A 1-year-old boy is brought to the clinic for his 12-month
examination. He is healthy, well-nourished, and well-developed and has no significant medical history. His development is appropriate, and he has accomplished all the 1-year milestones. The patient is happy and playful in the examination room, exhibits good eye contact, and makes appropriate attachment with his parents. One of the concerns expressed by the parents has to do with immunizing their child, and they ask about the risk of developing autism with vaccination.
CLINICAL QUESTION
Does the measles, mumps, and rubella (MMR) vaccine that is given at age 12 to 15 months put children at a greater risk of developing a pervasive developmental disorder (PDD), such as autism?
BACKGROUND
Many parents are concerned about the safety of vaccines that are given to their infants and children. In 1998, Dr Andrew Wakefield, a British gastroenterologist, published an article in The Lancet that suggested a link between the MMR vaccine and the development of autism.1 Based on the evaluation of 12 children, Dr Wakefield and colleagues reported that patients could develop intestinal symptoms and subsequent autistic regression following immunization with the MMR vaccine. This led parents in both Europe and the United States to begin questioning vaccines in general and the MMR vaccine in particular. Some parents began to refuse vaccines, fearing that their children would be harmed. Other parents refused the MMR vaccine or any vaccines containing thimerosal, a preservative additive now present only in the influenza vaccine. Following the 1998 study, there was an urgency to prove that vaccines are safe, and numerous studies were undertaken to follow up and validate or invalidate Dr Wakefield's findings. Many parents of children who have autism suspect the MMR vaccine because autism is commonly diagnosed at 15 to 24 months, soon after the MMR vaccine is given.
Another reason to suspect vaccines stems from the fact that the incidence of autism has risen as the immunization rate and the number of immunizations given have increased. Between 1998 and 2007, the number of 6- to 21-year-old patients receiving services for PDD in public special education programs increased from 54,064 to 258,305.2 In 2006, the incidence of autism was 1 in every 110 persons, and this number has continued to rise in the United States. Today, in the United States, children are immunized against 14 diseases by receiving 10 immunizations. After the introduction of vaccines, the incidence of measles, mumps, and rubella dropped 99%.3 This proves the efficacy of the US immunization program.
The true incidence of autism spectrum disorders is likely to range from 30 to 60 cases per 10,000 population, a huge increase over the original estimate 40 years ago of 4 per 10,000 population.4 The increase is largely a consequence of improved ascertainment and a considerable broadening of the diagnostic concept. However, a true risk caused by some yet-to-be-identified environmental risk factor cannot be ruled out.5
SEARCH CRITERIA
AND RESULTS
A search of the peer-reviewed literature was conducted through PubMed, cinahl, medline, the Cochrane Library, and Ovid Evidence-Based Medicine Reviews using the keywords MMR, autism, pervasive developmental disorder, and vaccine adverse reactions. The search was limited to English language, humans, male and female children younger than 18 years, and 1996 to current. Twenty-four citations were identified, of which two case-control studies and two retrospective cohort studies graded level 2 evidence or higher were evaluated. Level 1 evidence on this subject is unavailable, as the performance of randomized controlled trials on children is unethical.