Risk of SSPE in the General Population
No, the risk of SSPE is not "one in a million" in the general population—it's actually much higher at approximately 4-11 per 100,000 measles cases, which translates to roughly 1 in 10,000 to 1 in 25,000 measles infections. 1, 2
The Critical Context: Underreporting Makes the True Risk Even Higher
The commonly cited figures substantially underestimate the actual risk because measles cases are dramatically underreported. 3
- Only about 11% of actual measles infections are officially reported to health authorities 3
- Before the 1963 vaccine, approximately 400,000 cases were reported annually in the U.S., but the true number approached 3.5 million cases per year 3
- When you account for this underreporting, the real-world risk of SSPE per measles infection is considerably higher than the published estimates suggest 3
Age-Specific Risk: The Highest Danger Period
The risk is dramatically elevated for young children, making the "one in a million" characterization particularly dangerous misinformation:
- Children who contract measles before age 5 have the highest risk of developing SSPE 2
- Infants who contract measles under 1 year of age face an SSPE risk of approximately 18 per 100,000 cases (roughly 1 in 5,500) 4
- This is nearly 5 times higher than the overall population risk 4
Current U.S. Context: Near Elimination Through Vaccination
In the current U.S. general population with high vaccination coverage, SSPE has been essentially eliminated: 1
- Widespread measles vaccination has nearly eradicated SSPE from the United States 1
- The disease only occurs following natural measles infection, never from the vaccine itself 5, 6
- MMR vaccine does not increase SSPE risk, even in persons who previously had measles or received prior measles vaccine 6, 3
The Global Reality: Risk Remains Significant
The risk is not theoretical—it remains a significant global health concern:
- Recent increases in measles cases worldwide have led to subsequent SSPE cases in various regions 7
- Reduced vaccination coverage since COVID-19 will likely accelerate future SSPE risk 7, 8
- Children in areas with poor vaccination coverage face ongoing substantial risk 2
Clinical Implications: Why This Matters
SSPE is a devastating, progressive, and almost universally fatal disease: 8
- It causes progressive neurological deterioration leading to vegetative state and death 8
- There is no cure—only supportive care and symptomatic management 7, 2
- The disease typically presents 7-10 years after measles infection 8
The Only Prevention Strategy
Measles vaccination is the only effective prevention for SSPE and dramatically reduces risk compared to natural infection: 6, 3, 9