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Evaluation of Immunization Rates and Safety Among Children with Inborn Errors of Metabolism

Posted Nov 01 2009 10:01pm

Ever since the Hannah Poling case became public, and especially give the way in which David Kirby has presented the case, there has been a question of whether vaccines can cause regressions in children with inborn errors of metabolism (mitochondrial disorders are a subset of these).

I discussed one very recent paper Fever Plus Mitochondrial Disease Could Be Risk Factors for Autistic Regression. Commenter and LBRB blogger Joseph made the very correct observation then:

I’d say it’s potentially interesting, but limited. In order to tell that something is a risk factor, you need a case-control study.

More specifically, can self-selection bias be discounted in this study?

It is encouraging to see that such studies into this question are being staged. Here is the abstract from a study presented 2009 Infectious Diseases Society of America titled, Evaluation of Immunization Rates and Safety Among Children with Inborn Errors of Metabolism.

Abstract

Background: Children with metabolic disorders are a potential high-risk group for vaccine-preventable diseases. Despite recommendations that they receive all routine immunizations, information regarding both immunization rates and safety data within this population is lacking.
Methods: Using Northern California Kaiser Permanente’s (NCKP) integrated electronic medical record, we identified children up to age 18 years who had an inborn error of metabolism (IEM) from 1990 to 2007. We assessed immunization rates among a subset of infants with IEM born at NCKP who were members until age 3 years matched to healthy infants (1:20), comparing both immunizations received by age 2 years and timing for receipt of vaccines. We next separately assessed for adverse events after immunization by using self-controlled analyses among all children up to age 18 years with an IEM who received at least 1 vaccine at any time, comparing emergency room visits and hospitalizations during post-vaccine days 0-30 to post-vaccine days 31-60.
Results: We identified 79 infants with IEM who were born and remained a member of NCKP at age 3 years. Compared to 1580 matched controls, there was no difference in the proportion of children with IEM up to date for vaccines at 2 years, nor was there any delayed receipt of recommended vaccines during the first year. We also preliminarily identified 322 children with IEM who received any vaccine. Preliminary analysis in this group did not detect an increase in emergency room visits [rate ratio (RR) 0.83, 95% confidence interval (CI) 0.60, 1.14] or hospitalizations (RR 1.1, 95% CI 0.9, 1.4) during the 30 days after vaccination compared to post-vaccine days 31-60.
Conclusion: Children with metabolic diseases in this cohort were vaccinated at rates comparable to healthy children. Although sample size is a limitation, preliminary evidence does not suggest an association between vaccination and an increased risk for serious adverse events.

Emphasis added.

A news story on the subject quoted the session chair where the study was presented:

“These findings are very reassuring,” said Larry Pickering, MD, National Immunization Program, Centers for Disease Control and Prevention, and Emory University, Atlanta, Georgia, who moderated the session at which the study was presented.

“Most of us who take care of kids with inborn errors of metabolism think vaccination is one of the best interventions we can offer them,” he said. “They are at increased risk for devastating complications, even death, from the diseases that the vaccines prevent.”

This is reassuring. Preliminary, yes. I can already see the criticisms, both legitimate and otherwise, that will be levied against this study. but potentially very reassuring. Vaccines are one of the front line interventions in protecting people with mitochondrial disorders.

Let’s see if I can predict the criticisms:

1) not peer reviewed
2) many authors received grant money from vaccine manufacturers.
3) the sample size is small (79 infants)
4) the number of infants with mitochondrial disorders is even smaller (7)
5) it would be good to see a comparison of hospitalizations in the months previous to immunizations (if possible)
6) the time spanned by the study covers a large change in the immunization schedule. The sample size of infants immunized in the current schedule is likely to be rather small.

The sample size is small, but it would be interesting to see if the prevalence of metabolic disorders has increased over this time span. But, as autism has shown us, the correlation=causation arguments can be shaky at best.

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