Children with inherited disorders tolerate routine vaccines as well as healthy children

Klein NP. Pediatrics. 2011;doi:10.1542/peds.2010-3706.

Children with inborn errors of metabolism who received vaccines on similar schedules as healthy infants did not have higher rates of vaccine-associated adverse events, according to results of a recent study published online.

Study findings indicate that children with inborn errors of metabolism (IEM) who received vaccines on the same immunization schedule as healthy infants do not appear at higher risk for serious adverse events. Immunization was also not associated with significant increases in ED visits or hospitalizations during the month after vaccination, according to Nicola Klein, MD, PhD, a researcher of the study and co-director of the Kaiser Permanente Vaccine Study Center.

This study of 271 vaccinated children with IEM did not detect such an association for most children in the 30 days after vaccination, including children aged younger than 1 year with IEM. The study is among the first to study immunization rates and vaccine safety in children with these conditions, which put them at high risk for vaccine-preventable diseases. Although each condition is individually rare, it is estimated that the collective birth prevalence is one in 2,500 to 5,000 live births, according to the researchers.

“It’s important to note that children with inherited metabolic disorders are particularly vulnerable to metabolic stress, including fever that results from infections and inflammatory processes, as well as vaccine-preventable diseases,” Klein said in a press release. “This study adds important information to the evidence base because it’s among the largest and thus perhaps gives us the best look at this to date. The results suggest that routine vaccination of children with IEM is safe, but we recognize that larger studies are needed because these conditions are so rare.”

Researchers grouped children with IEM into three groups — sickest, chronic and stable. They identified children aged up to 18 years who were assigned an IEM diagnosis from 1990 to 2007. Researchers assessed immunization rates by comparing infants with inborn IEMs with matched healthy controls. Researchers then assessed for vaccine-related adverse events, defined as an ED visit or hospitalization, by comparing days 0 to 30 post-vaccination vs. 31 to 70 days post-vaccination among all children with IEM who were vaccinated. This was done to allow evaluation of adverse events that could be caused by inactive and live viral vaccines. They also examined the vaccination period from 0 to 14 days post-vaccination as secondary analyses.

Results of the secondary analyses indicated that there may be increased rates of hospitalizations 2 weeks after vaccination for the sickest children aged 1 to 4 years. The researchers said there may be a subset of more fragile children with inborn IEM at increased risk for adverse events during the immediate post-vaccination period.

The study researchers said this finding should be interpreted cautiously because of the sparse data with a small number of hospitalizations. In addition, there is not a clear association with any particular vaccine(s), the long time period of which these hospital events occurred (17 years), and there is not a corresponding increase in ED visits during the post-vaccine days of 0 to 14.

The study findings also indicate some evidence of increased ED visits during the 2 weeks after vaccination for children aged 0 to 18 years in the stable group, but the small numbers of events (13 during the post-vaccine days of 0-14) occurred over a long period of time. The lack of a corresponding increase in hospitalizations for this group is reassuring because it suggests that ED events were not serious enough to result in hospitalization, the researchers said.

The AAP recommends routine vaccination for children with IEM because infants with underlying inherited metabolic disorders are especially vulnerable if unprotected against vaccine-preventable diseases.

Disclosure: The study was funded by the Clinical Immunization Safety Assessment through a subcontract with America’s Health Insurance Plans under contract from the CDC. Drs. Klein and Baxter report research support from Merck & Co., Novartis, GlaxoSmithKline, Pfizer and Sanofi-Pasteur.

In 2000, Hannah Poling, a 19-month-old child with a mitochondrial enzyme deficiency, received five shots against nine infectious diseases. Soon thereafter, she regressed neurologically and significantly. Her parents believed that this regression was caused by vaccines, not merely temporally associated with them. Her case, which received national attention, raised the question of whether children with mitochondrial enzyme deficiencies should receive vaccines on a different schedule than healthy children. The study by Nicola Klein and co-workers provides further evidence that children with mitochondrial enzyme deficiencies can receive routine vaccinations at the current schedule safely.

– Paul A. Offit, MD
Infectious Diseases in Children Editorial Board member

Disclosure: Dr. Offit reports no relevant financial disclosures.

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