Hypothesis: Conjugate vaccines may predispose children to autism spectrum disorders

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Hypothesis:

Conjugate vaccines may predispose children to autism spectrum

disorders.

www.ncbi.nlm.nih.gov/pubmed/21993250

Richmand BJ.

Med Hypotheses. 2011 Oct 10.

The first conjugate vaccine was approved for use in the US in 1988 to

protect infants and young children against the capsular bacteria

Haemophilus influenzae type b (Hib). Since its introduction in the US,

this vaccine has been approved in most developed countries, including

Denmark and Israel where the vaccine was added to their national vaccine

programs in 1993 and 1994, respectively. There have been marked increases

in the reported prevalence of autism spectrum disorders (ASDs) among

children in the US beginning with birth cohorts in the late 1980s and in

Denmark and Israel starting approximately 4-5years later. Although these

increases may partly reflect ascertainment biases, an exogenous trigger

could explain a significant portion of the reported increases in ASDs. It

is hypothesized here that the introduction of the Hib conjugate vaccine

in the US in 1988 and its subsequent introduction in Denmark and Israel

could explain a substantial portion of the initial increases in ASDs in

those countries. The continuation of the trend toward increased rates of

ASDs could be further explained by increased usage of the vaccine, a

change in 1990 in the recommended age of vaccination in the US from 15 to

2months, increased immunogenicity of the vaccine through changes in its

carrier protein, and the subsequent introduction of the conjugate vaccine

for Streptococcus pneumoniae. Although conjugate vaccines have been

highly effective in protecting infants and young children from the

significant morbidity and mortality caused by Hib and S. pneumoniae, the

potential effects of conjugate vaccines on neural development merit close

examination. Conjugate vaccines fundamentally change the manner in which

the immune systems of infants and young children function by deviating

their immune responses to the targeted carbohydrate antigens from a state

of hypo-responsiveness to a robust B2 B cell mediated response. This

period of hypo-responsiveness to carbohydrate antigens coincides with the

intense myelination process in infants and young children, and conjugate

vaccines may have disrupted evolutionary forces that favored early brain

development over the need to protect infants and young children from

capsular bacteria.