BACKGROUND: When measles vaccines were widely introduced in the 1970s, there 
were concerns that they might cause subacute sclerosing panencephalitis (SSPE): 
a very rare, late-onset, neurological complication of natural measles infection. 
Therefore, SSPE registries and routine measles immunization were established in 
many countries concurrently. We conducted a comprehensive review of the impact 
of measles immunization on the epidemiology of SSPE and examined epidemiological 
evidence on whether there was any vaccine-associated risk.
METHODS: Published epidemiological data on SSPE, national SSPE incidence, 
measles incidence and vaccine coverage, reports of SSPE in pregnancy or shortly 
post partum were reviewed. Potential adverse relationships between measles 
vaccines and SSPE were examined using available data.
RESULTS: Epidemiological data showed that successful measles immunization 
programmes protect against SSPE and, consistent with virological data, that 
measles vaccine virus does not cause SSPE. Measles vaccine does not: accelerate 
the course of SSPE; trigger SSPE or cause SSPE in those with an established 
benign persistent wild measles infection. Evidence points to wild virus causing 
SSPE in cases which have been immunized and have had no known natural measles 
infection. Perinatal measles infection may result in SSPE with a short onset 
latency and fulminant course. Such cases are very rare. SSPE during pregnancy 
appears to be fulminant. Infants born to mothers with SSPE have not been 
subsequently diagnosed with SSPE themselves.
CONCLUSIONS: Successful measles vaccination programmes directly and indirectly 
protect the population against SSPE and have the potential to eliminate SSPE 
through the elimination of measles. Epidemiological and virological data suggest 
that measles vaccine does not cause SSPE.