PJM18 - SSPE has been thought to be associated with MMR for a while, but it is now clear that MMR has never (and probably cannot) cause(d) SSPE.
Every SSPE biopsy sample submitted for molecular sequencing has always been wild-type virus and never vaccine strain measles virus. (from www.ncbi.nlm.nih.gov/pubmed/15893837)
6.4. Only wild-type virus sequences have been found in SSPE
The description of specific clades and genotypes of MV has allowed the evaluation of mutations found in the MV RNA sequences from SSPE brain material against wild-type (clades B?G) viruses. All the vaccine viruses are derived from the Edmonston strain (clade A) but no clade A virus has been found in SSPE brain material. The sequences found in SSPE brain are related to the wild-type viruses circulating at the time of initial infection of the child and not to those circulating at the time of onset of symptoms. Hence, the virus which initially infected the child, appears to persist and SSPE is not due to a super-infection by viruses circulating during the onset of symptoms (Jin et al., 2002) (Rima et al., 1995); Rota, personal communication). To the best of the authors? knowledge no vaccine virus, genotype A, sequences have been obtained from SSPE cases. SSPE has been vastly reduced in incidence after successful control of measles by vaccination (Dyken et al., 1989). In contrast, vaccine strains have been identified in MV infections in immuno-compromised patients who died from MIBE (Bitnun et al., 1999) and giant cell pneumonia (Mawhinney et al., 1971).
Even in SSPE cases who did not have any reported measles disease but had measles vaccination, only wild-type measles strains were identified (jid.oxfordjournals.org/content/192/10/1686.long):
Although measles is a monotypic virus, 22 genotypes of wild-type virus are recognized; many genotypes have been associated with endemic circulation of measles virus in certain geographic regions or have been documented in connection with an outbreak or epidemic in an area [4, 5]. The measles vaccine virus strains belong to genotype A and can be distinguished from wild-type virus of the same genotype by means of sequence analysis [6 ?8]. Analyses of measles virus sequences in brain tissue samples obtained from patients with SSPE have identified only wild-type measles virus, and the virus genotypes identified have been consistent with the genotype of measles virus that circulated in the area where the patients lived and to which the patients had been exposed ⩾10 years before the onset of symptoms of SSPE [6, 9 ?13]. Genetic studies have supported epidemiologic evidence that measles vaccine virus does not cause SSPE [6, 14, 15]. In cases of SSPE that developed in children or adults who had no history of measles but who did have a history of vaccination against measles virus, analysis of measles virus sequences derived from the patients confirmed the presence of the wild-type genome, indicating that the individuals had an undiagnosed measles virus infection [6, 7, 9]
MMR does not cause SSPE.