While infection does contribute to the immune “library,” modern vaccines offer a safer, more reliable way to add to that protection without the risks of serious illness, hospitalization or long-term complications.

As flu activity increases across the U.S. this winter, experts emphasize that vaccines remain one of the strongest tools for maintaining health and preserving natural immunity over a lifetime.

Vaccine decisions start with informed conversations

“Vaccination is an individual decision, but the impact of the vaccine protects both the individual and their family cohort, work cohort. If they're in school, it can protect that community,” says Doug Kasper, MD, infectious disease specialist with OSF HealthCare. “We want people to be as educated as possible and make the best decision for themself. That's really going to come down to a discussion with them and their medical provider.”

For older generations who remember “just getting the measles,” today’s medical guidance recognizes that while infection can create immunity, it also carries significant risks – and vaccines provide a much safer pathway to the same immune protection.

How flu vaccines strengthen natural immunity

“Flu vaccines, historically, never match up perfectly to all the influenza strains that circulate in the community. What we do know is that immunity is cumulative; it's a library across a person's life and it has all of their prior infections and vaccines. It builds up over time,” Dr. Kasper says.

He explains that vaccines support and expand your natural immune memory.

“Receiving a seasonal flu vaccine, while the protection it may provide in any year may be different; over time there are benefits to doing this activity, so that you have a robust variety of immunity. As the seasonal infections change, you may be protected from something that happened in the past.”

This means vaccines don't replace natural immunity – they contribute to it, adding layers of defense that reduce the severity of illness and strengthen long-term protection.

Why vaccines remain a powerful community tool

Vaccines benefit individuals, but they also help stabilize the entire health system.

“When we talk about vaccination, we talk about it at a population level. We would like every individual to not get sick, but we also know that with hospitals, urgent cares and emergency departments, that we are trying to keep the system functional,” Dr. Kasper says. “We do that by getting as few people sick as possible, and vaccines are a very useful tool to help the individual help their community and help the medical system.”

A season of multiple circulating viruses

As families enter the stretch leading up to Christmas, flu activity is increasing on both coasts – often a preview of what will soon reach the Midwest.

COVID-19 continues to circulate year-round, RSV season is underway and Central Illinois is just beginning to see early influenza activity. Early surveillance suggests this year’s flu vaccine may not be a perfect match, but even imperfect vaccines help reduce severity, hospitalizations and complications. They also continue contributing to the “immune library” that protects people long-term.

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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

There’s a misperception that measles is a thing of the past.

Not so.

Measles was declared eliminated in the United States in 2000 but is seeing a resurgence in 2024. As of March 22, there have been 64 cases across the U.S. – compared with 58 in all of 2023. The cases have appeared in at least 17 states so far, including Illinois and Michigan.

The cause of the increase is two-fold – the number of people who are unvaccinated has increased and the rise in international travel to destinations such as Britain, Austria and the Philippines, where outbreaks have occurred.

According to Alissa Bartel, a nurse practitioner with OSF HealthCare, there’s no reason to be concerned yet. “I think it's always good for parents to be aware, be educated and not alarmed, but know that it is possible, especially in those kids who are at highest risk,” she says.

Measles is a highly contagious disease caused by a virus. It spreads when an infected person breathes, coughs or sneezes. That person can spread measles to others even before knowing they have the disease — from four days before developing the measles rash through four days afterward.

Symptoms include a high fever, cough, runny nose and a rash that starts at the top of the head and travels down the trunk to the lower extremities. Complications can lead to pneumonia, swelling of the brain and even death.

Measles can affect anyone but is most common in children.

“The most vulnerable of developing measles would be those who are not vaccinated; so kids under 5 years old or any child who has not chosen to be vaccinated, also those who are receiving chemotherapy or any medications that might make them immunocompromised,” says Bartel. “Also, pregnant women are very high risk, not only for themselves if they haven't been vaccinated, but also for the child that they're carrying.”

The best way to prevent getting sick with the measles and spreading it to others is from the measles-mumps-rubella (MMR) vaccine.

“We’ve had so many vaccines that have helped us to drive so many serious illnesses and diseases away,” says Bartel. “However, we are seeing a lot of them emerge again. It’s important for us to educate our patients on vaccines, not only for ourselves, but to protect others who can't receive vaccines.”

The Centers for Disease Control and Prevention (CDC) recommend children get their first MMR dose between the ages of 12-15 months. The second dose is between ages 4-6. Teenagers and adults require only one dose and should get it as soon as possible.

According to the CDC, two doses of MMR vaccine are about 97% effective at preventing measles, and one dose is roughly 93% effective.

For parents experiencing vaccination hesitancy, Bartel recommends having a conversation with your family physician. Experts stress it’s important to eliminate potential barriers such as cost. Children can be vaccinated for free through private insurance or the Vaccines for Children Program, a federally funded, state administered program that provides free vaccines to eligible children ages 18 and younger. 

Some parents may not realize the potential seriousness of their young ones contracting measles. The World Health Organization reports that the measles vaccination prevented 56 million deaths between 2000 and 2021. An estimated 128,000 people died from measles in 2021 – mostly children under the age of 5.

“Open the conversation about vaccines and vaccine hesitancy and then also know that you can trust your provider. They know what's best for your children,” she says. “They can also point you to really good resources, trusted resources. If you like to read about things and make really educated decisions, we can empower our patients to do that.”

For more information on the measles, visit OSF HealthCare. 

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