NEW ORLEANS (FRONTLINE MEDICAL NEWS) – A fatal complication of measles known as subacute sclerosing panencephalitis (SSPE) can develop years after measles infection and appears to occur much more often than published reports suggest, according to a review of cases in California from 1998 to 2015.

The findings underscore the vital importance of herd immunity by vaccination, Kristen Wendorf, MD , reported at an annual scientific meeting on infectious diseases.

The risk of SSPE, a neurologic disorder that is 100% fatal, decreases with routine measles vaccination, but is of particular concern in unvaccinated infants who contract measles. During the study period, 17 cases were identified, and a subanalysis of data from the California Department of Public Health (CDPH) showed that the incidence of SSPE among measles cases was 1 in 1,367 children under age 5 years and 1 in 609 children under age 12 months at the time of measles disease, said Dr. Wendorf of the CDPH, Richmond, Calif.

The incidence of postmeasles SSPE was previously thought be about 1 in 100,000, according to an IDWeek press release.

“There is no cure for SSPE, and the only way to prevent it is to vaccinate everyone against measles,” the release stated.

The cases in the current study were among children with a clinically compatible illness, and either measles IgG antibody detected in cerebrospinal fluid, a characteristic pattern on electroencephalography, typical histologic findings on brain biopsy, or medical record documentation of SSPE-related complications. They were identified based on death certificates, reports from the Centers for Diseases Control and Prevention, or through investigations for undiagnosed neurologic disease. Twelve of the 17 affected children had a clinical history of a febrile rash illness compatible with measles, and all 12 of those experienced illness before age 15 months and before measles vaccination.

Most (67%) were living in the United States when they had measles, Dr. Wendorf said at the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society.

The median age at diagnosis of SSPE was 12 years, although the range was 3-35 years, and the mean latency period was 9.5 years. In many cases, long-standing cognitive or motor problems were experienced prior to diagnosis, she noted.

The findings suggest that SSPE is more common than previously recognized in unvaccinated children with measles during infancy, Dr. Wendorf said.

Protection of infants younger than 12-15 months of age – before the time when measles vaccine is routinely administered – and in those who can’t be vaccinated because of immune system disorders requires avoidance of travel to endemic areas. Parents also may consider early vaccination prior to such travel.

Further, clinicians should be aware of the risk of SSPE in patients with symptoms suggestive of the disease. This is true even among older patients in whom no specific history of measles infection is known, she said.

In the press release, coauthor James D. Cherry, MD , professor of pediatrics at the University of California, Los Angeles, further stressed the importance of protecting unvaccinated infants.

“Parents of infants who have not yet been vaccinated should avoid putting their children at risk. For example, they should postpone trips overseas – including to Europe – where measles is endemic and epidemic until after their baby has been vaccinated with two doses,” he said. “It’s just not worth the risk.”

The authors reported having no disclosures.