A fatal complication of measles that can occur years after the patient is infected with the contagious virus is more common than previously thought, findings of a new study have revealed.

The deadly complication is known as subacute sclerosing panencephalitis (SSPE), a progressive neurological disorder marked by inflammation in the brain. The condition occurs when the measles virus stays in the brain for years after a young patient is infected and has recovered.

Researchers explained that the measles virus gets all over the body, but a surprising amount goes to the patient's central nervous system. Although in most people, the immune system clears the virus, some do not totally get rid of the virus. In the case of SSPE, the virus that has gone to the brain becomes active again.

Those with SSPE tend to die within a year or two after diagnosis. Some patients may live longer, but the condition is always fatal.

Researchers previously thought that the likelihood for post-measles SSPE to occur was one in 100,000, but new analysis suggested that one in 1,387 children who were infected with measles before reaching 5 years old have a chance of developing SSPE. The risk tends to be higher in younger measles patients, as SSPE is likely to strike one in 609 of those who contract the virus before age 1.

For the new study, James Cherry of the University of California, Los Angeles medical school and colleagues identified 17 cases of SSPE in California between the years 1998 and 2015. They found that children on average get diagnosed with SSPE at age 12, but the diagnosis was also made in individuals as young as 3 and as old as 35 years old. Of the 17 identified cases, 16 were fatal. One is now receiving hospice care.

"It takes having had measles many years before," Cherry said, adding that many more cases across the U.S. may have gone unreported.

The researchers said that the findings highlight the need why parents need to make sure their children receive two doses of the measles, mumps and rubella (MMR) vaccine. Measles is a contagious disease that can easily spread, but immunization offers a means to prevent infection. Kids infected by measles are often those who were not vaccinated.

"The answer is good public health," Cherry said. "You need to vaccinate everybody and create herd immunity so that you protect those most vulnerable to measles and those at greatest risk of SSPE."