Some people think of measles as a simple childhood illness that causes an itchy rash. But measles is a very contagious disease that can result in some serious complications.

A total of 1,250 individual cases of measles have been confirmed so far in 2019, according to the Centers for Disease Control and Prevention (CDC). According to the CDC, this is the greatest number of cases reported in the U.S. since 1992, when 963 cases were reported for the entire year. Cases have been reported in 31 states this year so far.

More than 75% of the cases this year are linked to outbreaks in New York. There were 649 confirmed cases in New York City alone from September 2018 through August 2019. At one point, health officials declared a state of emergency in Washington earlier this summer. In 2019, the state had two outbreaks of measles, with a total of 86 cases. The second outbreak ended in August.

The U.S. declared that measles were eliminated in 2000. The CDC defines measles elimination as "the absence of continuous disease transmission for 12 months or more in a specific geographic area." The New York outbreak had put the U.S. at risk of losing its eliminated status for measles. But when the outbreak ended in October, the U.S. Department of Health & Human Services said that measles is still considered eliminated in the U.S.

But measles isn't just a problem in the U.S. The World Health Organization (WHO) reports that there have been more than 364,000 measles cases reported in 182 countries in the first six months of 2019. Reported measles cases are the highest they have been in any year since 2006.

(Measles is also called rubeola, so it's worth noting a common misunderstanding: Rubeola and rubella — though spelled similarly — are not the same disease. As the Mayo Clinic explains, they are caused by different viruses and both involve a rash, but that's where the similarity ends.)

Here's what to know about measles, which has been in the headlines so much lately.

How do people get measles?

Measles is caused by a virus that lurks in the system of an infected adult or child. When they cough, sneeze or even talk, they spread droplets of the virus into the air around them. Other people either inhale those droplets or pick them up from a surface where they landed. Those virus droplets can remain alive and well for hours, reports the Mayo Clinic. About 90% of susceptible people who are exposed to an infected person will become infected with measles.

And someone may be spreading measles before they even know they are sick. For the first 10 to 14 days after you're infected, the virus incubates, meaning you have no signs of the illness.

measles rash on child's chest The measles rash can start as flat, red spots and later become raised bumps. (Photo: phichet chaiyabin/Shutterstock)

What are the symptoms of measles?

About 10 days or so after you're exposed to the virus, you might notice a high fever, a cough, runny nose and red, watery eyes. Two or three days after symptoms start, you'll likely notice tiny white spots inside your mouth. A few days later, an irritating rash will spread across your body, usually beginning on your face and hairline and spreading to your neck, torso, arms, legs and feet. It can start as flat, red spots and later become raised bumps. Symptoms usually last just a few days, but it could take a few weeks for you to recover from fatigue.

What happens if symptoms get worse?

Children under 5 and adults over 20 are more likely to develop complications from measles. One out of every 20 children with measles will get pneumonia (the most common cause of measles-related death) and one out of every 1,000 will develop encephalitis or swelling on the brain, according to the CDC. Other possible complications include ear infections, severe diarrhea, bronchitis, laryngitis and croup.

What long-lasting effects does measles have on the body?

New studies have found that measles can seriously weaken your immune system for years, leaving you vulnerable to diseases that you were once protected against. A pair of studies in Science and Science Immunology finds that measles can trigger "immune amnesia," meaning that your body loses antibodies that had protected it from other infections like the flu, pneumonia or chicken pox.

“Imagine that your immunity against pathogens is like carrying around a book of photographs of criminals, and someone punched a bunch of holes in it,” said Michael Mina, one of the study's primary authors, in a Harvard Medical School press release. “It would then be much harder to recognize that criminal if you saw them, especially if the holes are punched over important features for recognition, like the eyes or mouth."

The researchers suggest that after a measles infection, doctors might want to strengthen a patient's immune system by offering booster shots for routine vaccines like hepatitis and polio.

How is measles treated?

There's no specific treatment for measles, so your best bet is to try to ease your symptoms. Get plenty of rest and drink lots of fluids. Take an over-the-counter medicine like acetaminophen or ibuprofen to reduce a fever. Never give aspirin to a child or teenager with flu-like symptoms because aspirin has been linked to the rare but life-threatening Reye's syndrome.

little girl getting vaccinated Getting two doses of the vaccine is about 97% effective at preventing measles. (Photo: Tatevosian Yana/Shutterstock)

How effective is the measles vaccine?

The measles vaccine is very effective, according to the CDC. One dose of the vaccine is about 93% effective at preventing measles if you are exposed to the virus and two doses are about 97% effective.

Only about three out of 100 people who have had two doses of the vaccine will get measles if exposed to the virus. Why do some people get measles even after getting vaccinated? Experts think maybe their immune systems didn't react like they should have to the vaccine. But fully vaccinated people will have milder symptoms and are less likely to spread the disease to other people.

There's a lot of discussion now about whether middle-aged and older adults might need to be revaccinated. According to the CDC, if you received a live measles vaccine in the 1960s, you should be protected. If you were vaccinated before 1968 with inactivated (killed) measles vaccine or if you don't know what type of vaccine you received, you should be revaccinated with at least one dose of the live measles vaccine. If you're unsure, there's no harm in getting another dose of the vaccine.

What happened before the measles vaccine?

Health care providers in the U.S. didn't start reporting measles cases until 1912, according to the CDC. When they did, there was an average of about 6,000 measles-related deaths each year. In the decade before the measles vaccine was made available to the public in 1963, almost all kids got the measles by the time they were 15. There were about 3 to 4 million cases each year with an estimated 48,000 hospitalizations and 400 to 500 deaths.

What impact did the vaccine have?

In 1968, an improved, weaker measles vaccine was distributed and this is the one still in use. The measles vaccine is usually combined with mumps and rubella (called MMR), or with mumps, rubella and varicella (MMRV). By 1981, measles cases had dropped to 80% fewer than the year before. Measles outbreaks in 1989 among schoolchildren who had been vaccinated prompted many medical groups, including the American Academy of Pediatrics, the American Academy of Family Physicians and the Advisory Committee on Immunization Practices, to recommend a second dose of MMR vaccine for all children.

In 2000, measles was declared eliminated in the U.S., meaning there was no continuous disease transmission for more than 12 months, reports the CDC.

If measles has been eliminated, where did these cases come from?

Even if a disease is considered eradicated from an area, it doesn't mean it will never appear there again. Travelers can bring it back when visiting other countries where the illness thrives, and that's what is believed to have happened with measles outbreaks. Then, once the virus enters the U.S. it is spread, particularly in communities where there are large numbers of unvaccinated people, according to the CDC.

vials of medicine When most of the community is vaccinated, that offers protection to everyone else with a concept known as 'herd immunity.' (Photo: itsmejust/Shutterstock)

How many people skip the measles vaccine?

According to the CDC, 91.5% of children got the MMR vaccine in 2017, the latest year for which statistics are available. That's almost enough for "herd immunity" or "community immunity," which means that enough people in a community are protected to keep germs from spreading and getting other people sick. To get herd immunity from measles, about 93 to 95% of people need to be vaccinated, reports WebMD.

"The whole principle is if you give a vaccine to somebody, you protect them from getting infected, but you also prevent them from transmitting the disease to other people," Michael Brady, M.D., associate medical director at Nationwide Children's Hospital in Columbus, Ohio, and a member of the hospital's Division of Infectious Diseases, tells WebMD.

In the case of measles, there are places throughout the country where vaccine refusal rates are exceptionally high. All 50 states require certain vaccines for students, but all school laws grant exemptions for medical reasons and almost all states grant exemptions for people who are against vaccines for religious reasons, according to the National Conference of State Legislatures. In addition, 15 states allow exemptions for people who object to vaccines for personal or moral beliefs. Only California, Mississippi, West Virginia, New York and Maine do not allow religious or personal-belief exemptions.

The measles vaccine does not cause autism

The myth that the vaccine causes autism stems from a 1998 study by Andrew Wakefield, published in the medical journal The Lancet. The paper was retracted in 2010 with the editors of the journal telling the Guardian, "It was utterly clear, without any ambiguity at all, that the statements in the paper were utterly false.”

The gastroenterologist lost his medical license, as he was found to have acted "dishonestly and irresponsibly” and no further studies were able to reproduce his results that found a link between autism and vaccines.

Most recently, a 2019 study of more than 650,000 children in Denmark found that the MMR vaccine doesn't increase the risk for autism or trigger autism in kids who are at risk. The study was published Monday in the journal Annals of Internal Medicine.

Researchers followed 657,461 children (born between 1999 and 2000) through August 2013. They documented diagnoses of autism spectrum disorder as well as any risk factors for autism, such as age of parents, low birth weight and sibling history of autism. More than 95% of the children received the MMR vaccine, and 6,517 were diagnosed with autism. They found no correlation between the vaccine and the diagnosis.

"At this point, you've had 17 previous studies done in seven countries, three different continents, involving hundreds of thousands of children," Dr. Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia, told CNN. He was not involved in the new study. "I think it's fair to say a truth has emerged."

Editor's note: This article has been updated with new information since it was originally published in January 2019.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

What you need to know about measles
Measles can weaken the immune system for years afterward.