Researchers are currently conducting studies aimed at assessing which populations are at risk for certain adverse events, including determining the allergies that make people prone to anaphylactic reactions following vaccination against measles, mumps, and rubella, identifying the neurologic impairments that may make infants more prone to convulsions following vaccination with DPT, assessing premature infants' responses to vaccines, and determining the underlying cause for the increased mortality observed in some populations of girls given high-titer measles vaccine.
A number of questions remain unanswered regarding risks for adverse events following vaccination and ways to lower such risks. Several speakers suggested research avenues that might prove fruitful in this regard, including studies that assess the risk of adverse events after vaccination in specific genetic populations; on a molecular biology level, the impact over time of multiple vaccinations; whether there is a link between learning disabilities and vaccination; whether autistic children have different immune responses than nonautistic children; whether health care workers vaccinated with the hepatitis B virus vaccine (HBV) experience more autoimmune disorders; and whether the antigens in vaccines are likely to cause demyelinating disorders. Although several forum members and other workshop participants voiced concern that some of these studies would be difficult to design or impractical to conduct, the information that they would provide, if the studies are successfully carried out, might be valuable in determining risks for adverse events following vaccination.
As discussed at the workshop, a number of immunologic and genetic variables are likely to foster diverse responses to vaccines. Because vaccines work through their effects on the human immune system, some scientists who study vaccine adverse effects have concentrated on allergic reactions or autoimmune processes as potential causes of adverse effects. Reflecting these ideas, the first session of the workshop addressed research on immune responses to vaccine antigens. If adverse reactions to vaccines are autoimmune reactions, as discussed in the previous section, then susceptibility to adverse events after vaccination might depend in part on an inherited or genetic susceptibility to such reactions. If so, the study of such disorders might provide insight into genetic susceptibility and expression. Reflecting these issues, the second session of the workshop addressed genetic variability in immune factors, and the interaction of these factors with environmental agents.
Certain populations may be more susceptible to adverse events following vaccination because of some of these variables. The third section of the report