How dangerous is a measles outbreak?

Measles is a very contagious and dangerous disease — but it’s also preventable.

Thanks to a coordinated and highly effective effort to deliver the measles, mumps and rubella (MMR) vaccine, it was declared eliminated from the U.S. in 2000.

But increasing numbers of measles infections — driven by misinformation about vaccines and reduced vaccination rates in some communities — have been reported over the last five years.

As of mid-March 2025, there were 301 new cases of measles and 2 measles-related deaths in the U.S., surpassing the 285 cases reported for all of 2024, according to the Centers for Disease Control and Prevention.

As a pediatric infectious diseases specialist at UChicago Medicine, I want to share important facts about measles prevention that can help keep you and your loved ones safe.

What is measles — and what are the symptoms and complications?

Measles is an infection caused by a virus. Symptoms of measles include fever, cough, runny nose, rash and red eyes ("pink eye," or conjunctivitis), and they typically show up eight to 12 days after initial exposure to the virus.

The characteristic measles rash appears three to five days after the first symptoms appear. Additional complications, such as ear infections, pneumonia and diarrhea, can occur.

A serious complication of measles is acute encephalitis, or inflammation of the brain, which can result in permanent brain damage in one of every 1,000 cases. In the U.S., death from neurologic or respiratory complications of measles occurs in one to three of every 1,000 cases.

In addition, there is a late-onset complication called subacute sclerosing panencephalitis (SSPE). This rare, degenerative and fatal central nervous system disease can occur seven to 11 years after a primary measles infection, with the highest rates seen in children infected before 2 years of age.

How contagious is measles and how long is a person contagious?

Measles is one of the most highly communicable infections. It’s spread through direct contact with infectious droplets or through the air. Patients with a measles infection are contagious from four days before the rash through four days after the rash appears.

For people who are not vaccinated and have never been exposed to the virus before, the likelihood of contracting measles is 90% in close-contact settings.

How effective is the measles vaccine? Can I get the measles if I’ve been vaccinated?

More than 97% of people who receive two doses of the MMR vaccine develop immunity to measles. The second dose of the vaccine protects those who fail to respond to their primary dose.

While it is possible to contract measles after two doses of the vaccine, it is very uncommon. Importantly, immunization is not harmful to those with established measles immunity and immunized persons do not transmit measles vaccine virus.

When should children get vaccinated for measles?

Children should be vaccinated after their first birthday and receive an additional dose of MMR vaccine before entering kindergarten (when they’re 4 to 6 years old). The second dose provides additional protection to the approximately 5% of people who do not respond to their first dose.

Given the risk of measles associated with international travel, a first dose can be given as early as 6 months of age for infants who will be traveling abroad. This does not, however, replace the need for additional MMR doses administered at the traditional timepoints of over 1 year of age and 4 to 6 years of age.

Should adults get vaccinated for measles?

Adults are considered immune to measles if they have documentation of at least one dose of MMR vaccine on or after their first birthday, documentation of two doses of MMR vaccine for individuals at high risk, laboratory evidence of measles immunity, laboratory confirmation of measles infection, or birth before 1957.

Adults who do not meet these criteria should be vaccinated with at least one dose of the MMR vaccine — unless their physician recommends against it due to special circumstances, such as severely compromised immunity.

During measles outbreaks, health departments may provide additional recommendations to protect their communities, including a second dose of MMR for adults who have received only one dose previously. Currently, a third dose of MMR vaccine during measles outbreaks is not recommended.

How dangerous is measles?

Fortunately, for most people, measles is not life-threatening — but the problem is that you can't predict who will become seriously ill. Three in 1,000 people who contract measles will die. For those who are vulnerable due to preexisting conditions that impact their immune system, measles can be even more dangerous.

However, if everyone is vaccinated, no one will die. Before the vaccine, there were up to 500 U.S. deaths each year from measles, and now it's completely preventable.

With vaccine-preventable illnesses, most people don't get sick, but that doesn’t mean it’s smart to forego the vaccine. Why take the risk when the protection is safe and effective?

Should vitamin A and cod liver oil be used to prevent measles infection?

The only way to prevent measles is with the MMR vaccine. Vitamin A does not prevent measles, and in high doses, it can lead to toxic side effects such as nausea, vomiting, headache, blurred vision, liver damage and coma.

Treatment with once-daily vitamin A for two days is recommended for those with an established diagnosis of a measles infection to help the illness from becoming more severe.

Cod liver oil contains high amounts of vitamin A, vitamin D and fatty acids, which can be harmful if intake exceeds the recommended daily amount; it should not be administered to prevent measles infection.

Should I be worried if measles is found in my community?

Community outbreaks of measles should always be taken seriously. Even when overall vaccination rates are robust, outbreaks can still spread among certain populations, such as people who are immunocompromised or live in under-vaccinated areas.

Some environments also pose more risks. If a patient with measles arrives in the emergency department of a hospital, for example, the illness would have to be quickly identified and the patient placed in isolation to keep the virus from spreading rapidly to other sick individuals.

Everyone has a responsibility to take precautions to avoid the virus and to ensure their vaccinations are up-to-date to protect themselves and their neighbors.

What should I do if I’m exposed to measles or think I may have measles?

Measles is highly contagious, and you can be infectious prior to developing symptoms. Be extremely cautious in the event of a possible exposure.

• Wear a mask and isolate from others
• Contact your doctor immediately if you believe you have been exposed

Your care team can help determine if you are at risk of contracting the virus. For the unvaccinated, getting the MMR vaccine or an injection of immune globulin may reduce the risk of illness.

If you or your child are fully vaccinated (two doses of MMR vaccine), monitor for symptoms for at least 21 days and call your provider immediately if you or your child begin to experience any symptoms. Do not go into a healthcare facility without calling ahead to ensure that you do not put other patients at risk.

Where can I find additional information about measles?

• U.S. Centers for Disease Control and Prevention
• The American Academy of Pediatrics
• HealthyChildren.org