Another set of hypotheses proposes that vaccines cause autoimmune diseases such as multiple sclerosis or type 1 diabetes by inadvertently stimulating the immune system to attack itself. The mechanism of "molecular mimicry" is based on the fact that some proteins on invading microbes are similar to human proteins. In responding to proteins from the infectious agent, the immune system may mistakenly attack similar proteins in the patient's body, and set off a disease.
Molecular mimicry may indeed allow a natural infection to trigger an autoimmune disease, as when Lyme disease leads to chronic arthritis. However, says Dr. Offit, this process cannot be extended to what happens with vaccines. Naturally occurring viruses and bacteria are much better adapted to growing in humans than vaccines, and are much more likely to stimulate potentially damaging autoimmune reactions.
"Vaccines are engineered to carry weakened or deactivated pathogens, and consequently there are critical differences between natural infection and immunization," said Dr. Offit. "These differences are reflected in the many well-controlled epidemiological studies that do not show a causal relationship between vaccines and autoimmune diseases, including multiple sclerosis, type 1 diabetes and chronic arthritis."
'"/>
Contact: Erin McDermott
McDermotte@email.chop.edu
215-590-7429
Children's Hospital of Philadelphia
3-Mar-2003