March 25, 20256 min readFive Reasons Measles Outbreaks Are Worse Than You ThinkAnd Why Vaccination MattersMeasles is not a disease to take lightlybut it is also very preventable with vaccinesBy Meghan Bartels edited by Lauren J. YoungSigns point the way to a measles testing site on February 27, 2025, in Seminole, Tex. Jan Sonnenmair/Getty ImagesMany people in the U.S. today have no direct experience with measles, a disease that used to infect three or four million people in the nation every year before vaccines became available in 1963. Adults may remember they were vaccinated against the disease in childhood or have only a vague memory the disease is associated with a spotty red rash.But the virus isnt entirely gone: The U.S. has already seen nearly 400 confirmed cases of measles in 2025 to datemore than the total in any year since 2019. We dont see these outbreaks often, but when we do, they do make headlines, says Gabriel Benavidez, an epidemiologist at Baylor University in Texas.With cases on the rise in an outbreak that started in Texas, here are some key things to know about measles.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Measles Makes You More Vulnerable to Other InfectionsMeasles is a nasty virus. It takes a week or two for symptoms to develop, giving the highly contagious virus plenty of time to spread to other people. Once an infection sets in, measles typically causes a high fever accompanied by a cough, runny nose, and red, watery eyes. The characteristic rash begins several days later, and the disease can trigger ear infections and diarrhea as well. And like other respiratory viruses, the initial infection can leave people vulnerable to pneumonia.But thats not all. A common consequence of a measles infection on the immune system is called immune amnesia. The virus appears to attack B cells, which the immune system uses to remember pathogens it has seen before and respond quickly. One key study published in 2019 found that measles can destroy both B cells trained on nonmeasles infections and so-called naive B cells that respond to future infections. Limited evidence suggests that this reduced immunity can last for a couple years.Measles Can Cause Brain InflammationA rarer complication of measles that occurs in only about one in every 1,000 cases is brain inflammation, or encephalitis. This appears to occur when the measles virus triggers the immune system to attack a protein produced by certain brain cells. The resulting inflammation kills about one in five people.Even when someone appears to recover fully from measles, a serious risk remains in the form of a very rare but near-universally fatal condition called subacute sclerosing panencephalitis, or SSPE. In SSPE, the person appears to recover fully and is no longer infectious, but the measles virus seems to mutate to avoid detection by the immune system. The virus hides in the brain, lying dormant for up to 10 or 15 years. Here it picks up more and more genetic changes and eventually begins to destroy neurons.Over time, this mutated virus can begin to reproduce and cause brain damage, says Walter Orenstein, an epidemiologist and professor emeritus at Emory University. Its just a virus that goes unchecked and destroys brain tissue, and we have no therapy for it.Vitamin A Is Not a CureOne of the most challenging aspects of measles is that doctors can only treat its symptomsthere is no treatment for the infection itself. We do not have a medicine that will make you better, says Sharon Nachman, a pediatric infectious disease specialist at Stony Brook Childrens Hospital.Secretary of Health and Human Services Robert F. Kennedy, Jr., has claimed that vitamin A or cod liver oil rich in the nutrient can treat measles; this is false. There is a nugget of truth here, though: vitamin A is included in U.S. recommendations for measles care, Nachman notes, but it is specifically used to mitigate the infections damage to the eyes, which sometimes causes blindness. Vitamin A supports healthy vision. Its not given for systemic treatment of the virus because thats not what it does, Nachman says.Moreover, vitamin As benefits havent been proved in higher-income countries such as the U.S. Its probably not the same bang for your buck that were getting in countries where children are malnourished, she says. If a human body already has sufficient vitamin A, it will stop metabolizing the substance in order to avoid dangerously high levels of it.Cod liver oil in particular might bring more harm than good, Nachman says: cod liver oil supplements arent regulated by the Food and Drug Administration, so its unclear how much vitamin A they contain, and the products could hide heavy metals or other pollutants that fish are exposed to. Its a natural remedy, [but] that doesnt make it safe, she says.Its All about VaccinesThe best strategy for avoiding the effects of measles, then, as for so many infectious diseases, is simply not to catch the virus in the first place. Fortunately, the two current standard vaccines against measleswhich also include protection against mumps and rubellaare proven to be both very safe and effective. One dose provides 93 percent effective protection against measles and the recommended two doses increases that to 97 percent. (Another vaccine, only available for children between one and 12 years old, also protects against varicella, or chickenpox, but is otherwise similar.)Both formulations of the so-called MMR vaccine contain weakened live forms of the measles virus. The vaccine does occasionally cause mild side effects, such as swelling at the injection site, fever or a mild rash; there is no valid evidence that the MMR vaccine causes autism.When were seeing measles, we need to think that we may also see resurgence of other vaccine-preventable diseases. Walter Orenstein, epidemiologistBut measles vaccination rates in the U.S. are not as high as experts would like. At least 95 percent of people must be vaccinated in order to stop outbreaks from spreading and reduce the possibility that people who are not medically able to be vaccinatedsuch as babies under one year old or immunocompromised peoplewill catch the virus. But the overall measles vaccination rate among kindergarteners nationwide in the 20232024 school year was less than 93 percent. Several states have vaccination rates under 90 percent, and some small regional rates are much lowercreating hot spots vulnerable to outbreaks like the one in Texas.The key weakness of having a strong vaccine but no treatment is that vaccines dont save lives; vaccinations save lives, Orenstein says. A vaccine dose that remains in the vial is zero percent effective, no matter what the clinical trial showed.Vaccination rates fell during the COVID pandemic, when standard preventative care was put on hold. And vaccine hesitancy, which has long swirled around the MMR vaccine, has risen and spread in recent years. But vaccines can also fall victim to their own success by erasing the threat of an infectious disease from peoples minds entirely. Theres a perception of, Well, measles is super rare; its not probably going to happen to me and my community, Benavidez says.Adults in regions with measles cases or who are planning international travel can check their medical records to confirm they received two doses of the vaccine; doctors can also run a blood test to look for antibodies to the virus, which can indicate protectionalthough the test is not always conclusive. Some people may need an additional vaccine dose.Despite Outbreaks, Measles in the U.S. Is Eliminated and Can Remain SoThe vaccine has indeed made measles a rarity. In the U.S. the disease is considered eliminateda formal designation that the nation will lose if the disease spreads internally for a full year.Epidemiologists hope it hasnt come to that. I dont think were going to see widespread measles outbreaks in the U.S., Benavidez says. I think we still do a really good job of vaccinating.But experts say that upticks in measles cases are a clear warning sign that vaccination rates need improvingmeasles is the most contagious of the vaccine-preventable diseases and therefore the one that gains traction first. When were seeing measles, we need to think that we may also see resurgence of other vaccine-preventable diseases, Orenstein says.Measles outbreaks within the country are also a sign the U.S. should bolster vaccination abroad. For more than two decades, all outbreaks in the U.S. have begun when travelers brought the virus in from other nations. The current outbreaks in Texas and New Mexico began with just such an introduction, and the virus merely took hold in vulnerable, undervaccinated regions, whereas in other introductions, cases fizzled out. Supporting vaccination campaigns globallythe disease killed more than 100,000 people worldwide in 2023reduces the likelihood of the virus starting new outbreaks at home as well.Not supporting international immunization efforts not only harms the countries that are no longer receiving the help, but it [also] harms us, Orenstein says.