In 1988, the first conjugate vaccine was approved for use in the U.S. It was intended to protect infants and young children against Haemophilus influenzae type b. Since that time the vaccine has been approved in most developed countries -- such as Denmark and Israel where the vaccine was added to their national vaccine programs in 1993 and 1994, respectively.
Starting in the later 1980’s, there was a marked increase in the reported prevalence of autism spectrum disorders among children in the U.S. A similar increase was seen in Denmark and Israel starting approximately 5years later. The continuation of the trend toward increased rates of autism spectrum disorders could be further explained by increased usage of the vaccine.
According to a study reprinted on the website Green Med Info:
“Conjugate vaccines fundamentally change the manner in which the immune systems of infants and young children function ... conjugate vaccines may have disrupted evolutionary forces that favored early brain development over the need to protect infants and young children from capsular bacteria.”