estimated that 53.6 percent of adolescents between 13 and 17 years of age had received at least one dose of the MCV4 vaccine (CDC, 2010).

ENCEPHALITIS AND ENCEPHALOPATHY

Epidemiologic Evidence

The committee reviewed one study to evaluate the risk of encephalitis or encephalopathy after the administration of meningococcal vaccine. This one controlled study (Ward et al., 2007) contributed to the weight of epidemiologic evidence and is described below.

Ward et al. (2007) conducted a self-controlled case-series study in children (2 to 35 months of age) residing in the United Kingdom or Ireland between October 1998 and September 2001. The British Pediatric Surveillance Unit distributed monthly surveillance surveys to pediatricians in order to identify children with encephalitis, or suspected severe illness with fever and seizures. The questionnaires were reviewed by a physician to confirm patients met the case definition of severe neurologic disease (encephalitis or febrile seizures). Vaccination histories of confirmed cases were obtained from the child’s general practitioner by the Immunization Department, Health Protection Agency, Centre for Infections, London. The risk periods considered were 0–3 and 0–7 days after meningococcal C conjugate vaccination; each child was categorized as having been vaccinated or unvaccinated, and with disease or without disease based on dates of vaccine administration and disease episodes. A total of 50 children (2 to 11 months of age) and 107 children (12 to 35 months of age) with confirmed severe neurologic disease were included in the analysis. The analysis was stratified by age group: 2–11 and 12–35 months. No cases were observed in the 0–3 day risk period for both age groups. For the 0–7 day risk period, no cases were observed for the 2- to 11-month age group but one case was observed for the 12- to 35-month age group.

The study did not find a significant association with any manifestation of encephalopathy. The relative risk of severe neurologic disease in the 0–7 day risk period after meningococcal C conjugate vaccination was estimated at 1.28 (95% CI, 0.17–9.75). As evidenced by the wide confidence interval, the sample size is not large enough to get a more precise estimate of the relative risk. The authors concluded that administration of meningococcal C conjugate vaccine is not associated with an increased risk of severe neurologic disease within 0 to 7 days of vaccination.



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