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The controversy about autism and vaccines is back in the news again, as Jenny McCarthy has taken a job with ABC’s The View. People want to see her blackballed. It’s an interesting coincidence that this issue should return the same week that twenty-three children in India died, and many others sickened by poison from school lunches that were supposed to be safe. I wonder if the Indian government will undertake studies now to determine whether a causal link exists between school lunches and fatal food poisoning.

Here’s an article on the subject. It dates from 2011, when the press pilloried Andrew Wakefield every time you looked up from your coffee. See also this web page titled Informed Choice: MMR vaccine and the autism epidemic. I don’t want to travel back to that controversy at the moment. Instead, let me propose a thought experiment that tries to capture the way people deal with the uncertainty of long odds.

Suppose we estimate that one bad batch of vaccine — with odds of harm far lower than one bad batch of school lunches — could cause autism in one child for every billion vaccines administered. These odds are lower than one’s chance of winning the Powerball lottery. We know the odds of winning that lottery are almost nil. Yet who, if handed a gun with a billion chambers in it and one bullet, would hold it to his head and pull the trigger? Who would do it even if you were offered a Powerball jackpot as an incentive? I suppose a number of people would think about that one, but I wouldn’t do it.

Now let’s refashion the thought experiment to bring it closer to a scenario for a bad batch of vaccines. Suppose someone hands you a gun with a billion chambers. One chamber might have a bullet in it. The gun owner says that you and 999,999,999 other people are going to play Russian roulette. The game will prevent some substantial but indeterminate number of people from getting sick, but one person may have to take a bullet to achieve this outcome. How many people would want to play that game? More to the point, how many people would force their children to play that game?

Note a few characteristics of this experiment. First, a statistical study designed to determine whether a relationship exists between playing the game and untimely death by gunshot would not find a relationship. The odds are too long and the causes of death too variable. Among a billion people, some number will use a gun to end their lives intentionally, and others will die of accidental gunshots, whether or not they play the game. No statistician, no matter how well the study is designed, could establish a relationship between playing the game and sudden death from a gunshot wound to the head.

Second, the experiment suggests that people deal rationally with long odds. People know that chances of winning the lottery are extremely small, but they play the game anyway because they enjoy it. Similarly, no rational person would want to risk even a small chance of death to help keep other people from becoming sick. That goes double for your children. People want to help others, but not if even a tiny chance exists of bringing harm to your son or daughter.

Third, people do not take these decisions in isolation. Even among a billion people, those who play the game communicate with each other. They can find out if someone’s child died or became sick. Parents can share their stories. These stories do not depend on Andrew Wakefield or Jenny McCarthy to spread. The internet hosts many, many forums for parents of autistic children. The stories that suggest a possible link between vaccines and autism do not cause hysteria. They cause parents to make rational calculations about long odds.

I have a special interest this question, because my brother-in-law suffered from the same sequence of events that Jenny McCarthy’s son did. It happened in the late 1950s, before we even knew what autism was. When Ms. McCarthy found herself facing a doctor ready to vaccinate her son, she said, “This is the autism vaccine, isn’t it?” The doctor assured her that her son would be all right. He was not all right. A normal, bright boy became autistic. Why would you blame Ms. McCarthy for telling her story to others?

A similar sequence occurred around the time my brother-in-law reached the age of three, in 1960. According to a family friend, nothing was wrong with him during the early years of his life. Then he suffered a seizure. He never recovered from it. He remained severely autistic for the rest of his life. People at the time could not distinguish autism from mental retardation. People at the time certainly did not know what would cause a condition like that. We still don’t know what causes autism. We also don’t know what caused my brother-in-law’s seizure.

If we do not know what causes autism, we cannot rule tainted medications in, or out. Because we do not know how the brain’s cognitive, communicative, social and neural functions develop or go awry, we do not know by what mechanism thimerosal or any other ingredient in vaccines might cause harm. Thimerosal is a vaccine preservative that contains mercury. Drug companies use it to keep vaccines fresh until they reach their destination. They assure us the vaccines are safe, because the amount of preservative is so small.

The drug compounding company in Framingham, Massachusetts, responsible for a huge outbreak of fungal meningitis also assured its customers that the steroids it sold were safe. The Food and Drug Administration approved its operations. If asked, the people who supply ingredients for school children’s lunches in India would assure you that their products are safe, too.

Assurances of safety cannot possibly prevent someone making a mistake that results in too much thimerosal in a vaccine. Statistical studies that test for a correlation cannot possibly control for, detect, or prevent such mistakes.  The people in Framingham and in India made mistakes that caused people to die. We know of other cases, such as distribution of tainted baby formula in China, where babies suffered grievous harm. To pillory Andrew Wakefield, Jenny McCarthy, or anyone else for raising this issue of bad vaccines is nothing more than a concentrated social effort to suppress free speech.

The people who seem to hate Wakefield and McCarthy so much should ask themselves, would they put a billion-chamber gun that might have one bullet to their child’s head, and pull the trigger? Social pressure, no matter what the perceived benefits for prevention of illness, should never force a parent who is anxious about the effects of a vaccine to have it administered. If the principle of individual choice holds anywhere, it holds here.