Hypothesis: Conjugate vaccines may predispose children to autism spectrum disorders

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Hypothesis: Conjugate vaccines may predispose children to autism

spectrum disorders. <http://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.