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The anti-vaccination movement often describes measles as a benign condition of childhood, not really a major health problem. The anti-vaxxer movement is wrong. The truth is, measles can be a deadly disease. About two or three out of every 1000 children who contracts measles develops a brain infection resulting in encephalitis. Measles can also leave children blind. Even worse, getting measles destroys a child's immunity to many other diseases, some of which are far more deadly.
Measles Causes Immune Amnesia
Before the measles vaccination became commonly available in the 1960's, millions of children got the infection and tens of thousands of children died from the infection every year. After the measles vaccine became available in 1963, cases of measles in countries where the vaccine was used dropped by over 99 percent.
However, it turned out that vaccinated children weren't just immune to measles. In every country where the vaccine was introduced, childhood infections became less common generally. It was as if the vaccine protected against more than just measles, and in a roundabout way, it does.
The reason the measles vaccine protects against more diseases than just measles is the unusual effects the measles virus has on the immune system. The measles virus kills white blood cells. White blood cell counts fall precipitously about the same time the infection causes the well-known red spots. About a week, later white blood cell counts usually come back to normal. The problem is that these new white blood cells don't "remember" the infections that the old white blood cells had learned how to fight. Even when children recover from measles, their immune systems have to learn how to fight other common infections all over again.
Getting Measles Increases the Risk of Encephalitis and Pneumonia
Immunologist Michael Mina of Emory University in Atlanta, Georgia, in the United States, went through decades of public health records before and after the introduction of measles vaccine. He found that the children who developed measles lost, on average, about 27 months of "memory" in their immune systems. During that 27 months, children who had had measles were more susceptible to pneumonia and also to encephalitis. Sometimes the child's immune system took such a heavy hit that pneumonia and/or encephalitis developed while they were still sick with measles (although this wouldn't happen unless the child was also exposed to the microbes that cause those diseases at the same time as measles), but sometimes pneumonia and encephalitis came along a little later.
Catching measles resets the child's immune system back to the level of activity it had when the child was newborn. The immune system has to learn how fight common childhood infections like colds and flu all over again. Measles also wipes out immunity to diphtheria, typhoid, and whooping cough acquired through other vaccines. This leaves the child vulnerable to these infections not just as a child but also as an adult, when they can be far more severe. It's possible that catching measles wipes out immunity from all the vaccinations the child has received.