(NEW YORK) — Before there was a vaccine in 1963, measles infected millions and killed hundreds of people in the U.S. every year. Now, with the first measles death occurring in over a decade, doctors warn that declining vaccination rates are bringing the disease back, putting more people — especially children — at risk.

Here are five things to know about measles.

What is measles?

Measles is a highly contagious virus that can cause serious illness. One in nine people who are exposed to the measles virus will become infected if they don’t have immunity through previous infection or vaccination, according to the Centers for Disease Control and Prevention.

Symptoms often begin one to two weeks after exposure. Early symptoms can look like other common respiratory illnesses starting with a high fever, cough, runny nose, red eyes and white spots in the mouth.

Dr. Ari Brown, a pediatrician in Austin, Texas, who treated measles decades ago, warns measles “doesn’t look like measles initially, and so that’s what’s so scary … this could look like flu.”

A distinct red rash typically appears three to five days later, usually starting on the face and spreading down the body.

What is the earliest my child can get vaccinated?

The CDC recommends all children receive two doses of the MMR (measles, mumps and rubella) vaccine, with the first dose given between 12-15 months and the second dose when they reach 4-6 years old.

In some circumstances, children as young as 6 months old may receive the vaccine, and a second dose can be given as soon as 28 days after the first, according to the CDC.

Dr. Lara Johnson, a pediatrician and the chief medical officer at Covenant Children’s and Covenant Health in Lubbock, Texas, said people worried about their vaccination status should talk to their doctor.

“One of the messages that’s really important in the context of this outbreak is, if you’re behind on your vaccinations, now’s a great time to get caught up,” Johnson told ABC News.

Can you get measles if you are fully vaccinated?
One dose of the MMR vaccine is 93% effective against measles and two doses are 97% effective, according to the CDC.

That means that 3 out of 100 vaccinated people may get sick if exposed to the virus, but these infections are usually less severe than in unvaccinated people who get sick, according to the CDC.

Most people who were vaccinated as children won’t need any additional measles vaccines. But adults who only had one measles vaccination or people who were vaccinated in the 1960s may be candidates for an additional vaccination.

Anyone unsure of their vaccination status should have a discussion with their doctor. There’s no harm in getting an additional dose of the MMR vaccine. According to the CDC, people born before 1957 are immune to the virus because almost everyone at the time was infected with measles, mumps and rubella during their childhood.

Anyone living in a high-risk area should speak to their doctor about whether they need a booster, according to the CDC.

What can pregnant women do to stay safe?

Measles in pregnancy is associated with a higher risk of miscarriage, low birth weight and preterm birth, according to the American College of Obstetricians and Gynecologists. However, women should not receive the MMR vaccine while they are pregnant because it is a live vaccine.

If a pregnant person is exposed to measles, they should talk to their doctor as soon as possible — within six days — to know if they should receive a post-exposure prophylaxis with measles immunoglobulin (an injection of antibodies that can help reduce the severity of illness for high-risk people), according to the CDC.

Can measles kill you?

Measles can cause complications like pneumonia, brain swelling, long-term hearing loss and death — as is the case in the current Texas outbreak.

In the decade before the measles vaccine, the CDC estimates 3 to 4 million people were infected and 400 to 400 people died from the virus every year in the United States.

Other long-term complications include subacute sclerosing panencephalitis (SSPE), a rare but fatal complication that can develop seven to ten years after recovery. SSPE causes a gradual loss of mental abilities, which progresses to a vegetative state and eventually leads to death, according to the National Institutes of Health.

There is no specific treatment for measles, so doctors say the best way to prevent complications of measles is to get vaccinated.

“The vaccine is so effective,” Dr. Summer Davies, a pediatrician currently treating hospitalized patients at Texas Tech University Health Science Center and Covenant Children’s, told ABC News.

Davies said the best way to protect yourself, your children and your community is to get the vaccine, even “if you’re not worried yourself about getting it.”

This is not just like any other virus, Davies said.

“Some people think, ‘Oh, this is just a virus like the flu. I’ll get it, maybe get a fever and rash and get over it,’” Davies said. “But it can be really severe, as we have seen here.”

Johnson said that measles is not just an issue from the past, but something that could progress in the future without proper vaccinations.

“[Measles] seems like something from the past,” Johnson said. “But if we don’t continue to vaccinate and do things that we did in order to make these illnesses of the past, then they’ll be illnesses of the present.”

-Dr. Amanda Hargett-Granato and Jade A Cobern contributed to this report. Hargett-Granato is a pediatric resident at Mayo Clinic and member of the ABC News Medical Unit. Cobern, MD, MPH, board-certified in pediatrics and general preventive medicine, is a medical fellow of the ABC News Medical Unit.

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