Measles, Mumps and Rubella (MMR): The Diseases & Vaccines

April 2025

In this video, Dr. Paul Offit describes three important lessons from the current measles outbreak in Texas, including higher than reported cases, low vaccination rates, and harm from use of vitamin A.

Watch the video.

Measles, mumps and rubella are all viral infections that caused widespread illness in the past.

Vaccines to prevent each disease were first developed in the 1960s and then combined to form the MMR vaccine in the 1970s.

View a full-size image of the infographic: English | Spanish.

The diseases

Measles

The face of measles

In 1991 the city of Philadelphia was in the grip of a measles epidemic. At the center of the epidemic were two religious groups that refused immunizations for themselves and their children. Children with measles developed high fever; a red, raised rash that started on the face and spread to the rest of the body; and "pink eye." For some, the disease got much worse. Six children in these church groups and three children in the surrounding community died from measles.

By 2000, due to effective use of vaccine, measles was essentially eliminated from the United States. However, in 2019, almost 1,300 cases were reported to the Centers for Disease Control and Prevention (CDC). Of those, 128 people were hospitalized and 61 experienced complications, including pneumonia and encephalitis (inflammation of the brain). This was the largest U.S. outbreak in almost 30 years. The reason: some parents were choosing not to vaccinate their children. Although the number of cases was not as high in subsequent years, each year measles cases have continued to occur in the U.S.

What is measles?

Measles is a disease that is caused by a virus. People with measles may have some or all of the following:

A fever that gradually goes up to 103°-105° Fahrenheit
Cough, runny nose, pink eye
Raised, bluish-white spots inside the mouth
A rash consisting of red spots, raised in the middle. The rash begins at the hairline and moves to the face and neck before descending downward and outward over the rest of the body
Diarrhea
Lack of appetite

Watch as Drs. Paul Offit and Katie Lockwood from CHOP talk about measles, its symptoms, complications, how it’s spread, what doctors worry about, and more.

Doctors Talk: Measles
Katie Lockwood, MD: So, I remember learning in medical school that measles has fever and then those three Cs: cough, runny nose and conjunctivitis, and then the rash comes later, but that looks like a lot of the different viral infections that I see in primary care in kids. I know the rash looks a little bit different, but until that point, I imagine it's pretty hard to tell measles from other viruses.

Paul Offit, MD: Not hard at all. When children come into our hospital, Children's Hospital of Philadelphia, and there's a suspicion of measles, they ask older people like me to come down and take a look because honestly, I can tell within 30 seconds whether somebody has measles.

Katie Lockwood, MD: And 1 in 5 kids with measles were hospitalized.

Paul Offit, MD: You're right. I mean, measles causes congestion, cough, runny nose, and rash and pink eye. And the rash usually starts at sort of the hairline here and then spreads down to the face, the trunk and then out to the arms and legs. And the rash is the so-called measles-like rash, but there are rashes that look similar. So, you could argue, how do you distinguish fever and a rash in someone who has measles from fever and a rash in these other viral infections that can do the same thing? And the way that you do that is children with measles are sick. You can really tell within 30 seconds of walking into the room who has measles and who doesn't because children with measles are miserable.

Katie Lockwood, MD: And then there are long-term complications from measles that we don't see with many routine childhood illnesses.

Paul Offit, MD: That's right. So, measles causes the rash we all know about, but it also can cause severe and occasionally fatal pneumonia. Measles can also infect your brain. And every year in this country before there was a measles vaccine, which was first available in the early 1960s, we would see 48,000 hospitalizations with measles, and we would see 500 deaths from measles. But there's one long-term complication of measles that I think few people know about and has the fancy name subacute sclerosing panencephalitis, and that's just a progressive neurological degeneration. Initially, it starts as sort of poor handwriting and then eventually an invariably progresses to death. And once that symptom cascade starts, it's inevitable that it's a fatal outcome.

Katie Lockwood, MD: But the measles vaccine is a live vaccine. So, I would imagine that some parents would worry that they could have that SSPE complication from the vaccine. We don't see that though.

Paul Offit, MD: No. The key is not just live, it's live attenuated. So, it is a highly, highly weakened form of the virus. So, it induces the immunity that's a consequence of the natural infection without having to pay the price of natural infection, and it worked. I mean measles is the most contagious of the vaccine-preventable disease. I mean if someone comes into our hospital and into one of the rooms in the emergency department, no one can go in that room for another two hours until all those tiny little droplets settle. But, nonetheless, we were able to eliminate measles from this country by the year 2000. Unfortunately, measles has to some extent come back because a critical number of parents have chosen not to vaccinate their children.

Katie Lockwood, MD: The contagiousness is what worries me the most as a primary care doctor. As you mentioned, it hangs out in the air for a while, and if you're not vaccinated and you're in the same space as someone with measles, 9 out of 10 of those people will contract measles, which is unlike any other infection that's in my waiting room, which is so scary because there have been periods in time where many people are not getting measles vaccine, and we see outbreaks even in the U.S. because people travel.

Paul Offit, MD: You're right. It's frightening. Take a disease like smallpox, which was fatal 30-plus percent of the time, but that was spread by large droplets. You really need to have face-to-face contact with someone with smallpox to get that disease. For coronavirus, for this virus, the COVID virus, it's generally small droplets. So again, you need to be, you know, fairly close to somebody who has that virus and then is spreading it via talking or sneezing or coughing. Measles is spread by aerosol. So, it just, it's very, very tiny droplets that can hang in the air like a ghost before they settle down, and that's what makes that virus so remarkably contagious.

Katie Lockwood, MD: In 2019, we saw some of the highest rates of measles in the United States since the early '90s, and we think that some of that is due to people refusing the vaccine. During the pandemic with social distancing, we were distancing, and we didn't see measles, thankfully, but I do worry that as we start coming back together again that we might see measles coming back.

Paul Offit, MD: I think you're right. I think what worries me actually is that because of this pandemic, children have become undervaccinated for a variety of potential infectious diseases, and I really do feel that as we all now get back together again and unmask and no social distance that you're going to see some of these vaccine-preventable diseases come roaring back in that group that is unvaccinated.

Katie Lockwood, MD: And you're right that we forget about how serious measles is because many people who were born after the vaccine haven't seen it, and it does feel like something that was just in the textbook. But as you mentioned, these kids get so sick that it's something that we can't forget about.

Paul Offit, MD: I think you're right. I think at some level vaccines have become a victim of their own success.

When you see some young parents today say, you know, I'll take the measles every time, it tells me that not only have we largely eliminated measles from this country, I think we've eliminated the memory of measles because measles makes you sick.

Transcript Transcript

How does measles spread?

When an infected person coughs or sneezes, measles viruses are spread in the small respiratory droplets. If a susceptible person breathes in these droplets or touches an infected surface and then puts their hand in their mouth or nose, they are likely to get measles.

How contagious is measles?

Measles is one of the most contagious diseases. In fact, if 100 susceptible people are in a room with someone who is infected, 90 of them are likely to become ill with measles. Further, if someone who has not had measles enters an elevator or other small space up to two hours after an infected person has left, they can still “catch” measles.

Are there complications from measles infections?

Yes. About 3 of every 10 people who get measles will develop complications such as:

Ear infection
Pneumonia
Encephalitis (swelling of the brain)
Subacute sclerosing panencephalitis (a disease characterized by progressive neurological deterioration and early death)
Hemorrhagic measles – includes seizures, delirium, difficulty breathing and bleeding under the skin
Clotting disorder
Death

Pregnant women who are infected with measles can miscarry, deliver early, or have a low-birth-weight baby. People who are immune compromised are at risk of having prolonged and severe illness.

Measles infections can also pave the way for other bacterial and viral infections — even several years later. This may happen because measles infections can wipe out preexisting immunologic memory cells that protect against other infections, such as influenza. Because this same damage to immunologic memory doesn’t happen following vaccination, the measles vaccine also protects the integrity of the immune system.

What if I suspect measles?

Call your healthcare provider and mention your concern. Because measles is so contagious, providers typically do not want infected patients sharing a waiting room with other patients. This is particularly important for infants who are too young to receive the vaccine.

Mumps

The face of mumps

Before the mumps vaccine, mumps was the most common cause of meningitis (swelling of the lining of the brain and spinal cord) in children. Virtually all children recovered from meningitis, but some were left with permanent deafness. In fact, before a vaccine was available, mumps was the most common cause of acquired deafness in the United States. The vaccine was developed when vaccine researcher, Maurice Hilleman, isolated mumps virus from his daughter, Jeryl Lynn, when she was 5 years old and became ill with mumps. For this reason, the vaccine strain of virus is referred to as the “Jeryl Lynn strain.”

Watch a clip from HILLEMAN: A Perilous Quest to Save the World’s Children to learn more about Dr. Hilleman’s efforts to create mumps vaccine.

What is mumps?

Mumps is a virus that usually causes swelling in the salivary or parotid glands, just below the ear, lasting for about seven to 10 days. The swelling may occur on one or both sides of the face, causing a chipmunk-like appearance in infected people. This may be accompanied by muscle aches, fatigue, lack of appetite, headache and low-grade fever.

While many mumps infections are mild, not all are. Mumps can infect testicles, causing a disease known as orchitis in up to 1 of every 3 infected males. Some men with orchitis were found to be sterile after the infection resolved. Additionally, mumps infection during pregnancy occasionally resulted in the death of the unborn child.

Rubella

The face of rubella

Before the rubella vaccine, children infected with rubella would develop a light, mild rash on the face. Some children would also develop swelling of the lymph glands behind the ear. Rubella was a mild infection of childhood. But in 1941, an Australian eye doctor made a curious observation. He found that many children were born with congenital cataracts and blindness following an outbreak of rubella. This was evidence that rubella could permanently damage the developing fetus.

What is rubella?

Rubella is a viral infection, also known as German measles. Rubella infection of children causes a mild rash on the face, swelling of glands behind the ear, occasionally a short-lived swelling of small joints (like the joints of the hand), and low-grade fever. Children virtually always recover from rubella infection without consequence.

But rubella is not always a mild infection. Before the rubella vaccine as many as 20,000 babies were born every year with birth defects because of the capacity of rubella virus to infect the unborn child. In fact, 85 of 100 women infected with rubella in the first trimester of pregnancy had babies that were permanently harmed. Rubella virus can cause blindness, deafness, heart defects or mental deficits in infants whose mothers were infected early in pregnancy.

Watch this short film, Stanley Plotkin: Pioneering the Use of Fetal Cells to Make Rubella Vaccine, to see how determined scientists were to protect women from rubella infection during pregnancy.

Rubella parties

While rubella was not typically a severe childhood illness, it could be fatal when pregnant women were infected. Before the vaccine, each year about 20,000 babies were harmed when their mothers were infected during pregnancy. For this reason rubella parties were recommended by pediatricians to ensure that young girls were exposed before they were old enough to become pregnant. Today, with the availability of a vaccine, doctors and parents can be assured that children are becoming immune to these diseases in the safest way possible.

Measles Q&A

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Mumps Q&A

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The vaccines

MMR vaccine

The MMR vaccine contains vaccines that protect against three viral infections: measles, mumps and rubella. MMR vaccine is given as a series of two doses with the first dose at 12 to 15 months of age and the second at 4 to 6 years of age.

Watch as Dr. Offit talks about the safety of the MMR vaccine in the short video below, part of the series Talking About Vaccines with Dr. Paul Offit.

Is the MMR vaccine safe?
Paul Offit, MD: Hi, my name is Paul Offit. I’m talking to you today from the Vaccine Education Center, here at the Children’s Hospital of Philadelphia.

Probably one of the more common questions we get asked here at the center is, “Is the MMR vaccine safe?” MMR stands for measles, mumps, rubella. The shorter answer is, yes. But where this comes from — where the fear comes from — is that there was a paper published in a medical journal called The Lancet in 1998 claiming that that vaccine, the MMR vaccine, increased one’s risk of autism. It was really just a case series; it was a report of 12 children, eight of whom had autism within a month of receiving that vaccine. So, what you could argue is that the best thing that that paper might’ve done was it raised the question, “Could MMR vaccine cause autism?” Because certainly some parents could say, reasonably, “Look, my child was fine, they got this MMR vaccine, and now they’re not fine. Now they have autism. They have signs and symptoms of autism. Could the vaccine have done that?”

The good news is that’s a scientific question; that’s an answerable questions. It can be answered in a scientific venue, and it has been. There have now been 18 studies, done in seven different countries, on three different continents, involving hundreds of thousands of children, and costing tens of millions of dollars, to look at groups of children who either did or didn’t get the MMR vaccine, making sure that those two groups were alike in all other aspects — healthcare-seeking behavior, socioeconomic background, medical background — so you could isolate the effect of that one variable: receipt of MMR vaccine. And study after study after study, now 18 studies have shown that you’re at no greater risk of getting autism if you got the MMR vaccine or if you didn’t.

So, I think you can now say that that question has been asked and answered. And certainly now where we’re seeing more and more cases of measles because people … some parents are choosing not to vaccinate their children, it’s become more important than ever to make sure that you get the MMR vaccine because measles is a bad disease. I mean before there was a measles vaccine in this country in the 1960s, every year about 3 million people would get measles, mostly children less than 15 years of age, 48,000 would be hospitalized, and 500 would die — die when measles virus infected the lungs and caused pneumonia, or die when measles virus infected the brain and caused encephalitis. So, it’s an important vaccine to get, and although I think parents should be skeptical of anything they put into their bodies, including vaccines, I think parents can be reassured that the MMR vaccine is safe.

Thank you.

Transcript Transcript

While the MMR vaccine is the only way to be protected against measles, mumps and rubella, this section describes each vaccine component separately.

Measles vaccine

How is the measles vaccine made?

The measles vaccine is a live, "weakened" form of natural measles virus. To make some vaccines, viruses are "weakened" by a process called "cell culture adaptation" (see How Are Vaccines Made?). "Cell culture adaptation" modifies natural measles virus so that it behaves very differently once it is injected into the body.

Natural measles virus normally grows in cells that line the back of the throat, skin or lungs. Cells are the building blocks of all the different parts of the body, like skin, heart, muscles and lungs. Natural measles virus reproduces itself thousands of times, often causes severe disease, and is passed on to the next person unchanged.

But the process of "cell culture adaptation" changes all of that. Natural measles virus was first taken from someone infected with measles. The virus was then "grown" in cells taken from chick embryos. By growing the virus in chick embryo cells, it became less and less able to grow in human cells. This happened because the genes that tell measles virus how to reproduce itself were changed. Now the virus reproduced itself very poorly.

When this vaccine virus (a now modified form of the natural virus) is put back into the body, it grows very poorly. Whereas natural measles virus reproduces itself thousands of times during natural infection, the measles vaccine virus reproduces itself probably fewer than 20 times. That is why natural measles virus causes illness, but measles vaccine virus doesn't. However, because the measles vaccine virus reproduces itself a little bit, it induces immunity against measles that is life-long. (See how vaccines work.)

The effectiveness of the measles vaccine has been dramatic. Before the first measles vaccine became available in the United States (in 1963), 3-4 million people were diagnosed with measles, about 48,000 were admitted to hospitals and about 500 people died every year.

Decreases in the use of the MMR vaccine have led to increasingly larger measles outbreaks. For example, in 2019, the U.S. experienced the largest outbreak in almost 30 years with almost 1,300 cases reported to the CDC. These outbreaks occurred because a critical number of parents had chosen not to vaccinate their children. While cases of measles decreased during the years of the COVID-19 pandemic, due to fewer opportunities for the virus to spread, a few cases occurred each year and the annual number of cases has again started to increase. Sadly, given that vaccine hesitancy and misinformation remain issues post-pandemic, it is likely that we will continue to see this virus spread.

What are the side effects of the measles vaccine?

The measles vaccine causes some children to develop soreness in the local area of the shot, and occasionally a low-grade fever, after receipt of MMR. Reports have also indicated rare cases of fevers greater than 103 degrees Fahrenheit, usually five to 12 days after receiving the shot. In some children (about 1 of every 3,000-4,000 children), the fever may increase rapidly causing a fever-associated seizure. Known as febrile seizures, these seizures, while scary, do not cause long-term harm. (You can find out more about fever and this type of seizure on the Q&A, Infectious Diseases and Fevers: What You Should Know.”)

Also, some children develop a mild, measles-like rash about seven to 12 days after getting the MMR vaccine. Children with this reaction can still get the MMR vaccine in the future. Children with measles rash from the vaccine are not contagious to other people.

Because the measles vaccine is made in chick embryos, it was once thought that children with egg allergies should not receive the MMR vaccine. This is no longer the case. Studies showed that even children with severe egg allergies could receive the MMR vaccine without consequence.

Rarely, the combination measles-mumps-rubella (MMR) vaccine can also cause a short-lived decrease in the number of platelets that circulate in the body. Platelets are cells that help the blood to clot, such as, for example, after the skin is cut. This reaction occurs in roughly 1 of every 24,000 people who receive the vaccine and has never been fatal.

Mumps vaccine

How is the mumps vaccine made?

The mumps vaccine virus is "weakened" by a process called "cell culture adaptation." (see How Are Vaccines Made?). "Cell culture adaptation" modifies natural mumps virus so that it behaves very differently once it is injected into the body.

Natural mumps virus normally grows in cells of the salivary glands. Cells are the building blocks of all the different parts of the body, like skin, heart, muscles and lungs. Natural mumps virus reproduces itself thousands of times, occasionally causes severe disease, and is passed on to the next person unchanged.

But the process of "cell culture adaptation" changes all of that. Natural mumps virus was first taken from a little girl named Jeryl Lynn Hilleman. Jeryl Lynn was the 5-year-old daughter of Dr. Maurice Hilleman, a scientist who, at the time, was working in the research laboratories of a company named Merck, Sharp & Dohme. Dr. Hilleman then "grew" the virus in eggs. By growing the virus in hen's eggs it became less and less able to grow in human cells. This happened because the genes that tell mumps virus how to reproduce itself were changed. Now the mumps virus reproduced itself very poorly.

Watch a clip from HILLEMAN: A Perilous Quest to Save the World’s Children to learn more about Dr. Hilleman’s efforts to create mumps vaccine.

When this vaccine virus (now a modified form of the natural virus) was put back into other children, it grew very poorly. Whereas natural mumps virus reproduces itself thousands of times during infection, the mumps vaccine virus reproduces itself probably fewer than 20 times. That is why natural mumps virus causes illness, but mumps vaccine virus doesn't. However, because the mumps vaccine virus reproduces itself a little bit, it induces immunity against mumps that is life-long. (See how vaccines work.)

Outbreaks of mumps continue to occur throughout the U.S. These outbreaks are the result of lower vaccine use as well as waning immunity against the most commonly circulating type of mumps virus. Many recent outbreaks have occurred on college campuses. Between 2014 and 2019, more than 1,000 cases of mumps occurred each year with the peak of over 6,000 cases per year during 2016 and 2017. While numbers decreased beginning in 2020, they have started to slowly rise again as we returned to pre-pandemic activities. Hopefully, they will not return to the frequency seen during the years leading up to the COVID-19 pandemic. During outbreaks, a third dose of mumps-containing vaccine may be recommended for those at increased risk of exposure.

What are the side effects of the mumps vaccine?

After receiving the mump vaccine, children may develop soreness in the local area of the shot, and occasionally a low-grade fever.

Because the mumps vaccine is made in chick embryo cells, it was once thought that children with egg allergies should not receive the MMR vaccine. This is no longer the case. Studies showed that even those with severe egg allergies could receive MMR vaccine without serious consequence.

Rubella Vaccine

How is the rubella vaccine made?

Like the measles and mumps vaccines, the rubella vaccine is a live, "weakened" form of natural rubella virus. The rubella vaccine virus is "weakened" by a process called "cell culture adaptation." (see How Are Vaccines Made?). "Cell culture adaptation" modifies natural rubella virus so that it behaves very differently once it is injected into the body.

Natural rubella virus normally grows in cells that line the back of the throat. Cells are the building blocks of all the different parts of the body, like skin, heart, muscles and lungs. Natural rubella virus reproduces itself thousands of times, occasionally causes severe disease, and is passed on to the next person unchanged.

But the process of "cell culture adaptation" changes all of that. Natural rubella virus was first taken from someone infected with rubella. The virus was then "grown" in human embryo fibroblast cells. These cells were first obtained from an elective termination of one pregnancy in England in the early 1960s. These same embryonic cells have continued to grow in the laboratory and are used to make rubella vaccine today. Fibroblast cells are the cells needed to hold skin and other connective tissue together.

By growing rubella virus in human embryo fibroblast cells, it became less and less able to grow in human cells that lined the back of the throat or in cells of an unborn child. This happened because the genes that told rubella virus how to reproduce itself were changed. Now the virus reproduced itself very poorly.

When this vaccine virus (a now modified form of the natural virus) was put back into other children, it grew very poorly. Whereas natural rubella virus reproduced itself thousands of times during natural infection, the rubella vaccine virus reproduced itself probably fewer than 20 times. That is why natural rubella virus causes illness, but rubella vaccine virus doesn't. However, because the rubella vaccine virus reproduces itself a little bit, it induces immunity against rubella that is life-long. (See how vaccines work.)

There is no better example of how weakened the rubella vaccine virus is as compared with natural rubella virus than the following story: MMR vaccine has been mistakenly given to pregnant women during their first trimester more than 1,000 times. No child born to these mothers was affected by the rubella vaccine. On the other hand, of 1,000 women infected with natural rubella infection during the first trimester, 850 will have children with birth defects.

Watch this short film, Stanley Plotkin: Pioneering the Use of Fetal Cells to Make Rubella Vaccine, to see how determined scientists were to protect women from rubella infection during pregnancy.

Girls are immunized with rubella vaccine to protect their future children

Rubella vaccine is a unique example of not only vaccinating to protect the vaccine recipient, but also vaccinating one person to protect another. We vaccinate girls against rubella so that, if they become pregnant as adults, their unborn children will be protected against the devastating effects of rubella infection. We vaccinate boys to help stop the spread of rubella in the community.

What are the side effects of the rubella vaccine?

Some children experience soreness in the local area of the shot and a low-grade fever. Children may also develop a mild rash that is not contagious to other children.

The rubella vaccine can also cause arthritis (swelling and pain in the joints) in some women (usually those older than 14 years), but the arthritis is short-lived and doesn't cause permanent harm. The rubella vaccine is also an extremely rare cause of short-lived arthritis in young children.

Relative risks and benefits