Vaccination supporters say reports that a measles complication, which is 100 percent fatal, is more common than previously thought and underscores the importance of timely vaccination.

It also serves as a reminder for parents to avoid traveling to certain areas with young children.

The new research suggests that these factors could put children at greater risk for the fatal measles complication — subacute sclerosing panencephalitis (SSPE), a fatal neurological disorder that can develop after an individual has measles — than formerly believed.

Read more: Get the facts on measles »

What the data shows

Using data from California, researchers found a rate of SSPE of around 1 in 600 for infants who contract measles before being vaccinated.

This rate was once thought to be 1 in 100,000 among those who got measles.

Other recent research found a rate as low as 1 in 1,700 in children in Germany infected with measles before age 5.

The new research results emphasize the importance of herd immunity by vaccination, the researchers said. That means that having a high proportion of the population immunized against a disease will provide greater protection to those who are not able to be vaccinated.

Infants under the age of 12 months are too young to receive the measles, mumps, and rubella (MMR) vaccine.

“We need to get everyone vaccinated on time to protect infants and those who are immunocompromised,” Dr. James Cherry, M.Sc., an author of the study, and a distinguished research professor of pediatrics and infectious diseases at the David Geffen School of Medicine at UCLA, told Healthline.

Read more: Measles vaccine has saved 17 million lives since 2000 »

Measles in the brain

For most people who get measles, the symptoms are fever, cough, runny nose, red eyes, sore throat, and a rash that is gone within 14 days.

In rare cases, the measles virus spreads to the brain, where it remains dormant for four to eight years.

Eventually, it can lead to SSPE, which involves progressive neurological symptoms.

Symptoms can start with personality changes and declining school performance, and progress to convulsive and motor disorders, and later hypothalamic dysfunction and diminishing cortical activity.

Death typically occurs within one to three years of diagnosis.

Getting measles during pregnancy can cause early labor, miscarriage, and having an infant with a low birth weight.

Measles in people with AIDS or weak immune systems can be severe.

Read more: Rise in measles, whooping cough being driven by unvaccinated people »

Measles is highly contagious

According to the , infected people can spread measles to others up to four days before they get a rash, and until four days after it appears.

It’s spread by coughing and sneezing and can live for up to two hours in an airspace where an infected person coughed or sneezed.

People can become infected by breathing contaminated air or touching an infected surface and then touching their eyes, noses, or mouths.

Ninety percent of people not immune to measles who are close to someone who has measles will also become infected, the CDC says.

Read more: Children with HIV often lack measles immunity »

California connection

In the current study, researchers identified 17 confirmed cases of SSPE that occurred in California between 1998 and 2015.

Eight of the patients were born in the United States.

A dozen had a history of measles or a measles-like illness at less than 15 months of age and were all unvaccinated because of their age.

Most of them were thought to have been exposed in the United States. Additionally, most of them were vaccinated on time, but after measles infection.

Cherry didn’t think there was anything unusual about the rate of SSPE in California.

However, he noted that there are things about SSPE that we don’t yet understand, and co-factors that are thought to make it more likely.

Males are more likely to contract it than females.

“It’s more common in rural than urban areas,” he said. “No one knows why.”

Read more: Measles cluster in California due to unvaccinated children »

Vaccination timetable

Previous research has shown that immunization reduced SSPE incidence by greater than 90 percent.

No cases of SSPE have been associated with vaccine-strain virus.

“The idea that nature is best is wrong for vaccinations,” Cherry said.

He emphasized the importance of having children get the first dose of the MMR vaccine at 12 months.

A second dose should be given at least 28 days later in children, as well as in adults who have not had measles or been vaccinated, according to the CDC.

Cherry does not recommend spreading out or delaying vaccinations.

“It’s absolutely the worst thing to do,” he said.

Read more: Understanding opposition to vaccines »

Infectious countries

In places like Asia and western Europe, measles is more common than in the United States, and vaccination rates are lower.

“If it’s up to me, I say don’t go to high risk areas in Asia and western Europe until your child is old enough for two doses of vaccine,” Cherry said.

He said if someone was moving there that would be different, but otherwise he recommends delaying travel.

A new California vaccination law went into effect on July 1 and removed some vaccine exemptions.

This means that more children are required to have completed vaccination before attending school.

Cherry is hopeful this will increase vaccination rates and decrease SSPE rates and other diseases preventable by vaccines.