Side Effects of the MMR Vaccine


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Most medical treatments carry with them the risk of causing some side effects, and vaccines are no exception. In this article we take a brief look at what the side effects of the MMR vaccine are and how they are caused.

Why does the MMR vaccine have side effects?

Side effects as a result of vaccination are caused by how vaccines work more than anything else. A vaccine is essentially a specially designed formula composed of parts of a virus or bacterium, or in some cases a weakened version of that virus or bacterium. The MMR vaccine falls into the latter category, and is made up of the weakened versions of the bacteria responsible for the measles, mumps, and rubella infections.

Once the vaccine has been introduced into your body, it confers immunity by triggering your body’s response against external disease causing organisms. We all possess an immune system which is the defensive mechanism working on behalf of the human body. This immune system responds to invading organisms and, after an initial exposure, is more readily able to deal with subsequent infections.

Some infections can overwhelm the immune system, and in doing so cause diseases like measles which can, in some cases, be fatal. Vaccination prepares the body for future infections, meaning that if the measles virus does cause an infection, it won’t be as severe.

Side effects can sometimes occur because of the body’s reaction to the weakened virus in the vaccine. The immune system is acting against an invader in this case, and so some of its mechanisms, like fever, present as side effects. A fever is a great example, as in most cases it’s actually an effective way of getting rid of an infection. By increasing your body temperature, the immune system makes it difficult for a disease causing pathogen or bacterium to survive.

What are the side effects of the MMR vaccine?

The main side effects of the MMR vaccine are a mild fever which 1 in 10 children will develop. This is often accompanied by a rash and malaise, and can last for up to 16 days. These side effects typically begin about 5 days after the injection, and usually only occur after the first dose provided by the childhood vaccination scheme (there are two doses provided by the NHS). About 1 in 20 children develop temporary pain in their joints.

In very rare cases vaccines like the MMR can cause an extreme allergic reaction called anaphylaxis. This usually involves collapse and difficulty in breathing, but fortunately medical staff are prepared and trained to quickly administer treatment. Anaphylaxis is extremely rare, and is thought to be caused by egg allergies. Some of the viruses in the MMR injection are grown in chicken eggs, hence the connection between the two.

Previous versions of the vaccine made use of a particular type of mumps virus called the Urabe strain. This was linked to rare neurological problems like viral meningitis, and so the Urabe strain is no longer used for the MMR vaccine in the UK. The mumps virus used in MMR is now derived from the Jeryl Lynn strain which, while more expensive, is much safer.

A paper published in 1998 that suggested a link between the MMR vaccine, autism, and Crohn’s Disease has since been discredited. A number of independent authorities have proven that the vaccine does not cause either of the diseases mentioned, and the author of the study has since been discredited for falsifying evidence and other ethical issues.

While the MMR vaccine used today does carry with it a small risk of side effects, it is widely acknowledged that the benefits offered by the vaccine far outweigh the potential risks. Measles, mumps, and rubella are all extremely contagious conditions that can cause serious complications, which is why the widespread use of the MMR vaccine has been such a great asset to healthcare around the globe.


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