Vaccination in children with inborn errors of metabolism.

Inborn errors of metabolism (IEMs) are a large group of very heterogeneous diseases, and the impact of the available vaccines on children with IEMs may vary depending on the child's metabolic characteristics. The main aim of this review is to re-analyse the administration of vaccines to such children in the light of the most recent data. As a whole, these indicate that children with stable or slowly progressing IEMs can receive the recommended schedules of all of the recommended vaccinations. However, vaccines should be administered more cautiously to children with IEMs associated with a significant risk of morbidity and/or mortality with catabolic events: i.e. under strict medical supervision, and only when the children are clinically well and their metabolic condition is acceptably controlled. Furthermore, a number of IEMs have been associated with immune deficiency although, in most cases, the immunological abnormalities disappear or are significantly reduced when the metabolic defect is corrected. The response to vaccines is therefore unpredictable, but it is reasonable to think that it may be inadequate in children with the most severe immune defects. In addition to defective protection, vaccines administered to children with IEM and severe immunodeficiency can actually cause the disease they were meant to prevent. This explains why experts suggest that vaccines based on live attenuated viruses should not be given to such children, although all of the other vaccines can be administered without limitation regardless of the type of immune defect. Nevertheless, only specific multicentre studies will make it possible to say when and how to use vaccines in children with different types of IEM in order to protect them from vaccine-preventable diseases without any risk of worsening their metabolic situation.