Dispelling an incorrect myth, researchers have said that there is no evidence of a correlation between autism and vaccines. They arrived at this conclusion after reviewing a number of epidemiological and biological studies at the Children's Hospital of Philadelphia.
"When one hypothesis of how vaccines cause autism is refuted, another invariably springs up to take its place," said Dr. Paul Offit, the author of the study published online in the journal Clinical Infectious Diseases.
He cautioned that immunization rates have been reducing due to fears about vaccines, and, thus public health is getting affected.
He attributed the current increase in Haemophilus influenzae cases in Minnesota, and last year's measles outbreak in California, to vaccine refusal.
It was way back in 1998 when a study in The Lancet suggested a link between the combination measles-mumps-rubella (MMR) vaccine and autism.
To see whether there was any truth in the controversy thus raised, Dr. Offit and his colleague Dr. Jeffrey Gerber reviewed over a dozen large studies.
Conducted in five different countries, the studies used different methods to address the issue.
The researchers found that no data supported the association between the MMR vaccine and autism.
Following their observations, the researchers concluded that the correlation between MMR vaccine and the appearance of autism symptoms was merely coincidental because the vaccine was given at the age when autism symptoms usually appear.
Also hypothesized as a cause has been the ethylmercury-containing preservative thimerosal, which was used in vaccines for over 50 years.
However, the current study shows that the presence or absence of thimerosal in vaccines did not affect autism rates.
It has also been suggested that the simultaneous administration of multiple vaccines overwhelms or weakens the immune system.
However, the authors of the present study note that children's immune systems routinely handle much more than the relatively small amount of material contained in vaccines.
They even say that present-day vaccines contain many fewer immune-triggering components than those from decades past, and, regardless, autism is not triggered by an immune response.
With outbreaks of vaccine-preventable diseases on the rise due to some worried parents choosing not to vaccinate their children, Dr. Offit said: "Parents should realize that a choice not to get a vaccine is not a risk-free choice. It's just a choice to take a different, and far more serious, risk."
The research paper has been published under the auspices of the Infectious Diseases Society of America (IDSA), a professional society representing more than 8,600 physicians and scientists in Arlington, Virginia.