One of the most common concerns about immunizations is that they may be linked to higher rates of autism in children. This is because signs of autism sometimes appear at the same time children receive certain vaccinationsespecially the vaccine for measles, mumps, and rubella (MMR).
A study published in 1998 suggested a possible link between autism and the MMR vaccine, but this study was rejected by every major health organization, including the American Association of Pediatrics (AAP), the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO). No study since then has been able to find clear evidence linking the MMR vaccine and autism and the 1998 study was formally retracted in 2004.
There also have been recent concerns about the use of thimerosal, which is an organic mercury compound that has been used as a preservative in vaccines since the 1930s, suggesting that it may be responsible for autism in children. In 2004, the Institute of Medicine issued a report demonstrating that thimerosal does not cause autism. To reduce children's exposure to mercury, the use of thimerosal has declined since 1999 and today, most vaccines for infants and young children do not contain the compound. Recent studies also have shown no developmental or behavioral problems in children who received vaccines containing thimerosal.
One reason that rates of autism have increased is that the definition of autism has broadened and more children are now diagnosed with the condition. Another reason is that greater awareness of the disorder among parents and health professionals has led to earlier evaluation and more diagnoses.
It's important to know that the average age of an autism diagnosis is the same in both children who have received the MMR vaccine and children who have not received the vaccine. And researchers are discovering that subtle signs of autism start appearing very early in life, sometimes even in infancy. Current belief among most medical professionals is that any connection between autism and the MMR vaccine is simply a coincidence.