REQUIREMENTS OF AN IDEAL VACCINE FOR TODAY

October 3, 2008 by dadmin

Before discussing the way in which the immune system functions and how vaccines can work, it might be a useful exercise for the student to consider what an ideal vaccine should consist of. For example, most vaccines today are administered parenterally and this can sometimes be a painful or distressing experience, especially for young children. At the 1990 International Task Force for Vaccine Development meeting in New York, a children’s vaccine initiative (CVI) was set up with the aim of developing an ideal vaccine. The following criteria were established although the list may not be totally inclusive.

1. A vaccine should only require a single dose.

2. A vaccine should be given early in life.

3. The route of administration should be nonparenteral.

4. Vaccines should be combined in order to reduce the number of visits to a doctor or medical center.

5. Vaccines should be heat stable and retain activity during transport and storage, especially in tropical climates.

6.Vaccines need to be developed against diseases with high mortality rates, such as AIDS, pneumonic plague, acute respiratory infections, diarrhea, and parasitic diseases such as malaria.

7. And, above all, the cost must be low throughout the world. The ultimate vaccines in the future will be required to fit these criteria and it is not difficult to see that the cost may be the biggest problem.

In the 15 years since these criteria were promulgated by declaration, it will be evident that most vaccines are still administered parenterally with the exception of polio and typhoid vaccines. In many ways this can be attributed to the physicochemical characteristics of vaccine antigens themselves, which are large molecules susceptible to proteolytic degradation, denaturation, and rapid clearance from plasma. Some combination vaccines are available which reduce the number of injections. However, the MMR (measles, mumps, and rubella) combination vaccine has gained an unsafe image in the popular press, mainly due to a reputed link with autism in some children that as yet remains unproven scientifically. In some quarters the autism was associated with the use of thiomersalate as a mercurial preservative in multidose injections but, again, this supposition remains unproven. The controversy has reappeared with the introduction of a five component children’s vaccine containing diphtheria, polio, measles, mumps, and rubella; although this should be much more convenient and contains a killed polio instead of an attenuated virus which is known to occasionally revert to the active form, albeit in single numbers per million injections. In this case the children’s vaccine should be safer and more convenient.

Throughout this chapter the reader should bear in mind the possibility that modern biotechnology, the subject of the book as a whole, is making progress toward the ideal criteria outlined above.

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