Using information from a health insurance claims database, Leckman and his co-authors examined the correlations between specific vaccines and various neurological disorders in six- to 15-year-old children. Children with open wounds and broken bones were used as the two control groups.
While only about 10 percent of children with open wounds had received vaccinations, vaccines had been given to over 20 percent of children later diagnosed with anorexia. Higher numbers of vaccinated children were also found among those who were diagnosed with OCD, anxiety disorder and ADHD as soon as three months after their vaccinations.
Other findings in the study, however, reveal that these correlational results should be taken with a grain of salt.
The broken bone control group also included a higher percentage of vaccinated children, though not as high as that of the anorexia group. Furthermore, vaccinations were more likely to be associated with a lower incidence of major depression and bipolar disorder.
The researchers found correlations for one vaccine in particular: the influenza vaccine, which was associated with higher rates of OCD, anorexia, anxiety disorder and tic disorder.
A biological explanation for these correlations has not been found, but a potential mechanism could lie in the body’s immune response to vaccines, the study suggested.
Vaccines work by prodding the immune system to produce antibodies against viruses and bacteria, thus priming the body against these pathogens before they enter it. Some antibodies, however, can react against not only the intended pathogen proteins, but also against human proteins — a phenomenon called cross-reactivity. A 2015 study published in Science Translational Medicine discovered that antibodies elicited by the Pandemrix influenza vaccine cross-reacted with a human brain protein — hypocretin receptor 2.
Autoimmunity, in which antibodies attack human proteins, is also known to play a critical role in normal brain development, Leckman noted. According to Leckman, if children were experiencing inflammation — a process that promotes autoimmunity — at the time of vaccination, the combination of inflammation and vaccination could have deleterious effects on brain development. Such data on vaccination timing was not included in the database on which the study was based.