BACKGROUND:
Investigators and individuals have suggested that vaccinations may contribute to the development of asthma. Research on this question has been inconsistent and concern about the relationship between vaccines and asthma remains.

OBJECTIVE:
A population suitable for studying the association between vaccinations and asthma will include children with different levels of exposure to vaccinations.

METHOD:
We collaborated with the National Vaccine Information Center (NVIC), an organization that advocates for families who object to mandatory vaccination. The NVIC took measures to ensure the anonymity of their members and reviewed our survey instrument to ensure that data collection was not contrary to their organizational goals.

RESULT:
We mailed 2,966 invitations to participate in the survey and received a response from 1,287 member households. We collected data from 677 eligible families with 1,199 children aged 3-18. The parents were highly educated, predominantly white, and 62% use alternative health care providers. Participants reported many nonconforming health behaviors. By self-report 43% of the children have never received vaccines, 36.5% have received some vaccines, and 20.5% have received all recommended vaccines. Younger children were more likely to be completely unvaccinated.

CONCLUSION:
Research into the relationships between vaccinations and chronic diseases are hampered by small numbers of unvaccinated children in the study population. Atypical health behaviors are common and complicate interpretation of the data. Parents who chose not to vaccinate may also refuse other typical health care and an example of bias level sensitivity analysis to estimate the potential impact of systematic error will be presented.

LEARNING OBJECTIVES:
Families in the anti-vaccine movement are willing to participate in research studies on the adverse effects of vaccines and can be a source of children un-exposed to vaccinations.