Yes, the MMR vaccine is safe

The MMR vaccine, which protects against measles, mumps, and rubella, has been available since 1971. In the more than 50 years since then, tens of millions of babies and children have been followed and studied to track both the immediate and long-term impacts of the vaccine.

Here is what we know about the safety, potential side effects and risks of the MMR vaccine today.

The MMR vaccine does not cause autism

Autism is a developmental disorder that affects around one in every 100 children. It is caused mainly by genetics – in fact, evidence indicates that autism is about 80 per cent heritable. 

There is no evidence that it is caused by any vaccination, including the MMR vaccine.

The origins of this myth date back to the 1990s, when a paper published in the scientific journal Lancet speculated that there might be a link between the MMR vaccine and autism. This paper, which looked at just 12 children, did not show that the MMR vaccine caused autism. It also was riddled with problems, errors and falsehoods. When they were uncovered, the journal formally retracted the paper. 

The lead author was later exposed as having financially benefited from lawsuits filed against vaccine-producing companies, as well as for having registered his own, competitor vaccine. He has been banned from practicing medicine.

Since then, scientists have tracked the development of hundreds of thousands of children around the world. No study has found any evidence of a link between the MMR vaccine and autism. 

One 2002 study of more than 535,000 children in Denmark, for example, found no difference in the rates of autism between children who were and were not vaccinated. Other studies have replicated these findings in the UK, US and elsewhere. 

While some parents have stories of their children developing signs of autism after being vaccinated, scientists agree that this is because of coincidental timing. The first signs of autism tend to show up around 12 to 18 months of age. The first dose of the MMR vaccine is given between 12 and 15 months of age. It can be extremely disorienting for a child to appears to be developing normally to begin to show symptoms of autism, and it is normal for parents to believe it must be because of a single event, like a vaccine. But this does not make it true.

The side effects of the MMR vaccine

When side effects from the MMR vaccination occur, they are usually mild and temporary, like swelling and soreness at the injection site. In the combined MMR-varicella (MMRV) vaccine, a rash occurs in about 6 in 100 children. Fever occurs in 27 out of 100. In the MMR vaccine that does not vaccinate for varicella (chickenpox), about 2 in 100 children develop a rash, and 19 in 100 experience a fever. If they occur, both of these potential side effects tend to show up around seven to 11 days after vaccination and resolve on their own.

Serious adverse reactions to the MMR vaccine are very rare, such as immune thrombocytopenic purpura. This is bruising that happens when, as a result of an immune system reaction, the blood produces fewer platelets than usual. This occurs in about one per 20,000 doses and is temporary in the vast majority of children. Serious allergic reaction (anaphylaxis) occurs in less than one per 1 million doses

The risk of such reactions to the MMR vaccine also need to be compared to the risk of having similar reactions in response to an infection that the MMR vaccine protects against. 

For example, for every 10,000 children who receive the combined MMRV vaccine, around 8.5 may experience a febrile seizure. These are convulsions that occur in response to a fever. While they can be scary, they do not normally cause any long-term health problems. 

Meanwhile, for every 10,000 children who get measles, around 23 will experience a febrile seizure. In other words, the chance of having a febrile seizure from contracting measles is about 2.5 times greater than the risk of having one after the MMRV vaccine.

Meanwhile, no deaths in healthy children ever have been shown to be related to receiving an MMR vaccine. However, if an unvaccinated child contracts measles, they have a 1 in 500 chance of dying if they are in a middle- or upper-income country. In some populations in lower income countries, the risk of an unvaccinated child dying from measles is much higher. 

The MMR vaccine for children with allergies

Like all vaccines, the MMR vaccine has trace amounts of other ingredients in it, including of antibiotics and gelatin. As a result, if a child has a history of severe allergic reaction in response to antibiotics or gelatin, the MMR vaccine is usually not recommended. It's important to discuss with your child's health provider. 

There is no indication that the MMR vaccination poses a risk to children who have egg allergy.

The risks of measles, mumps and rubella

Measles outbreaks are on the rise. In populations with lower rates of vaccination, mumps and rubella also remain a risk. When weighing the pros and cons of vaccination, it is important to know what these diseases can cause in people who are unvaccinated. 

Measles is an extremely contagious and potentially lethal disease. For every one person who has measles, 12 to 18 other people will be infected if they have not been vaccinated, making measles more contagious than influenza, Ebola, Covid-19 or chickenpox. While it may be mild for some people, it can be very dangerous, and even lethal, in others. In the US, it is estimated that for every 1,000 children who contract measles, one or two will die. In lower income countries, the risk is far higher: for every 1,000 children who contract measles, 30 to 60 will die. 

Measles also can "delete" the immune system's memory of other infections, meaning those who contract it are left far more vulnerable to other diseases, like influenza, for weeks or months afterwards. 

You can read more about whether measles is really dangerous here.

Mumps is a virus that can often be mild, even asymptomatic. But it can have serious side effects. One in 1,000 people who contract mumps, for example, will experience encephalitis, which can cause brain damage and death, while around one out of every 20,000 will go permanently deaf. 

Rubella is a contagious viral infection that used to be called "German measles", although it is a different virus. Common symptoms are a rash, fever, nausea and conjunctivitis. However, rubella can be very dangerous to pregnant women and their foetuses, putting them at increased risk of miscarriage, stillbirth and birth defects.