Academic journal article Journal of Health Population and Nutrition

Use of Vaccine Trials to Estimate Burden of Disease

Academic journal article Journal of Health Population and Nutrition

Use of Vaccine Trials to Estimate Burden of Disease

Article excerpt

INTRODUCTION

Vaccination has been used for the prevention of specific conditions in different parts of the world for centuries, but the 20th century saw the development of vaccination as a highly effective global public-health strategy (1). The proof that a vaccine is effective has traditionally been provided by a vaccine trial, using epidemiological methods that have been developed over the course of the 20th century. Towards the end of the century, there was a dramatic increase in the price of vaccines, largely because their development and production has been taken over by a small number of large pharmaceutical companies (2). Thus, the later years of the century saw the price of vaccine rise from a few cents to over US$ 50 per dose. This development has meant that even rich countries must now weigh carefully the costs against the benefits of vaccination. The benefits can be seen as having two components--the burden of the disease that is to be prevented and the effectiveness of the vaccine. These two factors together comprise the vaccine-preventable burden of disease.

This paper discusses the growing use of vaccine trials as a method of measuring the burden of disease, the relevance of burden of vaccine-preventable disease as a concept, and the often unrecognized shortcomings of this approach.

In its simplest form, a vaccine trial can be seen as the introduction of a vaccine leading to the reduction or disappearance of the disease against which the vaccine is directed. In the case of an inexpensive and effective vaccine directed against a common disease, such as measles, this may be sufficient to prove the value of the vaccine to public-health officials and to the general public. However, with vaccines that may not be highly efficacious, or diseases that vary in their intensity from year to year, this approach is inclined to yield misleading results. For example, in sub-Saharan Africa and the Middle East, after decades of use against regular epidemics, there are still doubts about the efficacy and duration of protection of meningococcal AC polysaccharide vaccines in young children (3). Another approach is to introduce a vaccine in a manner that leads to only part of the population being vaccinated and then to use epidemiological techniques to compare the likelihood of disease in vaccinated individuals to that in unvaccinated ones. The most commonly-used methods include case-control studies in which the rate of vaccination is compared in diseased versus non-diseased individuals and large-scale modelling techniques in which patterns of disease are related to patterns of vaccine usage (4). The problem with these open approaches is that confounding factors are likely to influence the likelihood of an individual receiving the vaccine, making direct comparisons potentially biased. Such biases are accentuated where the receipt of a vaccine is based on individual choice.

All such methods are inferior to the traditional double-blind, randomized, controlled trial (5). In such a trial, the population under study is effectively divided into compared groups who are equal in every respect, including the likelihood that a case of the disease in question will be detected. In most large trials, this approach avoids the issue of bias, as it can be truly said that the only difference between the groups is whether or not they received the vaccine. Thus, any observed difference in rates of disease, patterns of disease, or mortality can be assumed to be due to the vaccine. If the randomization is undertaken in a 1:1 ratio, it can be assumed that the number of cases in the control group is an indication of the number that would have been found in the vaccinated group in the absence of a vaccine. The number of cases that were prevented by the vaccine can then be calculated, and this presented as a proportion of the total number of cases that would have been expected in the absence of a vaccine. This represents a measure of the efficacy of the vaccine. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.