The Danish study followed nearly 750,000 children, comparing the risk of developing type 1 diabetes between vaccinated and non-vaccinated children, and found no evidence of an association between common vaccines and the disease.
"Overall, there were no more cases of diabetes among the vaccinated children than in the unvaccinated children," says researcher Anders Hviid, of Statens Serum Institute in Copenhagen, Denmark.
The findings appear in the April 1 issue of TheNew England Journal of Medicine.
Type 1 diabetes (formerly known as juvenile or insulin-dependent diabetes) occurs when insulin-producing cells in the pancreas are destroyed by the immune system. The exact cause of the disease is unknown, but a combination of genetic and environmental factors is thought to influence the risk of developing the condition.
Diabetes and Vaccination Linked by Timing Alone
Researchers say the fact that type 1 diabetes cases have risen by 3% each year in developed countries over the last 50 years has fueled speculation that various environmental factors, such as diet, lifestyle, and exposure to infectious agents, early in life might play an important role in the development of the disease.
In addition, the rising incidence of type 1 diabetes in recent years has coincided with the introduction of a growing number of childhood vaccines. Current guidelines for infant vaccination call for up to 18 injections that protect against 12 different infectious diseases by the time children reach 2 years of age.
"There has been this temporal association between increased immunization and the occurrence of type 1 diabetes," says Richard Insel, MD, executive vice president for research at the Juvenile Diabetes Research Foundation. He says the groups that say type 1 diabetes is caused by immunization base this on very little data.
"In my opinion, this article is very important because it will lay to rest the accusations that have been made suggesting that childhood immunization causes childhood diabetes," Insel tells WebMD.
Vaccinations Don't Increase Diabetes Risk
In the study, researchers looked at all the children born in Denmark from 1990 to 2000 for whom detailed information on vaccinations and type 1 diabetes was available.
Among this group of 739,694 children, 681 were diagnosed with type 1 diabetes. Researchers compared the risk of developing the disease among unvaccinated children with children who had received at least one dose of the following common childhood vaccines and combinations:
- Haemophilus influenzae type b
Diphtheria, tetanus, and inactivated poliovirus
Diphtheria, tetanus, acellular pertussis, and inactivated poliovirus
Whole-cell pertussis vaccine
The study showed that there was no significant increase in diabetes risk associated with single or escalating doses of any of the vaccines.
In addition, the study also looked at the period following vaccination and did not find any clustering of diabetes cases in the time period after vaccination.
An increase in the number of new type 1 diabetes cases in children within a few years following vaccination is often cited as a sign that the vaccines might be to blame in triggering the disease, but the study found no such clustering.
Finally, when researchers looked at children who were genetically predisposed for the development of type 1 diabetes because they had a sibling with the disease, they found no increase in risk among those who had been vaccinated compared with unvaccinated high-risk children.
Closing the Door on Vaccine-Diabetes Debate?
Hviid says it is always easier to come up with a hypothesis rather than to refute it, but this study comes as close as possible to closing the door on the debate on whether there's a cause-and-effect relationship between childhood vaccination and the development of type 1 diabetes.
"The design and size of this study makes our results very robust, and we couldn't find any indication of association," Hviid tells WebMD. "I can't see how it's going to be conducted larger or better anywhere else."
In an editorial that accompanies the study, Lynne Levitsky, MD, of Massachusetts General Hospital and Harvard Medical School in Boston, agrees and says the results of study "conclusively demonstrate that there is no relationship between vaccination history and the development of type 1 diabetes.
"The scientific community should now move on to the most important tasks: identifying the genetic, immunologic, and environmental phenomena that are actually responsible for the development of diabetes and finding the means to prevent and treat this chronic disorder," says Levitsky.