SSPE Risk After Age 5 Measles Infection
The statement is correct: SSPE risk after measles infection acquired at age 5 or older is extremely low and not a realistic clinical concern, as the overwhelming burden of SSPE comes from measles infection in infancy and early childhood, particularly under age 2 years. 1, 2
Age-Stratified Risk Profile
The risk of SSPE is dramatically age-dependent at time of measles infection:
Infants under 12 months face the highest risk at approximately 1:609 to 1:1,700 cases of measles, representing an 18-fold increased risk compared to older children 3, 4, 5
Children under 5 years have an overall SSPE risk of 1:1,367 to 1:3,300 measles cases 3, 4
Children 5 years and older have negligible documented SSPE risk in the literature, with virtually all reported cases having contracted measles before age 5 1
Clinical Reality of SSPE Burden
The epidemiologic data consistently demonstrates where SSPE cases originate:
71% of SSPE cases had documented measles-like illness, and all 12 of these cases occurred in children who had measles prior to 15 months of age 4
The highest risk population is children who contract measles when they are less than 5 years of age, with particular concentration in those infected under age 2 1, 2
SSPE is reported in 6.5 to 11 per 100,000 measles cases overall, but this risk is heavily concentrated in the infant and toddler population 1
Why Age Matters Biologically
The age-dependent risk likely relates to:
Immune system maturity at time of measles infection affects viral clearance and persistence 1
Younger children have developing immune systems that may be less capable of completely clearing measles virus from the central nervous system, allowing persistent infection that manifests years later as SSPE 6, 7
Clinical Implications
For practical clinical decision-making:
SSPE counseling and concern should focus on unvaccinated infants and toddlers exposed to measles, not older children or adults 4
The latency period from measles infection to SSPE onset averages 9.5 years (range 2.5-34 years), meaning SSPE typically presents in school-age children or adolescents who had measles as infants 4
When evaluating a patient with suspected SSPE, the critical history is whether they had measles infection (recognized or unrecognized) during infancy or early childhood, not recent measles exposure in older age 6, 4
Prevention Focus
Measles vaccination remains the only effective prevention strategy for SSPE and has essentially eliminated SSPE in countries with high vaccination coverage 6, 8
Protection of unvaccinated infants requires either avoidance of travel to endemic areas or early vaccination prior to travel at age 6-11 months 4
The MMR vaccine does not increase SSPE risk; when rare cases occur in vaccinated individuals, evidence indicates they had unrecognized measles infection before vaccination 6, 7