As the US faces its worst outbreak of measles since the disease was eliminated in 2000, with almost 900 cases reported, many have put the blame on the anti-vaccination misinformation that has rapidly spread across social media platforms in recent years. And this is certainly a key driver of anti-vaccine sentiment. Social media creates an echo chamber and allows people to hand-pick sources that cater to opinions they’ve already formed. This has fostered widespread skepticism toward authoritative news and science in general.

But we may be overlooking the degree to which the success of those anti-vaccination campaigns is the direct result of the success of vaccines in eliminating diseases. With most Americans no longer having first-hand experiences of measles, vaccines have become a victim of their own success. This complacency could only arise when the dangers of these diseases are forgotten.

The measles vaccine was introduced in 1963, well-within the lifetimes of many adults, but long before most can recall being a parent. Before that, it was the top killer of children in the world, taking 2.6 million lives annually. In 2017, only 110,000 people died from measles.

According to the World Health Organization (WHO), adverse reactions to vaccines occur in one of every million doses of the measles vaccine. But unlike the story of each vaccinated person who avoids a deadly disease to live a long and healthy life, each story of an adverse reaction circulates online fueling fear in populations that are already looking for a reason to avoid vaccines. Meanwhile, the 21.1 million deaths prevented by the measles vaccine between 2000 and 2017 rarely make social media headlines.

Deaths from measles in the US are rare. According to the Centers for Disease Control, the most recent US measles death occurred in 2015. Even before it was eliminated, only about two in every 1,000 US measles cases resulted in death. As a result, many parents may be easily led to believe that measles is a mild disease along the lines of the flu.

“The benefit of the vaccines has actually been kind of its own downfall,” according to Stanford Medical School epidemiologist Yvonne Maldonado. “People just don’t see this as a relevant intervention.”

In fact, measles can lead to serious complications. While some can be deadly, others can cause long-term damage that may not be captured by statistics on direct fatalities from measles. Roughly one in every 1,000 children that develop measles will suffer from encephalitis, a swelling of the brain, which can cause convulsions, deafness, or intellectual disability. One in 20 children that contract measles will develop pneumonia, which can itself be deadly. Young, unvaccinated children are at the highest risk for these complications.

Scientists are still unraveling the way measles operates in the body, and recently have uncovered another danger that may be easily missed in statistics about the disease. Measles has been known to target the immune cells, and scientists had been puzzled as to why. Recent research by Erasmus University Medical Center virologist Rik de Swart sheds light on this question, and emphasizes how the danger of measles goes beyond the most straightforward data.

The team found that the measles virus targets immune memory cells, which record infections throughout a person’s life to help fight them off in the future. When it infects these memory cells, the virus both eliminates some of these records and turns the immune system against itself, forcing it to kill off many of the immune memory cells are left.

This is part of why secondary diseases are so common with measles. It causes a kind of immune system ‘amnesia’ that can apparently last for years, making patients more vulnerable to other diseases. Researchers found that when widespread vaccination began in the 1960s, there were precipitous declines in overall rates of childhood disease. In unvaccinated populations, they found that half of all childhood deaths from infectious disease could be explained by infections that followed measles. They found that the best predictor of non-measles deaths was the number of measles cases over the preceding three years.

In countries like the US, healthcare systems will often (but not always) be able to prevent these complications from becoming fatal. But the WHO is now concerned that anti-vaccine sentiment could spread to densely populated nations with less accessible healthcare systems, such as Brazil, China, India, Indonesia, or Nigeria. Since young children are most vulnerable, including those that are too young to be vaccinated, this “vaccine hesitancy” puts whole populations at risk. As a result, the WHO ranked it alongside Ebola and influenza in the top ten world health threats for 2019.

What many don’t understand is that vaccination is not just a personal choice, it’s something that communities must manage as a whole. And as often as the question of compulsory vaccination may arise these days, the real question is how access to vaccinations came to be seen as anything less than a privilege.

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