Vaccines are Safe for Children with Urea Cycle Disorders

NIH sponsored study finds concerns of life-threatening crises after vaccination unfounded

Researchers funded by the National Institutes of Health have found that vaccines are safe for children diagnosed with a group of diseases known as urea cycle disorders.

Urea cycle disorders result when the liver cannot break down ammonia. Ammonia is produced during the digestion of proteins. The disorders stem from a failure to produce any of 6 chemicals, known as enzymes, that remove ammonia from the blood. Treatment for urea cycle disorders involves limiting protein in the diet and treatment with medications that break down ammonia. If urea cycle disorders are untreated, ammonia can reach toxic levels, leading to seizures, comas, and brain damage. Periods of illness or stress may raise ammonia to dangerously high levels.

Funding for the study was provided by the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, the Office of Rare Diseases Research, and National Center for Research Sources, and by the U.S. Centers for Disease Control and Prevention.

"Vaccination stimulates the immune system to recognize disease organisms," said Mary Lou Oster-Granite, Ph.D., a health scientist administrator in the NICHD’s Intellectual and Developmental Disabilities Branch. "There were concerns that vaccination, could, theoretically, provoke an ammonia crisis. The study findings show that those concerns are unfounded."

The research was conducted by Thomas M. Morgan, M.D., and colleagues at Vanderbilt University School of Medicine in Nashville, Tenn, and Children’s National Medical Center in Washington, D.C.

The study appeared in the Journal of American Academy of Pediatrics.

To conduct the study, Dr. Morgan and his colleagues analyzed the medical records of 112 children who had urea cycle disorders. The researchers checked the dates that the children had been vaccinated and also checked to see whether they had experienced any episodes of high ammonia levels after the vaccinations. The researchers did not find any cases where vaccination was followed by an increase in ammonia levels.

The study authors concluded that children with urea cycle disorders should receive the recommended childhood immunizations, provided that their ammonia levels are kept under control and that they have no other medical conditions which would interfere with vaccination.


About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)

The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit the Institute’s Web site at

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