The perceived severity of a disease also affects acceptance of vaccines, as a comparison of two recent disease outbreaks in Canada shows (Pless, unpublished data presented at the workshop). During an outbreak of a particularly deadly type of meningitis, the members of the public readily chose mass immunization to protect themselves from the disease. In contrast, during a measles outbreak, people were less accepting of an immunization campaign because they did not perceive measles as a serious disease. In fact, a child with a case of measles is less likely to die than a child with meningitis, yet because it is so prevalent, measles kills a larger number of children worldwide each year. Before there was a vaccine, measles outbreaks caused many severe complications and deaths, even in developed countries.

Several speakers noted that the perception of control over whether one's children become infected by vaccine-preventable diseases affects the acceptance of vaccine risks. For instance, Maszaros and colleagues found that nonvaccinators believed they could have much more influence in preventing their children from catching whooping cough if their children were not vaccinated than did vaccinators (Meszaros et al., 1996). Nonvaccinators also thought that it was less likely that their child would be disabled or killed by the disease in the absence of vaccination than to suffer the same fate due to receipt of the vaccine. These results suggest a common effect seen in risk communication: that people do not believe expert probability estimates because they think that they have control in ways that experts may not have anticipated. In the Washington, D.C., survey mentioned previously, responses to the question of why parents did not vaccinate their children included a belief in self-healing and folk remedies (McLaren, unpublished data presented at the workshop).

Ethical and Policy Issues

Acceptance of the risks associated with vaccination depends, in part, on the weight that a person gives to societal good versus individual rights. Although childhood vaccines may prevent much death and disability from disease while causing relatively few deaths or disabilities from adverse effects, some participants felt that it is not appropriate to compare the value of lives lost due to adverse reactions to a vaccine to the value of lives lost due to the natural disease. A consumer advocate stated that Americans should never be forced by the government to engage in any medical procedure which carries the risk of injury or death, including vaccination, without informed consent. Citizens should have the right to be fully informed about the benefits and risk of vaccines and make independent decisions about which risks to take, including the right to select the preventive health care that is appropriate for their families, she said.

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