Measles outbreak FAQ: Do I need a vaccine booster? What do I do if I've been exposed? And what are the symptoms?

A child has died of measles in Texas, officials said — the first death from the highly contagious disease the United States has seen in a decade.

The school-age child was not vaccinated, according to the Texas Department of State Health Services. The child’s death comes amid the state’s largest measles outbreak in nearly 30 years, which has sickened at least 146 people since late January.

Neighboring New Mexico also reported nine cases as of Tuesday, according to the state’s health department. The agency said the outbreak is happening in Lea County, across the state border line from Gaines County, Texas, where the majority of measles cases have been reported in the state.

The Centers for Disease Control and Prevention says that, as of Feb. 20, measles cases have also been reported in Alaska, California, Georgia, New York, New Jersey and Rhode Island.

Yahoo News answers some of the most frequently asked questions about the virus.

What should I know about measles?

Measles, also known as rubeola, is one of the most contagious diseases in the world, whose symptoms include fever and rash. It can lead to serious health complications, especially in children under 5 who aren’t vaccinated.

How it spreads: Through the air when an infected person breathes, coughs, sneezes or talks. It’s so contagious that nine out of 10 people exposed to the virus will get infected if they have not been vaccinated, according to the CDC.

Airborne droplets of the virus can remain in a room for two hours, even after the person with measles has left the room, according to Cleveland Clinic. Droplets of the measles virus can also land on surfaces and spread to other people that way.

Measles can also be spread by:

• Sharing food or drinks or kissing someone who has measles

• Shaking or holding hands or hugging someone with measles

• If someone touches a surface containing the virus and then touches their mouth, nose or eyes

• Pregnant women with measles can give it to their babies either during pregnancy or while nursing

Signs and symptoms: Measles symptoms can appear seven to 14 days after a person has contact with the virus. Common symptoms of measles include:

• High fever

• Tiredness

• Cough

• Runny nose

• Red or bloodshot eyes

About three days after these first symptoms start, tiny white spots might appear inside the mouth.

Three to five days after the initial symptoms begin, an infected person will develop a red, blotchy rash that often starts from the head and moves down the body. The rash can last about seven to 10 days, according to Cleveland Clinic.

People infected with measles can spread the virus to other people four days before the rash appears until four days after it goes away, the National Institute of Health says.

No treatment: There’s currently no treatment for measles and the virus has to run its course, which can take about 10 to 14 days. Overall, health agencies say the best treatment for measles is prevention through the measles vaccine.

What’s driving the latest measles outbreak?

Measles was declared eradicated in the U.S. in 2000, a feat achieved through vaccinations. Measles can be carried into the U.S. by unvaccinated travelers, including Americans, as well as foreign travelers who bring it back to the U.S. Measles can spread among unvaccinated individuals and can lead to outbreaks.

The latest outbreak in West Texas is spreading mainly through a Mennonite community.

"Measles is a great exploiter of unvaccinated individuals," Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and co-director of the Texas Children's Hospital Center for Vaccine Development, told Yahoo News. "If you have a significant population that has not been vaccinated, then measles can rip through those populations very quickly because it's one of the most highly transmissible virus agents we know."

Measles "has a reproductive number of between 12 and 18," Hotez said. "It means a single individual can, on average, infect another 12 to 18 unvaccinated individuals."

I’m an adult who was vaccinated as a child. Do I need a booster?

There are two types of vaccines that protect against measles, given in the form of a shot:

• Measles, mumps, rubella (MMR) vaccine

• Measles, mumps, rubella, varicella (MMRV) vaccine. Varicella is the chickenpox vaccine.

“MMR & MMRV vaccines usually protect people for life against measles and rubella; but immunity against mumps may decrease over time,” according to the CDC website.

However, the CDC says a certain type of inactive measles vaccine made available between 1963 and 1967 "was not effective," which is why they advise certain adults to get a booster.

"People who were vaccinated prior to 1968 with either inactivated (killed) measles vaccine or measles vaccine of unknown type should be revaccinated with at least one dose of live attenuated measles vaccine," the federal agency says on its website.

What other groups of people should be vaccinated who don’t have immunity?

The CDC recommends children get their first dose at 12 to 15 months old, with the second and final dose at 4 or 5 years old.

Hotez stresses to Americans to make sure children are vaccinated. "It was causing half a million deaths annually in the 1980s and 1970s," he says. "It was the leading killer of children globally."

The CDC says measles vaccination is especially important for adults who don’t have evidence of immunity, which include:

• Students at post-high school educational institutions

• Health care personnel

• International travelers

• People of childbearing age before they get pregnant

• Groups at increased risk for mumps because of a mumps outbreak

Regardless of age, Hotez says, "It's never too late to go ahead and vaccinate."

If you’re unable to locate your vaccination records, the Mayo Clinic recommends talking to your doctor because a blood test can confirm if you do have immunity from previously receiving a vaccine.

Dr. Céline Gounder, CBS News medical contributor, says there’s also no harm in getting a measles booster if you’re not sure. "That's actually what we would advise to do, as opposed to getting a blood test to see if there are antibodies — just get a booster if you're in doubt," she told CBS.

The CDC also advises certain people should check with their healthcare provider on whether to get vaccinated, which includes people who have a weakened immune system because of disease or medical treatments or may be pregnant.

I’ve been exposed to the measles. What should I do?

The CDC advises that if you’ve had a known measles exposure and don’t have immunity to measles by vaccination or previous infection, “talk with your doctor about getting MMR vaccine.” The health agency says it’s not harmful to get the vaccine after exposure to measles, mumps or rubella.

If you’ve had a known exposure to measles, there are two types of post-exposure prophylaxis for the virus that will "potentially provide protection or modify the clinical course of disease," according to the CDC:

• A person can get a measles vaccine within 72 hours of the initial measles exposure

• Measles immunoglobulin can be administered within 6 days of exposure

My state doesn't have a measles outbreak. Should I still be concerned?

Since measles is so contagious, doctors in states without current outbreaks are concerned about unvaccinated individuals who don’t have evidence of immunity.

"Although it is down south and far away, we do know that measles is very contagious,” Dr. Satina Wheat, a family physician at Northwestern Medicine in Chicago, told CBS News.

Just last year, Chicago had its own measles outbreak. A total of 57 migrants at a shelter tested positive for measles during March and April.

Dr. Scott Gottlieb, the former commissioner of the Food and Drug Administration, told CBS News that he believes measles will spread beyond Texas and New Mexico.

“When you have this much virus spreading in that portion of Texas and New Mexico, I think there’s some inevitability that you’re going to see cases exported into those states where there’s low vaccination rates and you could see a continuous spread across the country,” Gottlieb said. He then listed some of the states with low vaccination rates: Idaho with 80%, Alaska and Wisconsin are at about 84%, Minnesota is at 87%, while states like Florida, Colorado, Oklahoma, Georgia, Utah are around 88%.

Why are people who are vaccinated getting sick too?

The measles vaccine is safe and effective. When two doses are given, the vaccine is 97% effective against measles. One dose is about 93% effective.

In the Texas outbreak, five people who were vaccinated became infected with measles.

Few people who get two doses of the vaccine could get measles if exposed to the virus — about three in every 100, according to the CDC.

“Experts aren’t sure why,” the health agency says. “It could be that their immune systems didn’t respond as well as they should have to the vaccine. But the good news is, fully vaccinated people who get measles seem more likely to have a milder illness.”

What does it take for these outbreaks to end?

The CDC defines a measles outbreak as three or more related cases present within a specific geographic area. In order for an outbreak to end, a high percentage of eligible individuals in the affected area have to be vaccinated.

“High sustained baseline measles vaccine coverage and rapid public health response are critical for preventing and controlling measles cases and outbreaks,” according to the CDC.

Gottlieb said that for measles, “Herd immunity is achieved through a vaccination rate of about 93% and 95%.”