What You Need to Know About the US Measles Outbreak

Written By: Kelseanna Hollis-Hansen - PhD, MPH, UT Southwestern Medical Center, Harold C. Simmons Comprehensive Cancer Center

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US Measles Outbreak TL;DR

• Measles spreads like wildfire. In a susceptible community, each person infected with measles will give it to another 12-18 people.
• The measles vaccine is safe and effective. The measles vaccine has been approved and monitored for safety for over 60 years.
• If you are not yet vaccinated or unsure if you’ve been vaccinated, talk to your doctor about getting you or your loved ones protected and stop the spread.
• If you or a loved one does not have health insurance, there are many programs that allow you to get the vaccine for FREE. Use https://www.vaccines.gov/en/ and https://www.naccho.org/membership/lhd-directory  to locate a free or low cost vaccine today.

Why are so many people worrying about measles right now?

Measles is one of the most contagious infectious diseases and it’s currently spreading around the U.S. Nearly 500 people have been infected in 20 states as of April 2025. Experts use a number called the "Basic Reproduction Number" (R₀) to measure how easily a disease spreads. Measles has an R₀ of 12-18, meaning each person infected with measles will spread it to up to 18 others in a group of people who aren’t immune.

In 2000, vaccination rates were higher, and experts said measles was eliminated in the U.S. because no people had been found to be sick with it for over a year. Now, measles is coming back in some places more frequently because fewer people are getting vaccinated. When enough people are vaccinated or have had the disease before, it helps protect others who aren’t immune—this is called "herd immunity."

To achieve herd immunity and stop measles from spreading, at least 95 out of 100 people need to be vaccinated or have immunity from a previous infection. Currently, only 91 out of 100 children in the U.S. are protected on average, and in some areas, that number is even lower, meaning we no longer have herd immunity.

Although this recent outbreak is scary, the great news is that the measles vaccine is easy to get for free or at a low cost. The measles vaccine works by introducing a very small, very weak version of the virus to your body – it is so weak that it doesn’t make us sick. The immune system then makes what are called antibodies, which are molecules in the body that recognize and remember the virus. Antibodies help the  immune system learn to fight off the real virus if we’re ever exposed, like if a sick friend comes over for dinner or a sick classmate comes to a child’s school.

Is the measles vaccine safe?

The measles vaccine was first licensed in 1963 and improved in 1968 after a lot of testing, so we have over 60 years of proof that it is safe and works well. It’s so effective that if 100 vaccinated people are exposed to measles, only about 3 might get sick. But in a group of 100 unvaccinated people, about 10 would get sick. Unvaccinated people are not only more likely to catch measles, they also get sicker. Unvaccinated people have a higher chance of being hospitalized or even dying because measles can cause serious infections in the lungs (like bad pneumonia) and swelling in the brain.

But I’ve heard about dangerous preservatives, microchips, and chemicals in the vaccine

In the U.S., there are two measles vaccines available: MMR II and the PRIORIX vaccine. These vaccines contain no preservatives, no microchips, and no mercury or aluminum. MMR II contains tiny amounts of animal products, so some people choose PRIORIX instead, as it contains no animal products. Both vaccines are safe and effective.

Vaccines do not contain microchips. Microchips are very expensive to make, costing from hundreds of thousands to billions of dollars. Also, microchips are not designed to be submerged in liquid, and most vaccines are liquid. There is no reason to put a microchip in a vaccine. Microchips have never been in a vaccine and have never been recommended to be included in any vaccine.

The MMR vaccines do not contain aluminum or mercury. Some other vaccines do contain tiny amounts, but there’s no reason to be afraid of those vaccines either. Mercury was removed from all children’s vaccines in 2001, but it’s still in some flu vaccines.

It’s important to remember that chemicals aren’t automatically bad. Everything in the world is made up of chemicals, including humans! Chemicals are only harmful if we have too much of them. The amounts of mercury and aluminum in vaccines are so small they can't hurt us. In fact, the average American naturally consumes about 7-9 milligrams of aluminum from food, water, and air each day and is unaffected. Vaccines that include aluminum have less than 1 milligram.

What you can do to protect your loved ones and stop the spread of measles

• Talk to a doctor or pharmacist and get vaccinated. Get your loved ones vaccinated. If you or a loved one do not have health insurance, you can get the vaccine for free or low cost through the Adult Safety Net and Vaccines for Children programs. You can use these websites (https://www.vaccines.gov/en/ and https://www.naccho.org/membership/lhd-directory) to find a free or low cost vaccine provider near you today.
• Not only can you stop the spread of infection, YOU can also stop the spread of misinformation and disinformation around vaccines. Be a calm and collected voice of reason and help to stop the spread of misinformation online with what you learned in this article today or use these helpful resources created by the National Foundation for Infectious Diseases organizations.

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