Is the risk of Subacute Sclerosing Panencephalitis (SSPE) due to the Measles, Mumps, and Rubella (MMR) vaccine or because of it?

SSPE Risk: Caused by Wild Measles Infection, NOT the MMR Vaccine

The MMR vaccine does not cause SSPE—it prevents it. SSPE is caused exclusively by wild-type measles virus infection, and vaccination has nearly eliminated this devastating disease in highly vaccinated populations. 1

The Evidence is Unequivocal

MMR Vaccine Does NOT Cause SSPE

• The ACIP definitively states that MMR vaccine administration does not increase the risk for SSPE, even among persons who have previously had measles disease or received live measles vaccine. 1
• The vaccine-strain measles virus does not cross the blood-brain barrier and does not establish CNS infection like wild-type virus does. 1
• The MMR vaccine contains live attenuated viruses that replicate at the injection site and regional lymphoid tissue to generate systemic immunity without CNS penetration. 1

Wild Measles Virus IS the Cause

• SSPE is caused by persistent wild-type measles virus infection in the CNS, occurring approximately 4-11 per 100,000 measles-infected individuals. 2
• Wild-type measles virus can cross the blood-brain barrier and cause CNS disease including acute encephalitis and SSPE, but vaccine-strain viruses do not behave this way. 1
• The risk of SSPE following natural measles infection is 4.0 per 100,000 cases (and 18 per 100,000 if measles occurs under age 1 year). 3, 4

The Vaccine Actually Prevents SSPE

• Measles vaccination substantially reduces the occurrence of SSPE, as evidenced by near elimination of SSPE cases after widespread measles vaccination. 1
• The risk after vaccination is no greater than 0.14 per 1,000 doses—approximately 30-fold lower than after natural measles infection. 3, 4
• England and Wales data show an average annual decline of 14% in SSPE onset following high MMR coverage, with the most recent recorded measles infection leading to SSPE occurring in 1994. 5

Critical Clinical Context: Addressing the Confusion

When SSPE Occurs in Vaccinated Children

• When rare SSPE cases have been reported in vaccinated children with no known measles history, evidence indicates these children had unrecognized measles infection before vaccination, and the SSPE resulted from that natural infection, not the vaccine. 1
• Brain biopsy specimens with nucleotide sequencing from vaccinated children who developed SSPE have confirmed wild-type measles virus, not vaccine strain. 5
• Four children in England and Wales with vaccination history but no documented measles had brain biopsies showing wild-type measles strain. 5

Timing Distinguishes Vaccine Events from SSPE

• SSPE occurs a mean of 7.0 years after natural measles infection (range 2.7 to 23.4 years). 6, 5
• Any true vaccine-related neurological event would occur around 10 days post-vaccination (encephalopathy risk approximately 1 per 2 million doses), not years later. 1
• At one year after MMR vaccination, a child is well beyond the window for vaccine-related adverse events, which cluster in the first 2-3 weeks. 7

Common Pitfalls to Avoid

Do Not Confuse SSPE with Other Post-Vaccination Events

• Febrile seizures occur 5-12 days after MMR at approximately 1 per 3,000 doses but do not lead to residual neurologic disorders or SSPE. 7
• Acute post-vaccination encephalopathy (if it occurs at all) presents around 10 days after vaccination, not one year later. 7

Do Not Delay Vaccination Due to SSPE Concerns

• The only proven prevention strategy for SSPE is measles vaccination. 1
• The CDC and AAP recommend all children receive MMR vaccine regardless of family history of SSPE, as it is the most effective prevention strategy. 2
• Lack of measles vaccination is the dominant immune risk factor for SSPE, as measles infection itself is the prerequisite. 2

Public Health Impact

Vaccination Has Nearly Eliminated SSPE

• Successful measles immunization programs have led to near elimination of SSPE in countries with high vaccination coverage. 1, 8
• The prevention of endemic measles circulation in England and Wales through high MMR coverage resulted in near elimination of SSPE. 5
• The observed downward trend in SSPE incidence since 1969 directly correlates with widespread measles vaccination. 6

The Risk of Declining Vaccination Coverage

• Recent declines in MMR vaccine coverage with associated increases in localized measles outbreaks are of significant concern. 5
• Infants under age 1 year (too young to be vaccinated) have the highest risk of SSPE if they contract measles—18 per 100,000 cases. 3, 4
• High vaccine coverage is essential to protect indirectly those most vulnerable to SSPE through herd immunity. 5