No vaccine in the history of vaccines has more controversy associated with it than MMR (measles, mumps, and rubella). Ask Science looks at the truth behind this controversial vaccine and its connection to autism.
Few things have had a greater impact on human health than the development of vaccinations. Sicknesses that our parents and grandparents used to fear are now almost completely unheard of. Despite these benefits, some people view vaccines with skepticism and even fear; and of all the vaccines, none is more mistrusted that the measles, mumps, and rubella, or MMR, vaccine which some people believe can cause autism. So is there any truth to this belief? Does the MMR vaccine really cause autism?
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The Best Defense
There are different kinds of vaccines, but they all work by taking advantage of the immune system’s natural response. The immune system is relatively complex, but at its most basic it’s simply a defense mechanism. So when any foreign particle enters your body that your immune system doesn't like, it marshals two main armies of cells to deal with it.
The first division of this army goes to work, rapidly destroying the foreign particles and any cells already infected with them. The second division of cells goes dormant and becomes what are called "memory cells." These memory cells can remain in an inactive state for many years until they later encounter another foreign particle of the same type. When they do, the memory cells rapidly reactivate and respond to the intruder, acting before the infection can take hold.
It's sort of like defending your home against burglars. One method would be sit in your living room and wait for a burglar to come, then engage him in hand to hand combat. Another method would be to train a pack of ferocious guard dogs to recognize his scent, and then station thousands of them all around your house. While the first method might work, the second method would most likely be faster and allow you to get more sleep at night.
Vaccination against a particular disease involves introducing something to the immune system that will allow the body to create these memory cells without giving them the actual illness. The vaccine can consist of a weakened (or live attenuated) virus or bacteria, or dead (inactivated) virus or bacteria, their component parts (component vaccines), or inactivated toxins that the virus or bacteria create during infection (toxoid vaccines).
The MMR vaccine consists of the measles, mumps, and rubella vaccines administered in a single dose. The vaccine has resulted in nearly the complete eradication of these illnesses from the United States and from many other parts of the world that have similar vaccination programs.
In the 1960s there were around 500,000 reported measles cases in the United States every year. The measles vaccine was introduced in 1963, and by 1970 the number of measles cases in the U.S. had dropped to under 50 cases per year. However, in the past three years the number of measles cases is on the rise again, with more cases this year than the past 15 years combined. This is particularly alarming when you consider that roughly one out of every three people who contract measles needs to be hospitalized, and one out of every thousand children who contract measles will die.
So what's behind this sudden spike in measles cases? Has measles mutated into some kind of super bug, outsmarting our vaccinations? No, the problem is that a growing number of people have decided to not give their children the MMR vaccine, based solely on the rumors and fear generated by media coverage of one man's research from 1998.
Dr. Andrew Wakefield
In 1998, Dr. Andrew Wakefield and his colleagues were studying a possible link between the MMR vaccine, autism, and gastrointestinal disease. Their paper concluded with this statement:
"We did not prove an association between measles, mumps, and rubella vaccine and the syndrome described. Virological studies are underway that may help to resolve this issue."
And although at a press conference following the release of the paper, Dr. Wakefield himself said only that he thought the combined dose should be replaced with individual doses until more studies could be done, the MMR vaccine has become forever fixed in the minds of many parents as one of the direct causes of autism.
Since the Wakefield paper, several studies have been carried out which failed to show any link between the MMR vaccination and autism. One particularly important study looked at the effect that a complete withdrawal from MMR vaccine had on a population’s incidence of autism. Starting in 1993 Japan terminated its MMR vaccination program, using only individual shots instead of the combined MMR. The study found that there was no decline in the occurrence of autism following this change.
There's plenty of controversy surrounding the original Wakefield paper, (which was eventually retracted by the journal it was printed in). However, Ben Acre, author of Bad Science, points out that a large share of the blame for the widespread belief in the link between autism and MMR lies with the media, who as we know likes to sensationalize science. Dr. Acre points out that while several studies have since been carried out refuting Wakefield's claims, none of them have received the extensive media coverage that the original paper did.
The take home message from all of this is that while vaccines, like all medical treatments, certainly carry some side effects, autism is not likely one of them. The risks associated with side effects of the MMR vaccine are extremely small compared to the risks associated with contracting measles.
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