The bad rap — and the truth — about vaccinations

FOR more than a decade, a small but vocal faction of parents and health professionals have advocated the avoidance of childhood vaccinations in response to a perceived risk of autism and other health issues. Legislation being considered in Washington state would require parents who do not vaccinate their children to submit proof they've been informed of the risks and benefits of immunization. This raises the question: In a society that has all but eradicated many devastating and potentially lethal diseases, why are some individuals willing to risk their return?

The idea of a link between MMR vaccinations (against measles, mumps and rubella) and autism can be traced to two events.

First was the elimination of methyl mercury (thermisol) from vaccines as a precautionary measure by pharmaceutical companies. To some, this was perceived as admission a problem existed and a small number of people responded as such.

The second event was a United Kingdom study by Andrew Wakefield that was published in The Lancet in 1998. Wakefield's study drew links between MMR vaccinations and autism based on highly questionable data. In 2010, Wakefield was determined to have manipulated the study data as well as having acted unethically by the General Medical Council (the medical licensing authority in the UK). The Lancet paper was retracted and Wakefield was disbarred.

Today, the scientific consensus remains that no evidence exists to link the MMR vaccine to autism.

Yet anti-vaccination believers remain steadfast, unwilling to accept the preponderance of evidence contradicting their stance. Why?

Human beings are pattern finders. The nature of much of our intelligence is based on our ability to identify patterns in our environment. An animal slinking toward us on the savanna. The face of a friend in a crowd. The identification of seasonal weather patterns. Developing this ability gave us a tremendous advantage. It increased our chances of survival as individuals and as a species.

Unfortunately, this ability can also lead us to erroneous beliefs. The world is full of chaotic, random events, yet our drive to find patterns motivates us to give them form. We see faces in clouds. We believe in winning streaks at the roulette wheel. And sometimes, we find cause-and-effect relationships where none exist.

Millions of children receive immunizations every year. Some of these children will go on to be professional athletes. Others will become doctors. And unfortunately, some will develop autism. But this doesn't mean there is a causal link between any of these and being vaccinated.

Given a large enough statistical sampling, any number of correlative relationships are possible. This is why it's important to distinguish between causation and correlation. Or to put it another way: Correlation sees every pattern. Causation sees the correct pattern.

Then why are autism cases on the rise, anti-vaccine proponents often ask? Autism diagnosis is based on behavior rather than cause. In recent years, a broadening of the definition of autism to encompass a number of autism spectrum disorders may be the reason for the statistical jump. But even if autism really is on the increase, this doesn't mean the rise is being caused by vaccinations.

Confirmation bias goes a long way in keeping the myth of a vaccine-autism link alive. Proponents continue to seek out and share only information that supports their belief, disregarding scientific evidence or statistical analysis that contradicts their stance. The prevalence and public acceptance of conspiracy theories has skyrocketed with the growth of the Internet. Unfortunately, this has created fertile ground in which groups like the anti-vaccine movement can grow and persist.

The reason the aforementioned legislation is important is because a number of the diseases vaccinations protect against are on the rise. In 2006, there were 55 reported cases of measles in the entire U.S. The first six months of 2008 saw that number jump to 131 cases, of which 91 percent were unvaccinated. In 2010, whooping-cough deaths in California leapt to a 60-year high.

This isn't just a question of individual choice. Because of the way pathogens are transmitted within a population, achieving a high rate of immunization leads to something referred to as "herd immunity." Notice in the 2008 measles number that 9 percent of the infected were vaccinated (though some had not received their second dose.) While no vaccine will protect 100 percent of the population, it's safe to assume far fewer would have been infected if vaccination rates were higher.

Vaccinations are one of the major health achievements of the 20th century. Without them, our citizens would still be ravaged by smallpox, polio, tuberculosis and many other terrible diseases. The decision to try to educate people about the correct risks and benefits of immunization is a wise step in the right direction. Ultimately, the decision to vaccinate becomes not just a question of personal responsibility, but of social responsibility as well.