Some of you might remember the previous post here titled “Thanks, Andrew Wakefield,” talking about the anti-vaccine movement and its negative consequences on infectious disease rates. Lately, according to Orac over at ScienceBlogs, anti-vaccine activists have been demanding a study of vaccinated versus unvaccinated children. As pointed out, a randomized, double-blind study of vaccinated vs. unvaccinated children would be highly unethical given that vaccines are already proven to reduce disease among the vaccinated.
In response, some anti-vaccine activists have taken to demanding an observational study rather than an experimental one – a study where the differing rates of infection in vaccinated vs. unvaccinated children are merely observed, rather than controlling who is vaccinated or not. Never mind that there are a large number of confounding factors that would make it difficult to conduct such a study (subjects would have to be matched for age, sex, socioeconomic group, geographic location, urban vs. rural vs. suburban setting, race), and that there are only approximately 50,000 unvaccinated children ages 3-6 in the U.S.; this observational study is apparently the way to go.
“Fine,” said a study just reported in Deutsches Ärzteblatt International. Roma Schmitz and colleagues from the Robert Koch Institute reviewed results from the German Health Interview and Examination Survey for Children and Adolescents, double-checking the responses against medical records for accuracy. Schmitz and her co-authors compare the occurrence of infections and allergies in vaccinated vs. unvaccinated German children and adolescents – exactly the kind of observational study requested by anti-vaccine activists. The authors even specifically state that they did the study because of the anti-vaccine movement.
The findings shouldn’t be surprising – the only difference between the vaccinated vs. unvaccinated children was in the incidence of vaccine-preventable infectious disease. In other words, vaccines work, and if your child isn’t vaccinated, they are more likely to get the disease that the vaccine would have prevented.
However, the controls that the authors used in the study are extremely interesting; they looked at incidence of infectious disease in general between the two groups, as well as incidence of allergies and immune dysfunction. They found that unvaccinated children were just as likely to have other infectious diseases, were just as likely to have allergies, and were just as likely to have immune system dysfunction as the vaccinated children. I.e., vaccinated children aren’t at any higher risk of developing some of the negative consequences that anti-vaccine activists are so worried about.
The study doesn’t measure prevalence of autism, because, as explained by Orac, “there were only 94 unvaccinated children, which makes it impossible to compare autism and ASD [Autism Spectrum Disorders] prevalence with the vaccinated cohort, because the expected prevalence of autism is only approximately 1 in 100 anyway, which means that on average less than one autistic child would be expected in such a cohort. To look at differences in autism prevalence between the groups, many times more than 13,000 subjects would be needed.”
So, the study shows that vaccines work, and don’t cause any harm (as measured in the study). Ironically, the study was just what anti-vaccine activists said they wanted, though they most likely won’t like the results.
Deutsches Ärzteblatt International paper: http://www.aerzteblatt.de/int/article.asp?id=80869
Orac’s post on ScienceBlogs, a good discussion of the paper: http://scienceblogs.com/insolence/2011/03/for_the_anti-vaccinationists_out_there_t.php