Other research shows that people tend to have a preference for eliminating risk and for maintaining the status quo (Thaler, 1980; Samuelson and Zeckhauser, 1988). Consequently, people often have an aversion to increasing the probability of one type of risk to reduce that of another, even by the same amount. They may even prefer a riskier situation over a less risky situation if the former maintains the status quo (Fischhoff et al., 1981).
Influences on and Biases of Experts
Experts in a particular area may (or may not) be less likely to exhibit, in their own field of expertise, the specific heuristic rules and biases discussed above. Experts also have their own biases. Their values, beliefs, and attitudes influence the form and content of the risk and benefit information that they present. In addition, organizational biases (such as whether experts are affiliated with a government agency promoting vaccination, a vaccine manufacturer, or a consumer organization concerned with vaccine safety) can also influence how experts view an issue.
Because of their particular professional training, their mental models and approaches to problem solving can differ fundamentally from those of nonexperts (Chi et al., 1981). For example, in their search to draw conclusions or solve problems, they may sometimes rely inappropriately on limited data, impose order on random events, fit ambiguous evidence into their own predispositions, omit components of risk such as human errors, and be overconfident in the reliability of analyses (Fischhoff et al., 1982; Fischhoff and Merz, 1995; Freudenberg and Pastor, 1992).
Influences on the Acceptability of Vaccine Risks3
Individual's immunization decisions are influenced by decisions that others make. Recent studies illustrate specific factors influencing how vaccine risks and benefits are perceived by and acted on by consumers and vaccine providers. People might prefer to do what a majority of others do (bandwagoning) or may take advantage of the protection afforded by high immunization rates and not be
vaccinated (free-riding); they may also be influenced to vaccinate by the fact that vaccination would protect others (altruism). Other factors include perceptions of disease risk and the ability to control those risks, and preferences for the risks of diseases per se over risks of the vaccine against them. Studies have also addressed issues of mandatory vaccination, informed consent, individual rights versus societal welfare, and people's trust in information providers.
The Logic of Vaccination Decisions: Bandwagoning, Free-Riding, and Altruism
A major influence on the acceptance of vaccine risks is whether people employ what is known in the risk communication field as bandwagoning, free-riding, or altruistic logic. Bandwagoning refers to the tendency for individuals to choose the decision of the majority as an indication of what might be a wise action for themselves, without fully evaluating their options. A study at the University of Pennsylvania found, for example, that when parents who vaccinate their children were given a hypothetical situation in which 100 percent of other children were vaccinated for a particular disease, 95 percent said that they would also vaccinate even though their children would be at no risk of catching the disease (Meszaros et al., 1996).
The tendency to bandwagon is countered by free-riding logic. People who follow this logic feel that they do not have to expose themselves to the risks of vaccination because they are protected from disease by the vaccination of the majority of other people (a phenomenon known as herd immunity). Nonvaccinators in the University of Pennsylvania study were more likely to use free-riding logic than were vaccinators. People who use altruistic logic, in contrast, are willing to take on personal risks if a large number of people will benefit by their doing so. Overall, bandwagoning appears to be much more common than either altruism or free-riding (Hershey et al., 1994).
Perception of Disease Risks
Perception of the risk of contracting a disease influences willingness to accept the risk of a vaccination. For example, a common misconception among parents in one Washington, D.C. survey is that vaccine-preventable diseases have been virtually eliminated in the United States, thus ending the need to immunize children (McLaren, unpublished data presented at the workshop). The success of vaccination programs in reducing the incidence of vaccine-preventable diseases in the United States makes it more difficult to communicate the risk of those diseases.
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.
In contrast, others believe that governments have the right and responsibility to override individual autonomy if there is a compelling public health interest. An epidemiologist commented that the logic of public health laws, requiring quarantine for instance, suggest that although an individual might choose not to be vaccinated and to take the risk of being infected by a communicable disease, he or she does not have the right to make that choice if it promotes the infection of other individuals. Some groups claiming religious and philosophical objections to vaccination respond to this by voluntary quarantine, for the sake of their own children as well as others. Walsh, a political philosopher, concluded that ''compulsory childhood vaccination is not on strong philosophical grounds.'' It can be ethical, Walsh says, to require public health measures such as quarantine and mandatory vaccination, but only when the survival of the community itself is at stake. It is debatable whether the communicable diseases for which there are vaccines actually threaten community survival, he said.
Mandatory vaccination laws require children to receive several specific vaccines before being allowed to enter public school (and, in some cases, day care as well). Every state makes provision for exemptions to mandatory vaccination on medical grounds; all but three states allow exemptions on religious grounds; but only 16 states allow exemptions on philosophical grounds (CDC, 1995). Several speakers were highly critical of mandatory vaccination policies and, particularly, the lack of exemptions on philosophical grounds in many states.
Some participants stressed that a lack of exemptions for mandatory vaccination on philosophical grounds can seriously impair risk communication about vaccines. Mandatory vaccination influences not only how vaccine risks and benefits are received by the public but also the content and form of risk communication about vaccines. A practicing physician and academician noted that if vaccination were not required by law, there would be a need for better communication about the risks and benefits of vaccines.
Participants discussed the effect on vaccine coverage of allowing greater access to exemptions on philosophical grounds within a mandatory vaccination program, with several speakers commenting that the overall effect might be relatively small. For example, speakers who promote immunization for public health departments and private organizations commented that few parents whose children are unvaccinated cite philosophical reasons for the lack of vaccination. Instead, most have inadequate access to health care, are unaware of recommendations for early childhood vaccination, or have not made vaccination a priority. In some cases, their physicians may not have suggested immunization when the child sought treatment for other reasons. Mandatory vaccination policies require such parents to consider vaccination and make a decision, said a participant who formerly administered the immunization program for the city of Philadelphia. He described that city's experience after making measles vaccination mandatory
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).
Uncertainty and Trust
The degree of trust that recipients place in the communicators of information about vaccine risks and benefits, as well as the ability of the communicators to convey any existing uncertainty about adverse events, also influences decisions made about vaccination. For example, the University of Pennsylvania study found that nonvaccinators exhibited significantly more skepticism about medical information in general and about vaccines and their effectiveness in particular (Meszaros et al., 1996).
A lawyer stated that there is a fundamental conflict of interest in vaccine risk communication because health officials and health care providers, in the interest of public health, generally see their roles as encouraging immunization. Their natural tendency, consequently, will be to emphasize the benefits of immunization and in their communications minimize the risks about vaccines. At the same time, they have the responsibility to provide their patients accurate and unbiased information on the nature and extent of the risks involved with vaccination. Ultimately, the public might be better served if public health officials, health care providers, and the population they serve all worked towards the development of a trusting relationship, in which public health officials were seen as having responsibility for ensuring the health of the population, including balancing disease and vaccine risks (IOM, 1996b).
A consumer advocate said that vaccine manufacturers, providers, and policymakers knew that there were risks associated with vaccine use when vaccines were first marketed but did not adequately communicate those risks to the public. Nor was it communicated that there was some uncertainty and disagreement about what was known, she said. "This failure to communicate what medical science does and does not know about vaccine risks was quite simply perceived as a fundamental betrayal of trust by those who were being asked to take the risks," she said. When government and industry's media campaigns to achieve a high vaccination rate downplayed vaccine risks, there was further erosion of trust. Overzealous enforcement of mandatory vaccination laws, she said, also fosters a lack of trust.
A vaccine manufacturer's representative noted that part of the problem with trying to convey risks following vaccinations to the general public is that frequently the true risks are not known. There are a range of views as to which adverse events should be discussed in written statements and other communications about vaccines. The position at one end of the continuum is to describe only those risks that are shown by conventional scientific standards to be causally associated with the vaccine. The position at the other end is to claim safety only with regard to adverse events that can be shown not to be associated with the vaccine and then to describe equally all other putative adverse events. The