How dangerous is a measles outbreak?

MMR vaccine

Measles may not be an everyday concern in the United States, but it’s still a very contagious and dangerous disease. The disease was largely eradicated in this country after the measles, mumps and rubella (MMR) vaccine was approved for use in 1963.

However, the first case of measles in a Chicago resident since 2019 was recently confirmed and serves as a reminder that the disease can still strike at any time, especially in areas with low vaccination rates.

As a pediatric infectious diseases specialist, I want to share some information about measles, and why this preventable disease is suddenly in the news again.

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

Measles is an infection caused by a virus. Symptoms include fever, cough, runny nose, rash and red eyes ("pink eye" or conjunctivitis). The virus can cause additional complications such as ear infections, pneumonia and diarrhea.

A serious complication 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 primary measles infection, with the highest rates seen in children infected before 2 years of age.

How contagious is the 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 (less common). For persons who are unimmunized and have never been exposed to the virus, the likelihood of contracting measles is 90% in close-contact settings. Patients with measles infection are contagious from four days before the rash through four days after the rash appears.

People typically develop symptoms such as fever, runny nose, red and watery eyes and a cough eight to 12 days after their initial exposure to the virus. The characteristic measles rash appears three to five days after the first symptoms.

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

Greater than 99% of people who receive two doses (with the first dose administered on or after 12 months of age) of MMR vaccine, per U.S. Centers for Disease Control and Prevention (CDC) recommendations, develop immunity to measles. Given the effectiveness of the vaccine, measles circulates at much lower rates in the community and the disease is much less common than it used to be. Before the measles vaccination program began in the 1960s in the U.S., there were 3 million to 4 million cases of measles and 400 to 500 resulting deaths every year. In 2023, there were 58 reported measles cases, compared to 121 reported measles cases in 2022.

While it is possible to contract measles after two doses of the vaccine, it is very uncommon. As with many other viral vaccines, those who contract the virus while vaccinated seem to have more mild symptoms and are less likely to spread the virus to others.

Why is it making a comeback now?

Thanks to the success of immunization, measles is no longer endemic in the U.S. Measles is generally imported globally, and infection spreads locally among un- and under-immunized people. Recently, misinformation about vaccines and their risks has led to reduced rates of vaccination in some communities, making them especially vulnerable to outbreaks.

How dangerous is measles?

Fortunately, for most people, it's a minor illness — but the problem is that you can't predict who will become seriously ill. Three in 1,000 children who contract measles will die; however, if everyone is vaccinated, no children will die. Before the vaccine, there were up to 500 U.S. deaths a year from measles, and now it's completely preventable. For those vulnerable due to preexisting conditions that impact their immune system, measles can be even more dangerous. With vaccine-preventable illnesses, most people don't get sick. You might not get in a car accident every time you drive, but that doesn’t mean you shouldn’t protect yourself with a seat belt when you do. Why take the risk when the protection is safe and effective?

When should children get vaccinated? How often or how many times?

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

Would it be a cause for alarm if there were a case of measles in my local community?

It would be concerning. However, certain groups should be more concerned and some environments would be riskier than others. For example, say a patient with measles arrived in the Emergency Department (ED). The illness would have to be quickly identified and the patient placed in appropriate isolation to keep the virus from spreading rapidly since many patients coming to the ED are unwell.

It also matters how the person became infected and their population. If you happen to be a member of a community with a large number of under-vaccinated people, the risk is potentially very worrisome. The number of people who get sick when exposed to measles is very high if they're not vaccinated. The overall vaccination numbers in a city may be robust, but an outbreak can still spread within certain pockets where not enough people are vaccinated.

What should I do if I’m exposed 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.
  • Call your healthcare provider right away if you are exposed.

Your healthcare provider can work with you to 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. Ask your provider about your options. 

If you and/or your child are fully vaccinated (two doses of MMR vaccine), you should 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 the doctor’s office without calling ahead to ensure that you do not put other patients at risk.

Julia Rosebush

Julia Rosebush, DO, FAAP

Julia Rosebush, DO, FAAP, serves as UChicago's Medical Director for the Care2Prevent Pediatric/Adolescent HIV Program and Director for the Pediatric Infectious Diseases Fellowship Training Program.

Learn more about Dr. Rosebush

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