Risk of SSPE from MMR Vaccine
The MMR vaccine does not cause SSPE—the risk is essentially zero. 1, 2, 3
The Evidence is Definitive
The Advisory Committee on Immunization Practices (ACIP) states unequivocally that administration of live measles vaccine does not increase the risk for SSPE, even among persons who have previously had measles disease or received live measles vaccine. 1, 2, 3
When rare SSPE cases have been reported in vaccinated children with no known measles history, the evidence indicates these children had unrecognized measles infection before vaccination, and the SSPE resulted from that natural infection, not the vaccine. 1, 2, 3
What Actually Causes SSPE
- Wild-type measles virus infection causes SSPE, not measles vaccination. 2, 3
- The true risk of SSPE following natural measles infection is approximately 4-11 per 100,000 measles cases, but this substantially underestimates actual risk because only about 11% of measles infections are officially reported. 4
- Measles vaccination is the only effective prevention strategy for SSPE. 2, 3, 4
The Protective Effect of Vaccination
- Measles vaccination substantially reduces the occurrence of SSPE, as evidenced by near elimination of SSPE cases after widespread measles vaccination. 1, 2, 3
- In England and Wales, there was an average annual decline of 14% in SSPE onset between 1990-2002, consistent with declining measles incidence due to high MMR coverage. 5
- Brain biopsy specimens from cases with vaccination history but no known measles confirmed wild-type measles virus, not vaccine strain. 5
Virological Confirmation
- When brain biopsies have been performed on suspected vaccine-associated SSPE cases, nucleotide sequence data consistently confirms wild measles virus infection, not vaccine strain. 5
- This provides definitive proof that even in vaccinated individuals who develop SSPE, the causative agent is wild-type virus from unrecognized natural infection. 5
Critical Distinction: Not "1 in a Million"
There is no "1 in a million" risk of SSPE from MMR vaccine—the vaccine prevents SSPE rather than causing it. 1, 2, 3 The "1 per million" figure you may have encountered refers to anaphylactic reactions to measles-containing vaccine (less than 1 case per 1 million doses), which is an entirely different adverse event. 1
Common Pitfall to Avoid
Do not confuse SSPE with acute post-vaccination encephalopathy, which if it were to occur (extremely rare at approximately 1 per 2 million doses), would present around 10 days after vaccination, not years later. 2 SSPE has a latency period of 2.7 to 23.4 years after measles infection. 5