If you don’t get vaccinated, you remain fully susceptible to diseases that vaccines prevent, and your body has no head start if you’re exposed. For highly contagious diseases like measles, that means a significant chance of hospitalization: about 18% of measles cases in the U.S. between 2001 and 2022 required hospital stays. Beyond your own risk, skipping vaccination also affects the people around you, particularly infants, elderly adults, and anyone with a weakened immune system who can’t fight off infections on their own.
You Face the Full Force of Preventable Diseases
Vaccines work by training your immune system to recognize a virus or bacterium before you encounter it in the wild. Without that training, your body starts from scratch when an infection hits. The difference in outcomes is measurable. In a large U.S. study of over 4,000 measles cases, people who had received two doses of the measles vaccine were about 67% less likely to be hospitalized and 61% less likely to develop complications compared to unvaccinated people. Vaccinated individuals who did catch measles tended to have milder symptoms: less fever, less rash, fewer respiratory problems.
For polio, the stakes are even starker. One in every 200 polio infections leads to irreversible paralysis, typically in the legs. Before widespread vaccination, polio paralyzed tens of thousands of children every year. The virus still circulates in parts of the world, and anyone who is unvaccinated can contract it regardless of age.
Whooping cough (pertussis) is another disease where vaccination status dramatically changes outcomes. During a 2023 outbreak in Jerusalem that spread primarily through unvaccinated communities, 24% of infected infants were hospitalized. One previously healthy 10-week-old infant, whose mother had not been vaccinated during pregnancy, died. Infants under one year old accounted for 80% of all pertussis hospitalizations during that outbreak.
Measles Can Erase Your Existing Immunity
One of the lesser-known consequences of skipping the measles vaccine is what happens to your immune system after a measles infection. Measles doesn’t just make you sick for a couple of weeks. It destroys a portion of your immune system’s memory cells, the cells responsible for “remembering” infections and vaccinations you’ve already had. Scientists call this immune amnesia.
After recovering from measles, your body loses some of the antibodies it previously built up against other diseases. This means you can become vulnerable again to illnesses you were once protected against. Studies have found that children remain more susceptible to other infections for one to three years after a measles infection. So the true cost of measles isn’t just the disease itself; it’s the cascade of other infections that follow because your immune defenses have been partially reset.
Natural Infection Is Riskier Than Vaccination
Some people reason that catching a disease naturally will build stronger immunity than a vaccine. While natural infection does produce an immune response, the price you pay to get it is the full risk of that disease, including its worst complications. Measles can cause brain swelling. Polio can paralyze. Whooping cough can suffocate infants. These aren’t rare edge cases; they’re well-documented outcomes that vaccines were specifically designed to prevent.
When researchers have weighed the risks of vaccination against the risks of natural infection across multiple diseases, all three key factors (the level of risk, the reliability of the immune response, and how long protection lasts) consistently favor vaccines as the safer path. Adverse effects from vaccines are minimal compared to the dangers of the diseases themselves.
Community Protection Breaks Down
Vaccines don’t just protect individuals. When enough people in a community are vaccinated, diseases can’t easily spread from person to person. This collective shield, known as herd immunity, protects people who genuinely can’t be vaccinated: newborns too young for their first shots, cancer patients on chemotherapy, organ transplant recipients on immune-suppressing drugs.
The threshold for herd immunity depends on how contagious the disease is. Measles is one of the most contagious viruses known. A single infected person can spread it to 12 to 18 others in a susceptible population, which means about 95% of people need to be vaccinated to keep measles from spreading. Polio requires around 80% coverage. When vaccination rates drop below these thresholds, outbreaks become inevitable.
That’s exactly what’s happening now. U.S. national MMR vaccination coverage among kindergartners dropped from 95.2% in the 2019-2020 school year to 92.5% in 2024-2025. That gap of less than three percentage points left roughly 286,000 kindergartners unprotected and pushed coverage below the 95% threshold needed to contain measles. The result: 2,283 confirmed measles cases in the U.S. in 2025 across 50 separate outbreaks, with 90% of those cases linked to outbreaks in communities with lower vaccination rates.
Unvaccinated individuals also transmit diseases more effectively than vaccinated people who happen to get infected. Breakthrough cases in vaccinated people carry a much lower risk of spreading the virus to others.
Practical Consequences for School and Travel
Every U.S. state currently requires children to be vaccinated against certain diseases to attend public school. The universally required vaccines cover measles, mumps, rubella (MMR), diphtheria, tetanus, pertussis (DTaP), polio, and chickenpox. Some states also require hepatitis A, hepatitis B, or meningococcal vaccines.
Almost all states (47, plus Washington, D.C.) allow exemptions for religious or personal beliefs in addition to medical exemptions. Only California, Connecticut, Maine, and New York limit exemptions to medical reasons. The share of children claiming exemptions hit 3.6% in the 2024-2025 school year, the highest national rate ever recorded, up from 2.5% just five years earlier. Research consistently links higher exemption rates to lower vaccination coverage and increased outbreak risk.
Some states are moving to loosen requirements further. Idaho passed a law in 2025 prohibiting vaccine mandates, allowing healthy unvaccinated children to attend school even during an active outbreak. Florida has proposed eliminating all school vaccination requirements entirely, which would make it the first state to do so. On the other end, West Virginia is in the middle of legal disputes over an executive order that would expand exemptions beyond medical reasons.
If your child is unvaccinated and an outbreak occurs at their school in a state that still enforces mandates, they can be excluded from attending until the outbreak is contained. That can mean weeks of missed classes. For international travel, many countries require proof of specific vaccinations for entry, and traveling unvaccinated to areas where diseases like measles or yellow fever circulate puts you at serious risk.
The Risks Fall Hardest on the Vulnerable
The consequences of not vaccinating extend well beyond the individual making the choice. Infants are the most obvious example. Babies can’t receive their first MMR dose until 12 months of age, which means they depend entirely on the immunity of the people around them. In the 2023 pertussis outbreak in Jerusalem, 84 out of 100 mothers of infected infants had not received a pertussis vaccine during pregnancy, leaving their newborns without even the passive protection that maternal antibodies provide.
Elderly adults, people undergoing cancer treatment, and those with autoimmune conditions face similarly elevated risks. These groups often can’t mount a strong immune response to vaccines even when they do receive them, so they rely on high vaccination rates in the surrounding population to avoid exposure. When that community protection erodes, the people who pay the highest price are rarely the ones who made the decision to skip vaccination.