Indian Pediatrics 1999; 36:317-318
Measles Vaccination and Risk of SSPE
In fact, the risk of SSPE has been estimated at 8.5 SSPE cases per I million cases of measles for a 6 year period, during which the estimated risk after measles vaccination was 0.7 cases per 1 million cases of vaccine(2). However, it has not been determined with certainty whether SSPE resulted from persistent infection with the attenuated measles virus of the vaccine, from undiagnosed wild type measles infection preceding vaccination or from vaccine failure and subsequent undiagnosed measles(2).
I fully agree that the age of vaccination does not have any bearing on occurrence of SSPE though measles at an early age especially prior to 18 months substantially increases likelihood to have SSPE(2). I also do agree that even if attenuated vaccine strain does occasionally cause SSPE, the markedly reduced incidence of post infections measles encephalitis and the apparent reduction in frequency of SSPE, establish the unequivocal benefit of measles immunization(3).
Ramesh K. Agarwal,
I appreciate Dr. Agarwals pursuit of the link between measles immunization and SSPE. Let me reassure Dr. Agarwal and readers of Indian Pediatrics that there has been no evidence that measles vaccine may cause SSPE. However, SSPE has occurred in many children after receiving measles vaccine and this sequence of events has led to the earlier and erroneous conclusion that the vaccine caused it. Sequence is not sufficient evidence for consequence.
In a report on 81 children with confirmed SSPE, we had documented 17 without past history of clinical measles (or vaccination)(1). This illustrates the phenomenon of subclinical meales, which had occurred in 20 to 40% of children in Vellore region during the premeasles-vaccine era(2). Had any such child been given measles vaccine, the subsequent development of SSPE would naturally be attributed to the vaccine, as has been observed by ourselves and others and pointed out by Agarwal. Actually, the widespread measles immunization in the United State of America has led to the virtual disappearance of SSPE. Since there has been no other plausible explanation for the disappearance of SSPE, this sequence does point to consequence! In one case-control study, measles vaccination was found to be associated with protection against SSPE(3). To the best of my knowledge, no genetic identity of the defective measles virus in the brain tissue of SSPE cases has been shown with the attenuated measles vaccine virus. Biologically it is possible that measles vaccine virus might reach the brain, become defective and chronic and cause SSPE. Until such an incident is detected, we must accept that there is no evidence to believe that measles vaccine may cause SSPE.
Tamil Nadu - 632 002,