Risk of SSPE After Measles Infection at Age 5
The risk of developing SSPE after contracting measles at age 5 is approximately 1 in 1,700 to 1 in 3,300, which represents a substantial risk that is comparable to the risk of fatal acute measles infection itself. 1
Age-Specific Risk Profile
Children who contract measles before age 5 face the highest risk of developing SSPE compared to older age groups. 2, 3 The specific risk estimates for this age group include:
- German surveillance data (2003-2009) calculated the SSPE risk for children infected with measles below 5 years of age as 1:1,700 to 1:3,300 1
- California data (1988-1991) showed an overall SSPE incidence of 1:1,367 among children under 5 years at time of measles infection 3
- The general population risk across all ages is reported as 6.5 to 11 per 100,000 measles cases, but this is significantly higher in the under-5 age group 2
Critical Age-Related Considerations
The risk is dramatically higher for children infected during infancy (under 12 months), with California data showing a risk of 1:609 for this youngest age group 3. At age 5, the child falls into the high-risk category but not the highest-risk infant category.
Clinical Implications
- SSPE typically develops years after the initial measles infection, with a median latency period of approximately 9.5 years (range: 2.5-34 years) 3
- Among California cases, 71% had documented measles-like illness prior to 15 months of age, and all 12 with known measles history were infected before 15 months 3
- SSPE is invariably fatal in most affected children 2
Prevention Context
Measles vaccination is the only effective prevention strategy for SSPE, and the vaccine does not increase SSPE risk—it prevents it 4, 5. The risk after vaccination is estimated to be no greater than 0.14 × 10⁻⁵, compared to 4.0 × 10⁻⁵ (or 40 × 10⁻⁵ for measles under age 1) after natural measles infection 6.
Important Caveats
- The 1:1,700 to 1:3,300 risk estimate represents the same order of magnitude as the risk of fatal acute measles infection itself, underscoring that SSPE is not a rare complication but a substantial long-term threat 1
- Children in areas with poor vaccination coverage and high HIV prevalence face increased SSPE risk 2
- Males develop SSPE more frequently than females (2.4:1 ratio) 3