Before there was a vaccine for it, just about every person in America got measles. They would catch this highly communicable childhood disease usually between the age of 5 and 9. From 1900 to 1960, with improved sanitation, clean water, and better nutrition fostered by rapid delivery of fresh fruits and vegetables along with affordable refrigerators, the mortality rate from measles in the U.S. dropped more than 95 percent.
When I was a child 70 years ago families would have "measles parties" to expose their kids to another child with measles so they could have the disease and get it over with, since everybody eventually got measles anyway.
With its 3-week course of high fevers, sore throat, conjunctivitis, and a rash spreading from the face down one's arms and legs, the vast majority of children come through the illness unscathed and without complications. But one particular complication of measles, encephalitis, spurred doctors to develop a vaccine that would provide protection against this disease, like had been done for diphtheria, pertussis (whooping cough), tetanus, and polio.
After some false starts (in 1963, 1965, and 1967) the live-virus measles vaccine introduced in 1968 proved highly effective in eliminating measles outbreaks. In the 1980s drug companies combined the measles vaccine with the live-virus vaccines for mumps and rubella (some people object that drug companies grow that one in aborted human fetal cells); and it is not possible anymore to obtain a single measles vaccine in the U.S. (single ones are available in the UK and France). Before there was a vaccine for it, there were about a million cases of measles a year in the U.S. Now with its population vaccinated, measles cases averaged less than 100 a year from 2001-2013.
Last year (in 2014) there were 644 cases of measles in the U.S., considerably more than usual (although 383 of them were reported in Amish families who do not vaccinate their children). In January, 2015, there were 102 measles cases across the country, 67 of them in an outbreak in Disneyland, which garnered heightened media attention. (Germany had 254 cases in January with little fanfare.) Emphasizing the importance of vaccination, one magazine writer puts it this way: "Turning Walt Disney's Happiest Place on Earth into the measles kingdom flipped a switch in our collective brain. The thought that thousands of people could have been exposed to a virus that was declared eliminated in the U.S. a decade-and-a-half-ago is scary. And it drives home the reality that vaccines only fully protect us if almost everyone uses them."
MMR vaccination for measles provides immunity against the virus that causes this disease, and people are spared having to suffer through its debilitating manifestations and be subject to possible complications. The MMR shot, however, does not confer lifelong immunity against measles. It only lasts for several years. Booster shots are required, which studies show to be less effective than the initial one.
Health officials, both in the U.S. and UK, blame unvaccinated people and the "anti-vaxxers" for these outbreaks. Assisted by a compliant media, they downplay the fact that the vast majority of people who are contracting measles have been fully vaccinated against it--more than 95 percent in some outbreaks. In the UK, in Northern England, a highly vaccinated part of the country, there were 757 cases in a measles outbreak there in 2013 (January to August). It went unreported. Health authorities steered the UK media in another direction and focused instead on a smaller outbreak in South Wales, which had 40 cases, where vaccine dissenters are more vocal and fewer people have been vaccinated. Unvaccinated people make easy scapegoats in today's climate of vaccine obedience.
The key question, of course, which officials and pundits do not ask (preferring instead to censure "anti-vaxxers"), is: Why would an unvaccinated person pose a danger to the vaccinated population if the vaccine they had is effective and really works?
With measles re-emerging in developed countries where almost all of their citizens have been vaccinated, a call has gone out to develop a better, next-generation measles vaccine. 
One benefit of having measles is that a person so infected will then have lifelong, permanent immunity to it. Mothers transfer antibodies against measles to their babies, which protect them from this disease during their early critical months of life. The MMR shot, however, does not provide lifelong immunity to measles. It only lasts several years, and successively less effective booster shots are required.
There is a second, major benefit of measles that health authorities overlook. Measles helps a child's immune system grow strong and mature.
Once past the immunologic barriers of skin and mucosa, our (2-trillion-cell) immune system has two components: An innate system, which all animals have; and an evolutionarily more recent adaptive system that vertebrates have. The childhood diseases--measles, mumps, rubella, and chickenpox--play a constructive role in the maturation of the adaptive immune system. Two kinds of helper T-cells (Th) manage this system:cellular T-cells (Th1); and humoral T-cells (Th2), which make antibodies. The Th1 cellular T-cells are especially important because they attack and kill cells in the body that run amok and become cancerous. And they also kill cells that become infected with viruses.
Measles (and other viral childhood diseases) stimulate both the Th1 and Th2 components. The MMR vaccine stimulates predominately the Th2 side. Overstimulation of this part of the adaptive immune system provokes allergies, asthma, and auto-immune diseases. Since the Th1 side thwarts cancer, if it does not get fully developed in childhood a person can wind up being more prone to cancer later in life. Women who had mumps during childhood, for example, have been found to be less likely to develop ovarian cancer compared with women who did not have mumps. (This study was published in the mainstream medical journal Cancer.)
Could the fact that cancer has now become a leading cause of death in children be connected to vaccinations? Only a well-controlled, randomized, blinded, long-term scientific trial would be able to conclusively answer this question. But societal entities that could fund such a study, like the government's National Institutes of Health (NIH), drug companies that make the vaccine, or the CDC do not feel that it is necessary to conduct one.