the two tactics may be needed.
Financial, equipment and human resources must also be considered. Mobile teams are costly. Are there sufficient funds and materials to sustain them? Can personnel and fixed health services be used for outreach activities? Are health workers properly trained and motivated? Is there enough equipment to extend the cold chain and immunization throughout the country, or should operations begin in a small geographic area and then be extended as far as possible?
All these questions must be asked and answered before immunization activities are established.
Characteristics of Distribution and Delivery of Each Vaccine
The requirements for stability and refrigeration differ for each vaccine. Tetanus toxoid, DPT and BCG are relatively stable and require refrigeration only at temperatures of +4°C to +8°C. DPT and tetanus toxoid may be stored for more than a year and a half at that temperature, while BCG may be kept for one year. However, DPT and tetanus toxoid must be prevented from freezing.
The poliomyelitis vaccine is less stable than DPT and tetanus toxoid, while the measles vaccine is currently the least thermostable of the EPI vaccines. These two vaccines must be frozen at -20°C when stored for long periods, but for operational reasons they may be kept for up to two years.
All vaccines should not be kept for more than one month at the lowest levels of the cold chain in refrigerators at appropriate temperatures. Research is currently being carried out on vaccine thermostability, so changes in this information may be expected in the near future.
All vaccines used must be approved by WHO and, of course, must not be kept beyond their expiration date.
Cost Analysis in Relation to Benefits, Effectiveness and Efficiency
Cost-benefit studies of immunization programs in developed countries have shown that immunization activities have a high benefit-to-cost ratio. In an analysis carried out for Austria, it was observed that measles vaccination of all children under one year of age provided a cost-benefit ratio of 2.95, higher than that of treatment and care for sick children.
These ratios would be higher in developing countries because both mortality and prevalence of vaccine-preventable diseases are greater there. Although it is almost universally accepted that immunization programs are highly cost-effective when their cost is compared with the cost of treating disease or with the cost of time and productivity lost due to illness and death, the problem remains of keeping immunization expenditures to a minimum.
This is especially relevant for developing countries, where the amount of money available for all health programs is very limited.
