This is the finding of a Northwestern University study reported in today's issue of the Journal of the American Medical Association (JAMA).

Robert M. Wolfe, M.D., and colleagues from Northwestern's Feinberg School of Medicine examined the content and design of antivaccination websites to look at the specific claims and concerns expressed by the antivaccination groups.

"Vaccines are considered one of the greatest achievements of biomedical science and public health," the authors write. "However, during the last few decades an increasingly vocal antivaccination movement has challenged the safety and effectiveness of the recommended vaccines."

The researchers cite a recent national survey that found the majority of parents supporting vaccination -- although "25 percent believed that vaccinations could weaken children's immune systems and 23 percent believed that children get too many immunizations."

Using a metasearch program incorporating ten Internet search engines, the researchers reviewed and analyzed 772 links to find 12 websites that provided antivaccination information. The researchers were able to find another 10 antivaccination sites from the original 12 through Internet links, resulting in a total of 22 sites for the study.

The researchers then used a standardized form to systematically evaluate the sites for specific content and design attributes.

"Our results show that such sites express a variety of claims that are largely unsupported by peer-reviewed scientific literature," the authors report. "The most commonly found content claims were that vaccines cause idiopathic [unknown cause] illness (100 percent of sites), vaccines erode immunity (95 percent), adverse vaccine reactions are underreported (95 percent), and vaccination policy is motivated by profit (91 percent)," the researchers report.

The authors note that these sites also provide links to other antivaccination sites and provide information on how to legally avoid immunizations.

"Fifty-five percent of the sites provided personal accounts written by parents who believed that their child was killed or permanently harmed by vaccination, and almost one fourth of the sites included pictures of the affected children," the authors state.

Those images can be unsettling to parents who may be swayed by the personal stories rather than by any scientific evidence, the authors suggest. The researchers also found that 64 percent of the sites had information on how to legally avoid immunizations.

"Vaccination is not risk free, but most in mainstream medicine agree that the benefits of vaccination outweigh the risks," the researchers comment. "Although a few unimmunized individuals are most likely protected by herd immunity, growing numbers of unvaccinated individuals could eventually pose a risk to both themselves and society. We believe our study findings can help direct research aimed at more effectively addressing the concerns of individuals opposing childhood vaccination," the authors conclude.

According to background information in the article, recent studies have indicated that 66 percent of U.S. adults (137 million) are now online and that 80 percent of all adults online use the Internet to look for health information. Furthermore, 52 percent of those who have visited online health sites believe that "almost all" or "most" of the health information they find online is credible.

(Reference: JAMA. 2002; 287:3245 - 3248. Available at this URL.)

Related websites:

The Allied Vaccine Group (A vaccination information website)

Think Twice Global Vaccine Institute (An antivaccination website)

26-Jun-2002