2019 started with some of the worst measles outbreaks to occur in the US in decades.

It has many parents asking questions:

What happened?

Do I need to worry about my child getting measles?

Routine vaccinations for measles began in 1963 in the US. The practice was so effective that by 2000 the Centers for Disease Control and Prevention considered measles eliminated—meaning the disease was exceptionally rare.

Before the vaccination was common, 3 to 4 million people were infected with measles each year, leading to thousands of hospitalizations and hundreds of deaths.

Since 2000, cases numbered between 37 and 220 each year—until 2014, when 667 cases were reported. Measles cases have numbered in the hundreds nearly every year since. So far in 2019, more than 100 cases have been reported.

Outbreaks in early 2019 have mostly affected the Pacific Northwest. The majority of people diagnosed with measles are children under age 10 and nearly all of them were not vaccinated.

Pediatrician Dr. Pamela Phillips answers common questions about how the disease is spread and how you can prevent it.

The initial symptoms of measles are similar to those of many cold and flu-like illnesses:

• Fever
• Cough, usually dry
• Runny nose
• Red, swollen eyes (conjunctivitis)
• Flat, red, spotty rash that starts 4-5 days after other symptoms
• Koplik's spots—white spots inside the mouth

"The hallmark of measles is still having fever while they have a rash," Dr. Phillips says. "With most illnesses, the fever breaks and then you might have a rash. With measles, the rash comes in the middle of the illness instead of after."

The illness can be very severe and result in potentially deadly complications, including pneumonia and encephalitis—swelling of the brain.

The measles virus is among the most highly contagious known viruses. If someone with measles coughs or sneezes, the droplets in the air or on surfaces can infect people even hours later.

Once the virus is breathed in, it attacks the immune cells protecting the lungs. Then it rides through the body on immune cells and travels to the trachea, or windpipe.

Instead of coming from deep inside the lungs, the viruses spring from just a few inches away from your nose and mouth—so a single cough or sneeze packs a high concentration of viruses, making the measles unusually easy to spread to anyone who isn't immune.

"You could be in an elevator where someone with measles was 2 hours before and you could still get it if you're not vaccinated or if you never had measles before," Dr. Phillips says.

"You might never be in the same room as the person who was infected. You just need to be in the same airspace."

You can prevent measles.

"Vaccination works," Dr. Phillips says.

93% of people are immune to measles after 1 dose of the MMR vaccine, a combination vaccine for the measles, mumps, and rubella. 97% are immune after 2 doses.

The first dose of the vaccine is typically given to children when they turn 1. A second dose is given at age 4. The additional dose was added when there were measles outbreaks in older kids in the 80s and 90s.

"We need to be vaccinated not just to protect ourselves and our own kids, but also to protect vulnerable populations, like babies under 12 months old and people receiving chemotherapy," Dr. Philips says. "That's why it's such a public health issue."

What if you have a baby who hasn't been vaccinated or a loved one with a compromised immune system? What if you're traveling to an area where there's an outbreak?

Dr. Phillips has a few additional suggestions:

• The MMR vaccine can be given safely as early as 6 months old, Dr. Phillips says. It won't count toward their school requirements and it may not be covered by insurance. If you're travelling to Europe or developing countries with an infant, consult your doctor about whether you should vaccinate your baby early, she says.
• If you have an infant, only welcome visitors who are vaccinated. "Nobody who is unvaccinated should come over, ever," Dr. Phillips says.
• The risk of catching measles—or any illness—is always higher in crowded, high-traffic places like airports, malls, and tourist attractions.

One thing you don't need to worry about is the safety of the MMR vaccine.

"The fear of this vaccination all started years ago with a fraudulent study that has been retracted—it's all based on misinformation," Dr. Phillips says.

This fear resulted in further studies of vaccines, especially the MMR vaccine.

"The only good thing to come out of it is that if we didn't know before that our vaccines are safe, we definitely know it now," she says. "In just the first decade of giving the vaccine, millions of lives were saved."