Objectives of A Vaccine/Immunization Programme

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Chapter: Pharmaceutical Microbiology : Vaccination And Immunization

There is the potential to develop a protective vaccine/ immunization programme for all infectious diseases, although some pathogens are considerably more challenging candidates than others.


OBJECTIVES OF A VACCINE / IMMUNIZATION PROGRAMME

 

There is the potential to develop a protective vaccine/ immunization programme for all infectious diseases, although some pathogens are considerably more challenging candidates than others. Whether or not such vaccines are developed and deployed is related to the severity and economic impact of the disease on the community as well as the effects upon the individual. Various factors governing the likelihood of an immunization programme being adopted are discussed below.

 

1)  Disease Severity

The severity of the disease in terms of its morbidity and mortality, the probability of permanent injury to its survivors and the likelihood of infection must be sufficient to warrant the costly development of a vaccine and its subsequent use. Thus, although influenza vaccines are constantly reviewed and stocks maintained, the control of influenza epidemics through vaccination is not recommended. Rather, those groups of individuals, such as elderly people, who are at special risk from the infection, are protected.

Vaccines to be included within national immunization and vaccination programmes should be chosen to reflect the infection risks within that country. Additional immunizations, appropriate for persons travelling abroad, are intended to protect the at-risk individual, but also to prevent importation of the disease into an unprotected home community.

 

2)  Vaccine Effectivness

Vaccination and immunization programmes seldom confer 100% protection against the target disease. More commonly the degree of protection is 60-95%. In such instances, although individuals receiving treatment have a high probability of becoming immune, virtually all members of a community must be treated in order to reduce the actual proportion of susceptible individuals to below the threshold for epidemic spread of the disease. Anti-diphtheria and anti-tetanus prophylaxes, which utilize toxoids, are among the most efficient immunization programmes, whereas the performance of BCG is highly variable.

 

3)  Safety

No medical or therapeutic procedure comes without some risk to the patient, but all possible steps are taken to ensure safety, quality and efficacy of vaccines and immunological products (see Chapter 24). The risks associated with immunization procedures are constantly reviewed and balanced against the risks associated with contracting the disease. In this respect, the incidence of paralytic poliomyelitis in the USA and UK in the late 1990s was low, with the majority of cases being related to vaccine use (vaccine-associated paralytic polio or VAPP). As the worldwide elimination of poliomyelitis approaches, there is debate as to the value of the live (Sabin) vaccine outside endemic areas, and the inactivated polio vaccine (IPV) is now the vaccine of choice in the UK for prophylaxis against paralytic polio.

 

4)  Public Perceptions

Public confidence in the safety of vaccines and immunization procedures is essential if compliance is to match the needs of the community. The correlation between actual risk and perception of risk is not always reliable, however. In this respect, public concern and anxiety in the mid-1970s over the perceived safety of pertussis vaccine led to a reduction in coverage of the target group from about 80% to 30%. Major epidemics of whooping cough, with over 100 000 notified cases, followed in the late 1970s and early 1980s. By 1992, public confidence had returned and coverage had increased to 92%, with a considerable associated decrease in disease incidence. Similarly, links have been claimed between the incidence of autism in children and the change in the UK from single measles and German measles vaccines to the combined measles, mumps and rubella (MMR) vaccine. Such claims have been proved to be unfounded beyond reasonable doubt but have nevertheless decreased the uptake of the MMR vaccine and thereby increased the likelihood and magnitude of measles epidemics.

 

5)  Cost

Cheap, effective vaccines are an essential component of the global battle against infectious disease. It was estimated that the 1996 costs of the USA childhood vaccination programme, directed against polio, diphtheria, pertussis, tetanus, measles and tuberculosis, was $1 for the vaccines and $14 for the programme costs. The newer vaccines, particularly those that have been genetically engineered, are considerably more expensive, putting the costs beyond the budgets of many developing countries.

 

6)  Longevity Of Immunity

The ideal of any vaccine is to provide lifelong protection of the individual against disease. Immunological memory depends on the survival of cloned populations of B-and T-lymphocytes (memory cells). Although these lymphocytes can persist in the body for many decades, the duration of protection varies from one individual to another and depends on the vaccine; commonly ranging between 10 and 20 years. Thus, if the immune system is not boosted, either by natural exposure to the organism or by re-immunization, protective immunity gained in childhood may be lost by the age of 30. Those vaccines that provide only poor protection against disease may have proportionately reduced timespans of effectiveness. Equally, vaccines may be less effective and have a shorter duration when administered to neonates. Yellow fever vaccination, which is highly effective, must there-fore be repeated at 10-year intervals, while the typhoid vaccine is only effective for up to 3 years. Whether or not immunization in childhood is boosted at adolescence or in adulthood depends on the relative risks associated with the infection as a function of age and the longevity of immunity conferred by the vaccine.


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