Before vaccines, nearly every child in the United States caught the virus. Today, however, public health experts emphasize that while natural immunity does occur after infection, the risks of measles are far too high when compared to the protection offered by the measles, mumps and rubella (MMR) vaccine.

Early 2025 data show rising cases in the U.S., a reminder that measles still spreads quickly wherever vaccination rates dip.

Natural immunity and the role of vaccines

“Natural immunity is wonderful. It's part of the evolution of the human body that has taken all our exposures and creates a memory for them, so that we can protect ourselves in the future. Vaccines augment (improve) that. There are some infections that an individual doesn't have to go through, or are so severe to go through, that receiving a vaccine is more valuable,” says Doug Kasper, MD, infectious disease specialist with OSF HealthCare.

He notes that measles is one of those infections.

“Measles is highly infective and has potential complications in our child population. The key with measles is that the vaccine is so effective at preventing infection. It's unanimously beneficial to receive and has been that way for a long time in the United States.”

For older generations who remember having measles as kids, it can be easy to assume it wasn’t serious. But modern evidence paints a different picture: measles can lead to pneumonia, hospitalization, brain inflammation, long-term complications and death – even in healthy children.

Why measles vaccination remains essential for kids

“Fortunately, measles vaccination remains part of the normal pediatric vaccine schedule. It's something that would be discussed with the parent regarding their child at a standard visit,” Dr. Kasper says. “We strongly recommend all children receive all their childhood vaccinations, which includes the measles, mumps and rubella (MMR) vaccine. The timing of that vaccine begins at one year of age, but it can sometimes be given earlier if there is a local outbreak of measles in the community.”

MMR vaccination rates need to remain extremely high, typically above 95%, to prevent outbreaks. However, declining vaccination rates across parts of the Americas have caused concern. The Pan American Health Organization recently warned that the region may lose its measles elimination status without urgent action.

Vaccines build a “library” of protection

The goal of vaccination isn’t to replace the body’s defenses – it’s to strengthen them.

“In the hospital, we tend to see people that get sicker, so that's what we focus our efforts on. But a lot of medicine is done outside of the hospital, and that is preventive medicine,” Dr. Kasper says. “So, the strategy with vaccine is to try not to get sick or try to get less sick than you would've. Use the utility of the vaccine, along with natural immunity, to build up your individual reservoir as much as possible to protect you in the future.”

This “reservoir” or “library” of immunity is especially important with a virus as contagious as measles, which can linger in the air for hours and infect up to 90% of unprotected people who are exposed.

Localized outbreaks are driving current cases

While measles is not widespread across the U.S., localized outbreaks continue to occur in communities where vaccination rates have dropped. Public health departments monitor these cases closely and respond with tools such as:

• Rapid case investigations
• Community education
• Mobile vaccination units
• Early MMR vaccination for children who qualify

Without high vaccination coverage, these small outbreaks can grow quickly. That’s why maintaining strong MMR rates is essential – to protect children, prevent community spread and preserve decades of progress toward measles elimination.

For more information on measles symptoms and long-term risks, visit the OSF Newsroom.

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The third week of March marked a regrettable milestone. The number of measles cases soared past the number in all of 2024. Dana DeShon, APRN for Peoria, Illinois-based OSF HealthCare, says globally the mortality rate of children worldwide has been reduce by 51% by just the act of vaccinating them. Vaccines save more than 4-5 million lives each year and have prevented approximately 50 million deaths between 2000-2019.

However, DeShon worries that in the United States, vaccine hesitancy will bring measles back as a public health crisis. The advanced practice registered nurse has been involved with the United Nations Foundation initiative called Shot@Life through which she and others lobby Congress to fund vaccine support for children in low-income countries.  According to Deshon, the funding accounts for less than 1% of the total U.S budget but saves 2.5 million lives every year worldwide.

However, these days, she’s focused on vaccinations at home.

DeShon says most of the population hasn’t seen the devastating impact of the highly contagious measles because it was eradicated in 2000. But measles is making a resurgence because of vaccine hesitancy. And measles is the most contagious of all vaccine-preventable diseases.

It begins with a runny nose, watery eyes and then a rash so people can be walking around, spreading the airborne virus before severe symptoms develop.

“You’re contagious four days before that rash and up to four days after so we could have 8 to 10 days of people walking around not even knowing they have measles and then they’re just spreading it around to people at risk. Obviously, the people most at risk, are the people who are not vaccinated,” DeShon points out.

That includes babies who can’t be vaccinated until age 1, along with pregnant women and immunocompromised cancer patients who can’t get vaccinated.

Vaccine hesitancy was fueled in the 1990s by a bad study from a physician who has since lost his license to practice medicine. The research, published in a respected medical journal, The Lancet, involved only 12 patients and falsely linked vaccines with autism. DeShon said the study has been retracted and there is, in fact, NO scientific evidence that vaccines cause autism.

She emphasizes the National Institutes of Health (NIH) spent millions on research.

“Outside research was also done and there were no links that they could find from that original Lancet study. It got to the point that they said, ‘We’re not going to do anymore studies because they did not see a link between autism and the MMR (measles, mumps and rubella) vaccine.”

Measles vaccination rates are falling

The Kaiser Family Foundation says measles vaccination rates in most U.S. states have fallen below the 95% threshold scientists consider necessary for so called ‘herd immunity’ to control the disease, and those rates have continued to drop. That’s concerning for DeShon.

“How are we going to stop this? It is not vitamin A. Vitamin A is not going to stop the measles outbreak. We need vaccinations. That is what is going to stop the outbreak that we are seeing, not just in west Texas, but all over in these pockets we’re seeing in the United States right now.”

DeShon stresses when the population is vaccinated, measles goes away. Receiving one and two doses of measles vaccine is 93% and 97% effective, respectively, in preventing measles.

She points to an outbreak at a Chicago migrant shelter last year. Fifty-seven measles cases were associated with people in the shelter. Most cases occurred in people who were unvaccinated. A prompt and coordinated response with a mass vaccination campaign reduced the size and duration of the outbreak and stopped what might have become a statewide public health concern.

The Centers for Disease Control and Prevention (CDC) says measles can lead to severe complications, including pneumonia, encephalitis (inflammation of the brain), and in some cases, death. Children, especially those younger than 5 years old, are at a higher risk of developing serious complications from measles.

A school-age child in Texas died from the measles and the New Mexico Department of Health is reporting the death of an unvaccinated adult who tested positive for measles. Even if a child survives measles, it can have long-lasting effects.

A condition called subacute sclerosing panencephalitis, or SSPE, a degenerative neurological condition can develop seven to 10 years after a measles infection, according to DeShon. 

The disease carries a heavy toll. So DeShon reminds everyone that while vaccination is a personal decision, it impacts health systems, communities, and the most vulnerable among us.

“When it comes to the point that this is something that is so contagious, and now deadly, then we really need to stop and think, ‘We need to be doing this, not because of me but because of those around me.’”

If you’re unsure whether you have immunity against measles, talk to your health care provider about your options.

OSF pediatric nurse practitioner Dana DeShon

Measles can spread through respiratory droplets (like when you cough and sneeze), and it only takes a small amount of the virus to cause infection in others. 

"It can remain in an area for an hour or two after the infected person has left the area. The difference: in a setting that you have many people in a convalescent center, social center or shelter, you'd be concerned about exposure to the unvaccinated people," says Doug Kasper, MD, an infectious disease specialist with OSF HealthCare. 

The World Health Organization (WHO) calls measles a "serious airborne disease,” reporting 107,500 measles deaths globally in 2023. Most deaths were in children under the age of five. The WHO partially blames the COVID-19 pandemic for the reemergence of measles globally, saying immunization rates and surveillance declined because of it. In 2023, 10.3 million measles cases were reported worldwide, a 20% increase from 2022. 

In 2024, the Centers for Disease Control and Prevention (CDC) reports 280 measles cases have been reported in the United States from 32 jurisdictions, including Washington D.C.

Sixteen outbreaks have been reported this year, compared to four in 2023. Outbreaks are when there are three or more related cases. The CDC adds that 40% of the reported 280 cases ended up in the people being hospitalized.

Who is most at risk?

"The particular populations that we are most concerned about if they were to become exposed to measles are pregnant women or children under the age of five. They can have more severe clinical outcomes," Dr. Kasper says. “We are not seeing any concern for measles in Central Illinois. There has been sporadic reporting of cases by the Illinois Department of Public Health out of Chicago. But the unique details of those cases have not been shared so far. Where did the people travel from? Had they been previously vaccinated? Or were there exposures in the household? We await some guidance if there is a unifying feature among them.”

Measles outbreaks in Illinois

This fall, the Pan American Health Organization, the WHO'S branch in the Americas Region, issued an epidemiological alert for measles cases in the Americas, with the U.S. accounting for the most cases. 

Illinois and Minnesota have reported the most measles cases in the U.S. this year. 

In March, the Chicago Department of Public Health (CDPH) reported a measles outbreak in a migrant shelter in the city's Pilsen neighborhood, located in the Lower West Side. The CDPH considered the outbreak "contained" in late May, crediting a rapid vaccination response. 

Vaccine mitigation

One dose of the measles, mumps and rubella (MMR) vaccine is 93% effective, while two doses jump to 97% effective. If you've been vaccinated against measles, you're unlikely to have any symptoms at all. The measles vaccine is given alone or often combined with vaccines for mumps, rubella and/or varicella.

"Fortunately, we have widespread vaccination as a standard part of medical care in the United States. As children we receive two shots of the measles, mumps and rubella (MMR) vaccine starting at age one. The second shot will be before entering school at age four or five. The vaccine is highly effective at preventing measles. So, while measles is highly infectious, we have a nationwide response to prevent outbreaks of infection,” Dr. Kasper says.

The recommendation is to complete your childhood vaccine series, which Dr. Kasper calls "very safe, durable and long-lasting." 

Measles symptoms

Symptoms for unvaccinated people: 

• Upper respiratory infections (resulting in a cough or runny nose)
• Followed by fever or rash – fever can be very high (103-104 degrees) 
• Blue spots in the mouth or along the gumline (seen a week into infection)
• Red and watery eyes
• Small white spots inside the cheeks  
• Illness can lead to meningitis or encephalitis

Because of the potential lead to meningitis or encephalitis, Dr. Kasper says getting vaccine protection is the definitive recommended option instead of developing natural immunity. He adds neurological effects down the road are also a concern. 

If families with children under one year of age plan to travel outside the country or to a large metropolitan area in the U.S. with low or no measles vaccination rates, parents should speak to their child's pediatrician. The child's doctor may recommend starting the measles vaccinations as early as 6 months of age. Currently, Dr. Kasper says there is no concern for widespread measles activity in schools, senior living communities or the general public. 

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