Background: Insulin-dependant diabetes mellitus (IDDM) is an autoimmune disease that can be altered by immune modulation. NOD mice and BB rats have been used as models of spontaneous IDDM. The development of diabetes in these animals has been altered by several different immune modulators using relatively high doses for the size of the animal. The effect of pharmaceutical doses of vaccines on the development of diabetes in these rodents has not been adequately studied.Methods: I studied the effect of administering killed human vaccines using low concentrations and as few as 3 doses.Results: Administration of human vaccines to diabetic prone newborn animals starting before 2 weeks of age prevented the development of diabetes while administration of the pertussis vaccine starting at 8 weeks of life was associated with an increased incidence of diabetes.Conclusions: Animal studies have demonstrated the timing and content of human vaccines can affect the development of diabetes. Clinical trials of new human vaccines are not designed and generally not powered to detect an effect of immunization on the development of IDDM. These animal toxicology studies indicate that the effect of vaccines on human insulin dependent diabetes needs to be examined.