Risk of SSPE When Measles is Caught at Age 5
The statement is correct—SSPE risk is dramatically lower when measles is contracted at age 5 or later, with the highest risk occurring when measles infection happens before age 2 years. 1, 2
Age-Stratified Risk Profile
The risk of developing SSPE is strongly age-dependent at the time of measles infection:
- Measles infection under 1 year of age carries a risk 16 times greater than measles contracted over age 5 years 2
- The highest risk occurs in children who contracted measles when they were less than 5 years of age, with 46% of SSPE cases having had measles before age 2 1, 3
- Measles under 1 year specifically carries an 18-fold increased risk (18 × 10⁻⁵) compared to the baseline risk of 4.0 × 10⁻⁵ for all ages 4
Quantifying the Overall Risk
The baseline risk across all ages is approximately:
- 4-11 cases per 100,000 measles infections 5, 6, 4, 2
- This translates to a risk of 4.0 × 10⁻⁵ following measles infection 4
- However, this substantially underestimates actual risk because only 11% of measles cases are officially reported 6
Critical Clinical Context
The latency period between measles infection and SSPE onset averages 7.0 years, meaning SSPE typically manifests years after the initial infection 3. This interval has been increasing over time due to declining measles incidence from vaccination programs 4.
Prevention Remains Paramount
Measles vaccination is the only effective prevention strategy for SSPE and has essentially eliminated the disease in highly vaccinated populations 7, 5, 8. The risk after vaccination (0.14 × 10⁻⁵) is dramatically lower than after natural infection 4, 2.
Important Caveat
The MMR vaccine does not increase SSPE risk, even in those who previously had measles or prior vaccination 7, 8, 6. When rare SSPE cases occurred in vaccinated children without known measles history, evidence indicates these children likely had unrecognized measles infection before vaccination 7, 8.