By the Blouin News Science & Health staff

Autism diagnoses not related to number of vaccines

by in Fitness & Wellbeing, Medicine, Research.

A group of disabled people in wheelchairs join a parade for World Autism Awareness Day in Manila, Philippines on April 2, 2013.

(REUTERS/Romeo Ranoco)

There is no connection between autism spectrum disorders and the number of vaccines children receive before age two, confirms a study published last week in the Journal of Pediatrics.

Over 12 years after the Lancet formally retracted Andrew Wakefield’s discredited paper linking autism to the MMR vaccine, its legacy still looms — a recent survey found that more than 10 percent of parents delay or refuse vaccination for their children. Public health advocates are often frustrated by the persistence of the belief that vaccines cause autism in spite of the mounting evidence against it. They hope that the current study, led by Frank DeStefano of the Centers for Disease Control and Prevention, will reassure parents about the safety of immunization and encourage them to vaccinate their children.

The agents in vaccines that stimulate the body’s production of disease-fighting antibodies are called antigens. To assess the risk of developing autism after being vaccinated, researchers compared the number of antigens injected in children with and without autism spectrum disorders (ASDs). The researchers based their analysis on the vaccination histories of 256 children with ASDs and 752 children without ASDs born between 1994 and 1999. In addition to calculating the total number of antigens each child was exposed to before age two, the researchers examined the maximum number of antigens the child absorbed in a single day.

According to the study, the number of antigens and intensity of antigen exposure was the same for children with and without ASDs, indicating that the vaccine schedule did not contribute to the development of autism. The results corroborated a 2004 review by the Institute of Medicine, which rejected the hypothesis that the MMR vaccine caused autism. A more recent study published in 2013 also confirmed the safety of the 24 vaccines children are supposed to receive by the time they are two years old, and did not find any link between those vaccines and increased risk for childhood learning and developmental disorders.

Immunization has dramatically reduced the incidence and severity of childhood illnesses. Community, or “herd” immunity — when the number of vaccinated individuals reaches a critical mass, effectively stamping out the occurrence of the disease — can protect those who were never vaccinated, but it should not be taken for granted. After Wakefield suggested the link between vaccines and autism, parents started electing to forgo vaccinating their children. Years later, whooping cough, a disease that had previously been controlled through vaccination, reemerged with a vengeance. By 2012, the incidence of whooping cough had tripled over the past five years, showing just how tenuous community immunity can be, and reinforcing the importance of vaccination.

The researchers of the current study note that children come into contact with hundreds of different viruses in their first two years of life, so it is unlikely that the extra antigen exposure through vaccination would make a difference in their development. Considering how little we know about the origin of autism spectrum disorders, however, they add that we cannot rule out potential environmental contributions — but vaccines probably have little to do with it.