The need for more complete information on the background incidence rates of the adverse events was discussed. It was suggested that vital statistics data or other studies of infant mortality be exploited for ecologic correlations, that is to look for changes in mortality in periods before and after new vaccines are introduced. Some participants thought that this was a fairly crude approach to the subject and that it should be looked at in great depth. In addition, one participant thought that there would be too much seasonal and other variation for the infant mortality approach to be helpful unless a concurrent, controlled study were to be done. People must agree to use the same diagnostic criteria for the same conditions.
Much education is necessary to get good background information.
Some felt that this was possible and that having standard definitions then assumes great importance. It was noted that even neurologists have not reached consensus on the definitions of encephalopathy and encephalitis. Previous discussions examined the potential utility of case reports in assessing causality. This is particularly true for assessing the causalities of adverse events that occur shortly after vaccination. Although anaphylaxis, for example, can occur without an obvious cause, the relation to vaccination in an individual case is easy to determine if it occurs within minutes of exposure to the antigen.