Vaccine trials, the most informative way of determining the efficacy of a vaccine, can also provide
valuable information about the burden of disease. The burden of
Haemophilus influenzae
type b (Hib)remains a major barrier to the use of Hib vaccines, especially in Asia. Recent studies in Indonesia and Bangladesh have used vaccine-trial designs, with known effective vaccines, to estimate the vaccinepreventable
burden of Hib disease in those communities. New vaccines against pneumonia and diarrhoeal
diseases are usually directed at only one of various causes of the syndrome. In the case of pneumonia,
it is very difficult to determine the aetiology in most cases, so the vaccine trial offers a means
of determining the burden of vaccine-preventable diseases. This is particularly important for pneumococcal
vaccines as serotype replacement may reduce the effectiveness of the vaccines in the field. This
approach would underestimate disease burden if vaccines were found to have an impact on syndromes
other than those against which they are directed, and might lead to errors in estimation if there were
erroneous assumptions about the efficacy of the vaccine against the condition under investigation.
