January 2000
BALTIMORE - Religious and philosophical convictions may hold severe consequences when it comes to the transmission of vaccine-preventable diseases in children. A recent study of school-aged children and adolescents ages 5 to 19 found those with exemptions 35 times more likely to contract measles than people who are vaccinated. Relative risk varied by age, year and geographic location.
According to Daniel A. Salmon, a PhD candidate, Johns Hopkins University, fewer than 1% of U.S. children are not vaccinated due to religious and philosophical exemptions. However, those who are exempt from vaccination may pose a risk to the community, because unvaccinated or under-vaccinated people are at an increased risk of contracting vaccine-preventable diseases and are a source of disease transmission. In 1992, children age 5-19 were 10 times more likely to contract measles than people who were vaccinated. In 1988, the risk of contracting measles for unvaccinated children age 5-9 was 170 times the risk of vaccinated children.
Every state requires proof of immunization for school entry. Paradoxically, states allow exemptions for medical reasons (all 50 states), religious reasons (48 states) and philosophical or personal reasons (15 states). Exemptions are defined by each individual state and may require a letter from a physician, a parental affidavit or written acknowledgment from a faith leader claiming the member of a recognized religious group opposes all immunizations.
More than 98% of school-age children today are vaccinated, and while vaccines cause fewer complications than actually acquiring a vaccine-preventable disease, no vaccine is entirely safe. "Vaccines, overall exceptionally safe and exceptionally effective, are not 100% safe or 100% effective," Salmon said. "So it is easy for public attention to shift from the diseases to the vaccine. If you look at it from a public perspective, when a disease is prevalent and feared, people focus on it. When a disease has been controlled for a long time because of the widespread and sustained use of vaccines, people don't have a proper sense of fear, because it's out of sight and out of mind."
The number of exemptions reflects the divergence in perceived risk-benefit of vaccination. For instance, in the United States, where levels of reported vaccine-preventable diseases are low and adverse events following immunization are highly publicized, the debate over appropriateness of exemptions and mandatory immunizations is likely to continue.
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According to the study, there have been reports of vaccine-preventable outbreaks that started in vaccine-exempt individuals. For instance, a 1996 measles outbreak in Utah resulted in 118 cases, with 107 isolated to Washington County. Data from the Utah Immunization Program indicates Utah has almost three times the national average (1.2 %) of measles cases, with Washington County having more than seven times the national average (3.7%). Of those infected in the Washington County outbreak, 45% were exempt from vaccination because of their beliefs.
The large percentage of people with exemptions infected in the 1996 outbreak suggests they played a major role in the transmission of the vaccine-preventable diseases. It also illustrates the clustering phenomenon where a large number of exemptions occur in a given social sphere, such as a school, social organization or religious community.
"There is a balance between individual rights and public good," said Salmon, "with a distinction between individual risk and community risk. There are two sides to it. If I choose not to vaccinate my child, what risk am I putting my child at? If my child is not vaccinated and your child is in a classroom with my child, the choice I made for my child puts your child at risk. I think it's important for parents trying to decide whether or not to vaccinate to realize that the risk that comes along with that decision isn't just a risk to their children, but a risk to others."
The measles vaccine is estimated to be about 90% to 95% efficacious. When a high enough percentage of the population is immunized, unvaccinated people experience indirect protection from disease when enough surrounding people are immunized (herd immunity).
"The parent wishing to minimize individual risk may decide to avoid vaccination by claiming an exemption, relying on the fact that others are vaccinated to provide protection. Everybody else is taking the very, very small risk associated with vaccines and I'm not. Yet, I benefit because everybody else is vaccinated," said Salmon.
However, the greater the number of exemptions, the greater the effect on the immunized public. Study data show if the number of exemptions doubled, the incidence of measles in the non-exempt population would increase by 5.5%, 18.6% and 30.8% for mixed groups with exemptor populations of 20%, 40% and 60%, respectively. If a large enough number of individuals are exempt from vaccination, a resurgence of vaccine-preventable diseases could occur.
"The movement to encourage people not to immunize is certainly gaining momentum," said Eugene J. Gangarosa, MD, professor emeritus, Emory University. "Exactly what the overall impact will be remains to be seen. Our concern arises from what happened in other countries; for example, in Sweden, the United Kingdom, Japan and the newly independent states of the former Soviet Union where similar movements resulted in disruptions of vaccination programs and epidemics of vaccine-preventable diseases."
Gangarosa noted that both the medical profession and anti-vaccination groups are concerned with making sure parents are well informed about vaccination issues. "But what we are concerned about is that some health jurisdictions give vaccination exemptions without knowing whether or not the parents are well informed.
"We're exploring the development of a policy that would say to parents: `If you feel strongly about this, do you understand the implications?' We are suggesting it would be appropriate to ask parents certain questions, not as a punitive measure, but to make sure they are adequately informed and advised as to what the risks are to their children as well as others."
| Relative Risk for Measles Among Individuals with Religious and/or Philosophical Exemptions, 1992* | |||||||
|---|---|---|---|---|---|---|---|
| Age Groups | No. of Exemptor Cases | Exemptor Population | Exemptor Incidence per 100,000 | No. of Vaccination Cases | Vaccinated Population | Vaccinated Incidence per 100,000 | Relative Risk (95% Confidence Interval) |
| 5-9 | 9 | 84,784 | 10.62 | 145 | 17,896,080 | 0.81 | 13 (7-27) |
| 10-14 | 9 | 83,421 | 10.79 | 99 | 17,682,344 | 0.56 | 19 (10-39) |
| 15-19 | 4 | 77,682 | 5.15 | 214 | 16,798,768 | 1.27 | 4 (2-12) |
| 5-19 | 22 | 245,887 | 8.95 | 458 | 52,377,192 | 0.87 | 10 (7-16) |
| *Exemptors indicate people who have
religious and/or philosophical exemptions from mandatory school immunization
laws. Source: JAMA. 1999;282:47-53. |
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For more information:
- Salmon D, Haber M, Gangarosa E, et al. Health consequences of religious and philosophical exemptions from immunization laws: Individual and societal risk of measles. JAMA. 1999;282:47-53.
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