Measles can cause serious complications. The most common are pneumonia, ear infections and diarrhea, and less often brain swelling (encephalitis) or SSPE, a rare and fatal brain disease that can appear years later. The NHS Upwell Health Centre page says complications occur in 10 to 20% of people with measles, and WebMD quotes a pediatric infectious disease specialist putting the death rate at about 1 to 3 in 1,000.
Many readers are asking how dangerous measles really is. Here is what the sources say, section by section.
What are the complications of measles?
The NHS Upwell Health Centre measles page lists the complications below and how often each happens. It says the respiratory (breathing) and gut complications are the most common.
| Complication | What it is | How often, as stated |
|---|---|---|
| Pneumonia | Lung infection | 1 in 20 people. The Upwell page calls it the most common cause of death from measles in young children. |
| Ear infection | Infection of the middle ear | 1 in 10 (Upwell page) |
| Diarrhea | Bowel infection | 1 in 10 (Upwell page) |
| Croup and other airway infections | Swelling of the windpipe and airways | Listed among other complications (DynaMed editors at EBSCO) |
| Encephalitis | Brain swelling. It can cause permanent damage, including deafness and learning disabilities (Upwell page). | About 1 in 1,000 (Upwell page). DynaMed puts primary measles encephalitis at about 1 to 3 per 1,000, with 10 to 15% of these cases fatal. |
| Post-measles encephalitis (ADEM) | Brain inflammation caused by the immune response | About 1 per 1,000. Deaths are 5% in children and 25% in adults (DynaMed). |
| Measles inclusion body encephalitis | Long-term brain inflammation that can arise up to a year after measles | Deaths about 75% (DynaMed) |
| SSPE (subacute sclerosing panencephalitis) | A degenerative brain disease that usually develops 7 to 10 years after infection (Upwell page) | About 1 in 25,000 people with measles (Upwell page and DynaMed). DynaMed gives 1 in 5,500 in infants under one year. The Upwell page says it is fatal. |
| Blindness | Eye inflammation that can lead to blindness (DynaMed) | More likely in malnourished children, especially those with vitamin A deficiency, or those with weakened immunity (DynaMed) |
| Hearing loss | Usually from bacterial meningitis | WebMD says bacterial meningitis is the form most likely to cause hearing loss. |
| Heart problems | Heart muscle inflammation | Possible if the inflammation is severe enough to damage the heart muscle (WebMD) |
Are measles complications rare?
Complications are not rare, but the most serious ones are. The Upwell page says 1 in 5 unvaccinated people in the U.S. who get measles are hospitalized. WebMD says about 1 in 5 people with measles end up hospitalized, mostly children under 5. In 2024, it adds, more than half of children under 5 with measles were hospitalized.
Death is less common. Jeffrey Kahn, MD, PhD, chief of the Division of Pediatric Infectious Disease at the University of Texas Southwestern Medical Center, tells WebMD that the death rate is about 1 to 3 in 1,000. He also says encephalitis happens in about 0.1% to 1% of measles cases, which WebMD compares to the odds of having identical twins.
How deadly is measles worldwide, and in the U.S.?
Researchers measure this with the case fatality ratio, which is the share of people with measles who die. In a measles case fatality paper by Cairns, Nandy and Grais, the authors say the ratio has historically ranged from 0.1% in the developed world to as high as 30% among refugee populations. WHO estimates used in countries where measles is common range from 0.05% to 6%.
The paper also reports measured ratios from studies in five countries. These apply only to the outbreaks and areas named, not to the U.S.
| Setting and year | Case fatality ratio |
|---|---|
| Mirrah district, Niger (2003) | 9.7% |
| White Nile and Khartoum states, Sudan (2004) | 0.9% |
| Nepal, nationwide (2004 to 2005) | 1.1% |
| Moursal, N’Djamena, Chad (2005), children under 5 | 4.0% |
| Dong District, Nigeria (2005), children under 5 | 10.8% |
Counting deaths accurately is hard. The paper says that in places where death records are incomplete, researchers must collect their own data to estimate the death rate.
In the years before the vaccine, WebMD reports, the CDC estimated that measles infected as many as 3 million to 4 million people in the U.S. each year. About 500 people died each year, tens of thousands were hospitalized, and about 1,000 developed encephalitis.
For 2025, the DynaMed editors at EBSCO report that as of March 18, 2025, the Texas outbreak had 279 cases, 36 hospitalizations and one death. For the current 2026 count, check the CDC’s measles updates or your state health department directly.
Who is most at risk from measles complications?
The paper lists the factors thought to affect the death rate: age, how much virus a person is exposed to (household crowding is used as a stand-in), vaccination status, nutritional status, immune deficiency and access to appropriate care. The groups the sources name most often are:
- Young children. Most measles hospitalizations are in children under 5 (WebMD).
- Unvaccinated people. Children who received at least one dose have a lower death rate and fewer complications, according to the paper. WebMD says that in unvaccinated infants younger than 15 months, SSPE risk can be as many as 1 in 600, citing a study by the American Academy of Pediatrics.
- Malnourished children. DynaMed says the eye complications are more likely in children with vitamin A deficiency.
- People with weakened immune systems. Measles can affect immune memory, and the paper lists immune deficiency as a risk factor.
The paper says the major clinical complications that lead to death are pneumonia and diarrhea.
Can measles cause lifelong problems?
Yes. WebMD’s article on the lifelong effects of measles, reviewed April 25, 2025, says long-term side effects “aren’t widely reported or discussed, but they’re real and range from mild to debilitating.” It describes a man who lost his hearing and eyesight after measles in childhood.
Time reports that measles can wipe out immune memory. In a Time report from May 11, 2026, virologist Rik de Swart says that after measles, people can have weaker immunity to common infections, and that in some cases it can take years to get back to normal. Time also reports that a 2015 study led by Michael Mina and de Swart found that measles raised children’s risk of death for two to three years after they had apparently recovered.
Time’s account of the 2015 work used blood samples from unvaccinated children, and it found a loss of immune memory cells.
When do measles complications occur?
Some complications appear during the illness, such as pneumonia, diarrhea and ear infections (Upwell page). Others come later. Measles inclusion body encephalitis can arise up to a year after measles (DynaMed). SSPE usually develops 7 to 10 years after infection (Upwell page). WebMD says SSPE typically appears several years later, when a natural measles infection reactivates in the brain.
How does measles cause complications?
DynaMed explains that measles enters the lining of the eyes, nose and mouth and infects immune cells. The immune response that clears the virus also causes the rash and other symptoms, which begin 10 to 14 days later.
The virus also weakens the body’s defenses. DynaMed says measles increases susceptibility to other infections, including serious bacterial co-infections, and that this effect can last. Pneumonia can come from the measles virus itself or from a secondary bacterial infection.
Time reports that the measles receptor, CD150, is found especially on memory immune cells. According to de Swart, the virus mainly infects and then kills these memory cells.
How do you prevent measles complications?
DynaMed says vaccination is the best way to prevent acute measles infection and avoid these serious complications. The Upwell page says two doses of MMR vaccine give long-lasting protection against measles, mumps and rubella in over 99% of people. It also says that when enough people are vaccinated, the virus has few people to infect, which protects people who cannot be vaccinated.
WebMD says that out of hundreds of millions of vaccinations worldwide, there have been no known deaths in healthy people caused by the MMR vaccine. It reports serious allergic reactions at about 1 in 1 million doses. The vaccine can make you sick if you are severely immunocompromised.
The paper also notes that late-1980s studies linked vitamin A given to measles patients to a drop in deaths of as much as 64%. Ask your clinician whether this applies to you.
What is not known yet?
- The exact death rate is hard to measure in many countries, because deaths often go unrecorded (the PMC paper).
- Long-term effects are not widely reported or discussed (WebMD), so ask a clinician about any lasting symptoms.
- For 2026 death counts, check the CDC’s measles updates or your state health department.
Before you act
- Check your vaccination record, or your child’s, with your clinician.
- If you or your child has measles symptoms, contact a clinician promptly, since pneumonia and diarrhea are the main complications that lead to death.
- Ask your clinician whether an MMR dose is right for you.
- Bring this list to your next primary care visit. You can find more guides on the Primary Care Evidence Guide home page.
By the Primary Care Evidence Guide Team
This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.