The nation is experiencing a rise in measles cases not seen in decades.
A quarter-century after the Centers for Disease Control and Prevention declared measles eradicated in the United States, the virus is back in the news.
What started out as a handful of measles cases in Texas in January has now increased to more than 1,000 nationwide — four times the number of cases logged in the entirety of 2024, according to federal health data.
Outbreaks are emerging in pockets of the country with low vaccination rates.
Health officials have reported several cases in Missouri and southern Illinois. St Louis and other parts of Missouri have vaccination rates that are below the threshold that would keep the virus from spreading. That puts communities at risk for a rapid spread if just a single person is infected.
St. Louis Public Radio’s Sarah Fentem tells us what you need to know about measles and how to protect yourself and your loved ones.
What is measles, anyway?
Measles is a viral infection caused by the rubeola virus (not to be mistaken for rubella, another viral infection, which is confusingly known as German measles).
Measles has a long incubation period: one to two weeks. Infected people first come down with a runny nose, watery eyes and a fever. Sometimes, they’ll develop white spots in their mouth. The trademark red rash starts at the hairline and works down a patient’s trunk. The rash does not usually appear until a person has been sick for days.
The virus is incredibly easy to catch and spread. Viral particles can live for hours outside the body in air and on surfaces, which is why a person can catch measles in an otherwise empty room if an infected person was there earlier in the day.
“The measles virus, unfortunately, can be very serious,” said Dr. Alex Garza, incident commander of the St. Louis Metropolitan Pandemic Task Force, which represents health officials from the region’s four major hospital systems. “This includes things like ear infections and diarrhea, but also pneumonia and swelling in the brain.”
In some circumstances, people can die of measles. The people at risk are those who haven’t been vaccinated, who are undergoing chemotherapy, who are otherwise immunocompromised or who have “really significant health conditions,” Garza said.
Why am I hearing more about measles now?
Measles is in the news because the number of cases has shot up this year, fueled mostly by clusters of outbreaks in areas with low vaccination rates. The CDC has recorded more than 1,000 cases of measles so far this year, mostly in those who are unvaccinated or whose vaccination status isn’t known.
While the rate of measles cases reported this week appears to have slowed down nationwide, the outbreak has shown how vulnerable under-vaccinated pockets are to measles’ rapid spread.
OK, that sounds bad. How can people prevent and treat measles?
The No. 1 thing people can do is get their two-dose measles, mumps and rubella (MMR) vaccine, doctors said. Unlike influenza shots and other vaccines, the MMR vaccine is extremely effective: One dose confers 93% protection against measles, and the second dose will increase it to 97%, Garza said.
The CDC recommends the first dose of MMR around a child’s first birthday, and the second around age 5.
The MMR vaccine is called a live attenuated vaccine. It contains a weakened form of the measles virus. When introduced as a vaccine, it prompts the body to make antibodies that prepare the immune system to fight the virus in the future.
A person can get a preventative immunization if they’re unvaccinated and think they’ve been exposed, but that only works for a few days after they are exposed to the virus.
If someone is unvaccinated and thinks they have been in contact with someone with the measles, they should contact their doctor about this option, called post-exposure prophylaxis.
Doctors can also administer antibody treatment to infants exposed to measles who haven’t been vaccinated.
There isn’t a specific antiviral treatment for measles, but doctors can help ease symptoms. They can also treat pneumonia and other secondary infections with antibiotics.
If I’ve gotten the vaccine, do I need a booster or another shot?
The modern MMR vaccine confers lifelong immunity to measles, said Amanda Brzozowski, senior epidemiologist at the St. Louis County Department of Public Health. If you know you’ve been vaccinated, you’re good to go.
(In contrast, the mumps component of the vaccine does wane slightly over time.)
Some older generations may have been infected with measles before it was considered eradicated. They also have lifelong immunity.
The only people who may need to consider getting another measles shot are those who were vaccinated before the mid-1960s, when the new version of the MMR vaccine rolled out.
“It wasn't a live weakened version of the vaccine, and that one is not considered as effective as the one that we use now,” Brzozowski said. “But if you were vaccinated as a kid, you do not need to get another dose.”
Bottom line: If you got a vaccine before the moon landing, give a doctor a call to ask about getting another shot. Otherwise, you’re in the clear.
Should parents consider a shot for small kids who haven’t gotten the vaccine or who have only gotten one dose?
“That is a good conversation to have with your pediatrician, because it really depends on your specific situation,” Brzozowski said.
It is safe for a small child to get an early vaccination after they are 6 months old, but that doesn’t count as part of the two-dose standard regimen (meaning the child would end up getting three doses total).
Again, the first dose of the MMR vaccine confers measles immunity to 93% of those who get it. That means even one dose is likely to be very effective at keeping a toddler or young child safe. However, if parents think a child has been exposed to the virus or is traveling to a place where measles is circulating more widely, they can talk to a pediatrician about considering an early second dose.
I heard measles was eliminated. Why is it coming back now? Could other diseases come back, too?
The CDC declared measles eliminated in the U.S. in 2000, meaning the virus wasn’t circulating in the country. (This is different from an eradicated disease, one that has been eliminated worldwide. The only human disease that fits this description is smallpox.)
However, the U.S. is seeing a resurgence of the virus in part because measles is so contagious. When vaccination rates drop below 95%, the virus can begin to spread, particularly in under-vaccinated areas.
As many learned during the coronavirus pandemic, several factors contribute to how fast a disease can spread, including how effective a vaccine is, how many people have gotten the vaccine and how contagious a virus is.
Some of those factors, such as immunizations, humans can control. But that vaccination rate has dropped in recent years.
Researchers in April published an investigation in the Journal of the American Medical Association that modeled how vaccination rates could affect the resurgence of polio, diphtheria and other diseases.
Mostly because it’s so contagious, measles was the most susceptible to those fluctuations in immunization rates, the researchers said.
How worried should St. Louisans be?
Individuals who have been vaccinated don’t need to fret much about staying safe, doctors said.
“If you are up to date on your vaccine, you were vaccinated as a kid, or you're a parent and your kids were vaccinated, you really don't need to be that worried,” Brzozowski said. “Measles is really scary. It's not just a cold, but the vaccine is excellent.”
Public health officials are worried about the trend of decreasing vaccination rates and the corresponding resurgence of a previously eliminated disease.
“Thankfully, we have a pretty high immune status in the metropolitan area against measles,” Garza said. “Now, there are certain pockets where the immune status isn't as high as we would like it to be, so I guess my recommendation would be, just be cognizant of what you're doing.”
