Subacute Sclerosing Panencephalitis: more cases of this fatal disease are prevented by measles immunization than was previously recognized. Bellini WJ, Rota JS, Lowe LE, Katz RS, Dyken PR, Kaki SR, Shieh W-J, Rota PA. Journal of Infectious Diseases 2005;192:1686-1693.
Explanatory note: Subacute sclerosing panencephalitis (SSPE) is a rare fatal illness caused by ongoing measles virus infection of the brain. Symptoms of brain damage usually begin 7 to 10 years after infection. Often death occurs 1 to 3 years after the onset of symptoms. Measles infection at a young age is a risk factor for developing SSPE.
Although there is only one strain of measles, there are variations in the genetic makeup of the virus that allow scientists to determine the geographic origin of a given strain and permit distinguishing vaccine virus from wild type virus.
Decreasing rates of immunization, especially among preschool-age children, led to a resurgence of measles illness in the United States during 1989-1991 following which cases have been few.
What was the risk of subacute sclerosing panencephalitis (SSPE) associated with the resurgence of measles?
The researchers analyzed brain tissue specimens from 12 patients with SSPE referred to the CDC. Additional SSPE cases were found by a literature review, and the case reports were included in the study.
The brain tissue specimens were examined by molecular techniques to detect the measles virus and determine its genetic type.
All of the cases included in the analysis were born in the US during the period of 1989-1991. The cases were confirmed to have had SSPE. Some had no clinical history of having had measles.
Using genetic analysis, the researchers demonstrated that only wild-type measles virus strains caused these cases of SSPE.
The researchers found an incidence off SSPE of 22 per 100,000 cases of measles; adjusting for under-reporting they estimated that the incidence of SSPE was likely to be between 7 and 11 cases per 100,000 cases of measles.
The incidence of SSPE is greater than previously estimated at 8.5 cases per 1,000,000 cases of measles.
Measles vaccine virus was not associated with these cases (or other previously reported cases).
Both cases of SSPE and measles could have been under-reported, but this estimate of risk for SSPE is likely more accurate than previous estimates. The incidence of SSPE during the study period of 1989-1991 may have also been higher than previously because a large proportion of measles cases occurred in children less than two years of age, especially in children less than one year old.
High levels of measles immunization are needed to prevent transmission of measles in communities and to prevent the complications of measles infection. Misinformation about measles vaccine safety caused immunization levels to do down which unfortunately led to resurgence of measles activity in a number of countries.