Risk of SSPE in a 15-Year-Old Contracting Measles
Yes, there is a definite risk of SSPE if a 15-year-old contracts measles, though the risk is lower than for younger children—the statement that measles after age 5 carries negligible risk is false. 1
Understanding the Risk Magnitude
The overall risk of developing SSPE following measles infection is approximately 4-11 per 100,000 measles cases 1, with some studies reporting rates as high as 1 in 1,367 for children under 5 years 2. However, age at measles infection significantly modifies this risk:
- Measles contracted under 1 year of age carries a risk 16 times greater than measles contracted over 5 years of age 3
- The calculated risk following measles infection is 4.0 per 100,000 cases overall 3
- Among children who develop SSPE, 71% had measles-like illness prior to 15 months of age, but this does not eliminate risk for older individuals 2
Critical Age-Related Context for a 15-Year-Old
While the highest risk group is children who contract measles before age 5 4, measles vaccination remains the only effective prevention strategy regardless of age 1. The latency period between measles infection and SSPE onset is typically:
- Median of 6-8 years after initial measles infection 1
- SSPE onset generally occurs between ages 5-15 years, with a median age at diagnosis of 12 years (range 3-35 years) 2
- The mean interval is 7.0 years between measles illness and SSPE onset 5
Why This 15-Year-Old Remains at Risk
The risk is not negligible for several reasons:
- SSPE can occur in adults, though less frequently than in those infected during childhood 6
- The disease affects immunologically normal individuals 7
- Male patients have 2.4-2.8 times higher risk than females 2, 3
- The latency period can extend up to 34 years, meaning infection at age 15 could manifest into adulthood 2
Prevention is Critical
The CDC and ACIP definitively recommend catch-up vaccination for adolescents and adults born after 1957 without documentation of two MMR doses or laboratory evidence of immunity 1. This recommendation exists precisely because:
- Measles vaccination has essentially eliminated SSPE in highly vaccinated populations 1
- The risk of SSPE following measles vaccine (0.14-1.1 per million doses) is dramatically lower than following natural measles infection 3, 5
- When rare SSPE cases occur in vaccinated individuals, evidence indicates they had unrecognized measles infection before vaccination 6, 7
Clinical Implications
If this 15-year-old contracts measles without prior vaccination:
- They face the baseline risk of 4-11 per 100,000 measles cases for developing SSPE 1
- This risk is lower than for infants but not negligible 1
- SSPE would likely manifest years later, potentially in their early 20s based on the typical 6-8 year latency 1, 2
- The disease is uniformly fatal in most affected individuals 1, 4
Common Pitfall to Avoid
Do not assume that older age at measles infection eliminates SSPE risk—while the risk decreases with age, it persists throughout life, and the devastating nature of SSPE (progressive neurologic deterioration leading to death) makes prevention through vaccination essential regardless of current age 1, 4.