for public school attendance. Immunization levels for measles rose from between 80 and 85 percent to more than 95 percent, even though exemptions to vaccination on philosophical grounds were permitted. An epidemiologist, noting that a vaccination program can be effective even when immunization rates are less than 100 percent (Fine and Clarkson, 1986), a phenomenon known as herd immunity, suggested that even if a slight decrease in coverage occurred efforts in the United States would not necessarily be seriously hampered. Another epidemiologist noted that immunization rates in the United States, unlike other countries, did not fall in response to increased media attention to the safety of pertussis vaccine in the 1970s and 1980s, and that this might not have been the case if philosophical exemptions had been widely available.

A number of speakers questioned whether mandatory vaccination is consonant with a patient's right to informed consent. Informed consent is a legal and ethical doctrine adopted by the medical profession and courts in the 1950s. It is defined as occurring when information about the risks and benefits of a medical procedure "is disclosed by a physician to a competent person, and that person understands the information and voluntarily makes a decision to accept or refuse the recommended medical procedure" (Meisel et at., 1977). As some participants noted, consent is truly "informed" when an individual knows the risks and benefits and makes a voluntary decision.

An ethicist noted that informed consent can radically change the meaning of a transaction. As an extreme example, he said, the primary difference between assault with a deadly weapon and surgery or between servitude and employment may well be informed consent. Informed consent not only offers an avenue for communicating the risks and benefits of vaccination but also can influence how readily people accept the risks associated with vaccination. A media representative commented that people who are exposed to risk information take more responsibility for health care decisions and thus are less likely to blame others when the unexpected happens.

Informed consent with the aim of promoting a decision that someone believes is best for the individual can backfire in the vaccine arena, noted one speaker, an expert on risk communication. "The choice not to immunize may be optimal to the individual if there is herd immunity," she said, "but in the aggregate, this choice could lead to failure of that herd immunity." In addition, immunization can be beneficial to individuals other than those vaccinated (if, for instance, the disease could be more severe for the others) even without herd immunity. This perspective suggests that informed consent for individuals may not always lead to the greatest good for the community but sometimes can contribute to a "tragedy of the commons,'' in which the common good (herd immunity, in this instance) is affected if too many people make the decision not to immunize (Hardin, 1968).

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