Has Vaccine Genotype A Been Sequenced in Brain Tissue of SSPE Patients?
No, vaccine genotype A (measles vaccine strain) has never been sequenced in the brain of patients with SSPE—all documented SSPE cases are caused by wild-type measles virus, not vaccine strains. 1, 2, 3
Evidence That Vaccine Strains Do Not Cause SSPE
The CDC definitively states that measles vaccination does not increase the risk for SSPE, and when rare SSPE cases have been reported in vaccinated children without known measles history, evidence indicates these children likely had unrecognized wild-type measles infection before vaccination 1
The vaccine virus does not possess SSPE-prone molecular characteristics that are found in wild-type measles virus 3
Measles vaccination has essentially eliminated SSPE in highly vaccinated populations, demonstrating that the vaccine prevents rather than causes this disease 2
Molecular Evidence Distinguishing Vaccine from SSPE Viruses
All known SSPE viruses have a specific molecular marker in their M protein—the PEA motif (residues P64, E89, and A209)—whereas vaccine strains like Moraten have either SKT (S64, K89, T209) or PKT motifs 4
The PEA motif, particularly the A209 residue, is linked to increased viral spread and appears to be a molecular marker for wild-type measles virus at risk of causing SSPE 4
Measles virus RNA recovered from autopsied brain tissue in SSPE cases demonstrates characteristic mutations including a hypermutated M gene and F protein mutations that confer hyperfusogenic properties, facilitating transneuronal spread—features not present in vaccine strains 3, 5
Antigenic Analysis of SSPE Viruses
Research examining MeV-H genes from brain autopsy tissue of three SSPE patients found that genotype A (along with G3 and F) showed an intact antigenic structure similar to wild-type circulating strains, not vaccine strains 6
SSPE-causing viruses show antigenic properties similar to currently circulating wild-type MeV genotypes, not vaccine genotypes 6
Functional analysis of SSPE MeV-H showed activity in a SLAM/nectin-4-dependent manner, consistent with wild-type virus behavior 6
Clinical Implications
When SSPE is diagnosed, the causative virus is always a mutant form of wild-type measles virus that persisted in the brain following natural measles infection, typically occurring years before symptom onset 2, 5
The only effective prevention strategy for SSPE is measles vaccination, which prevents the initial wild-type measles infection that can lead to SSPE 1, 2, 7
Children who developed SSPE after receiving measles vaccination likely had unrecognized wild-type measles infection before vaccination, and the SSPE resulted from that natural infection, not the vaccine 1, 2