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OCR for page 206
Page 206
Afterword on Research Needs
In the course of its review, the committee found many gaps and
limitations in knowledge bearing directly and indirectly on the
safety of vaccines. Such shortcomings relate, for example, to
pathologic mechanisms of specific infectious agents, the molecular
basis of vaccine injury, and the natural history of conditions such
as encephalopathy, mental retardation, and chronic arthritis. Many
of the reports of case series suffer from inadequate or
inconsistent case definitions, variable details about cases,
inclusion of nonrepresentative case groups, and failure to consider
potential confounding variables or biases. In addition, existing
surveillance systems of vaccine injury have limited capacity to
provide persuasive evidence of causation. Many of the
population-based epidemiologic studies are too small or have
inadequate lengths of follow-up to have a reasonable chance of
detecting true adverse effects, unless these effects are large or
occur promptly and consistently after vaccination. If research
capacity and accomplishment in this field are not improved, future
reviews of vaccine safety will be similarly handicapped.
The committee found few experimental studies published in
relation to the number of epidemiologic studies published. As noted
in Chapter 2, withholding of vaccines can be regarded as unethical.
Although the committee was not charged with, and has not attempted,
full consideration of the kinds of studies that would be both
ethical and especially informative, either in the areas of vaccines
that it has been charged to study or more
OCR for page 207
Page 207
generally, it recognizes, nevertheless, that opportunities may
exist for informative experiments in human populations that take
advantage of the possibility of using alternative schedules for
administration of vaccines.
A careful review is needed to identify what sorts of questions
might be best answered by further investigations and which kinds of
studies could be carried out economically. The availability and
introduction of new forms of pertussis vaccine, for example, could
offer valuable opportunities for comparison of vaccine safety as
well as efficacy. The committee is not in a position to make
specific recommendations, but its experience points to fresh
possibilities and to the need for such a review.
Representative terms from entire chapter:
studies published