Measles, Mumps, and Rubella - Centers for Disease Control and ...

Vol. 47 / No. RR-8 MMWR 29In 1994, the IOM noted that most data were from case reports, case series, or uncontrolledobservational studies, and concluded that the evidence was inadequate toaccept or reject a causal relation (150 ).The British National Childhood Encephalopathy Study (NCES) identified a fourfoldelevation in risk for encephalopathy or convulsions among children who receivedmeasles vaccine during 1976–1979, compared with the risk for these conditionsamong unvaccinated children (180). Among previously normal children, the attributablerisk for acute encephalopathy or convulsions was 1 case per 87,000 vaccinations.Findings of a subsequent 10-year follow-up study of persons diagnosed with convulsionsor acute encephalopathy in the NCES indicated little difference in risk forpersisting neurological abnormality among those who had received measles vaccinecompared with those who had not (E. Miller, personal communication).Although cases of encephalopathy have been reported after administration of measles-containingvaccine (181 ), lack of a unique clinical syndrome or specific laboratorytest has hampered causality assessment. However, four independent passive surveillancesystems in the United States (i.e., CDC measles surveillance from 1963 to 1971,the Monitoring System for Adverse Events Following Immunizations [MSAEFI] from1979 to 1990, the Vaccine Adverse Event Reporting System [VAERS] from 1991 to1996, and the Vaccine Injury Compensation Program [VICP]) have reported cases ofencephalopathy in which a similar timing of reported events following vaccine administrationis apparent. In all four case series, onset of encephalopathies follows anon-random distribution with onset approximately 10 days after vaccination, a timingconsistent with onset of encephalopathy after infection with wild measles virus (182 ).Although this pattern may be in part attributable to consistent biases of these passivesurveillance systems, it is also consistent with a causal relationship between measlesvaccine and encephalopathies (183 ). During the period these four systems have collecteddata, 166 cases of encephalopathy occurring 6–15 days after vaccination havebeen identified and an estimated 313 million doses of measles-containing vaccineshave been distributed (i.e., approximately 1 case per 2 million doses distributed).Thus, encephalopathy occurs much less frequently after administration of measlesvaccine than after measles infection.Febrile Seizures and Personal and Family History of ConvulsionsMMR vaccination, like other causes of fever, may cause febrile seizures. The risk forsuch seizures is approximately 1 case per 3,000 doses of MMR vaccine administered(168 ). Studies have not established an association between MMR vaccination and residualseizure disorders (150 ). Although children with personal or family histories ofseizures are at increased risk for idiopathic epilepsy, febrile seizures after vaccinationsdo not increase the probability that epilepsy or other neurologic disorders will subsequentlydevelop in these children. Most convulsions that occur after measlesvaccination are simple febrile seizures, which affect children who do not have otherknown risk factors for seizure disorders.Antipyretics may prevent febrile seizures after MMR vaccination if administeredbefore the onset of fever and continued for 5–7 days. However, antipyretics are difficultto use for this purpose because the onset of fever is often sudden and occursunpredictably. Seizures can occur early in the course of fever. Parents should be vigilantfor fever that occurs after vaccination and should be counseled regarding its