Gordon Ada, Division of Cell Biology, John Curtin School of Medical Research, The Australian National University, Canberra, Australia
Vaccines developed from the need to prevent the continuing morbidity and mortality from infectious diseases. The earlier attempts included variolation, the practice of deliberately inducing disease by transmission of material from smallpox pus or scabs which was practised in China and India and spread to the Middle East and thence to Europe and America. Despite the high risk of variolation (0.2-2% mortality), it was much less than the risk of death from being infected during a smallpox epidemic. Benjamin Franklin stated in his autobiography, 'In 1736, I lost one of my sons (Francis Folger), a fine boy of four years old by the smallpox. I long regretted bitterly and still regret that I had not given it to him by inoculation. This I mention for the sake of parents, who omit the operation on the supposition that they should never forgive themselves if a child died under it; my example shows the regret may be the same either way, and that therefore the safer should be chosen.'
The history of vaccination has many dark episodes and it has been vigorously opposed by different groups during the 200 years since Edward Jenner showed the value of 'vaccinating' with material from cowpox in protecting from a subsequent attack of smallpox. The value of vaccination has always been a balance between benefit and risk.
For livestock, the benefit outweighs the risk; for medical use, safety has increasingly become the major consideration. Rigorous criteria for the assessment of a candidate vaccine's safety and efficacy now exist, particularly in a number of industrialized countries. Prior to human use, regulatory authorities, such as the Food and Drug Administration (FDA) in the USA, require extensive animal tests for toxicity and sometimes for teratogenicity, and trials for efficacy in lower primates. The primate may or may not be an entirely relevant model for the human disease. For example, neither the chimpanzee for human immunodeficiency virus (HIV) nor different monkeys for Plasmodia reproduce the human disease symptoms, but at least the animals sustain an infection.
Clinical trials in humans occur in three or four stages which may vary according to the preparation. In a phase 1 trial, the candidate vaccine is administered to human volunteers to test mainly for safety but also where practical for an indication of immunogenicity. If a vaccine is produced in an industrialized country, it is usual for the trial to be carried out in that country, even though the vaccine may be destined for use in a developing country. Phase 2 trials are conducted to test further safety and immunogenicity, but in addition, an indication of the efficacy of the product in those who may be exposed to the infectious agent. Phase 3 trials are carried out in the field on a much larger number of participants, perhaps up to 100 000 depending on the prevalence of the disease in the population. Phase 3 trials in particular may be very expensive, sometimes running into millions of dollars. Finally the vaccine is licensed or registered for use but where possible, a large number or a cohort of vaccinees should be followed in a postregistration program.
A candidate vaccine may run into difficulties at any of these stages or after registration, depending on the frequency of occurrence of the side-effects. Several examples are now quoted which illustrate past or present experiences.
Was this article helpful?
All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.