The Complicated Truth About Vaccines

They can appear to be the proximate cause of a condition when they have nothing to do with the ultimate cause.

By Michael Segal

Why are people afraid of vaccines? The already strong evidence of their safety got stronger in March with the release of a large Danish study that addressed several objections to previous studies and found that the measles vaccine poses no additional risk of developing autism.

Yet the Centers for Disease Control and Prevention reported April 26 that there have been 704 cases of measles so far this year. “The suffering we are seeing today is completely avoidable,” Health and Human Services Secretary Alex Azar said Monday. “We know vaccines are safe because they’re among some of the most studied medical products we have.”

So why does skepticism persist? One reason is that scientists, physicians and journalists are overly dismissive of the observations that circulate among the public. In a 2015 presidential debate, Donald Trump said an employee had a 2-year-old daughter who “went to have the vaccine and came back and a week later got a tremendous fever, got very, very sick, now is autistic.” Media commentaries accused Mr. Trump of trafficking in conspiracy theories. But what if his account was true?

It was anecdotal, and experts know the plural of “anecdote” isn’t data. Science advances by collecting and analyzing data in rigorous and meaningful ways. A study led by neurologist Samuel Berkovic applied that approach to vaccine reactions, and the results provide a model for understanding and overcoming skepticism about the safety of vaccines.

Dr. Berkovic and his colleagues studied a genetic form of epilepsy caused by mutations in the SCN1A gene, a DNA sequence that specifies part of a channel in nerve-cell membranes that allows sodium ions to enter the cell. Children born with such SCN1A mutations are destined to develop seizures and regress neurologically. The researchers found that the onset of these seizures peaked in the days after vaccination but then dipped below baseline in subsequent weeks. The net result was that vaccines had no effect on the likelihood of developing the inevitable deterioration from these mutations.

That is, vaccines did trigger the deterioration—but had the children not been vaccinated, the same deterioration would have occurred anyway the next time they had a cold. These results are fully consistent with the large-population studies. But by studying the detailed time course in a genetically characterized population, they illustrated how vaccines can appear to be the proximate cause of an injury, yet the ultimate cause is genetic.

When parents ask me about vaccines, I inspire confidence by telling them that my three kids got all the recommended vaccinations on schedule. But when dealing with public policy about mandatory vaccinations, one needs to address the elephant in the room: the stories of deterioration following vaccinations. Many experts prefer to ignore such anecdotes, and when engaged in public debate, find it hard to resist the ethos of an advocate—pushing the conclusion but playing down the complexity. That’s been counterproductive. People hear stories about neurological deteriorations and trust their friends more than the experts. Unless we act like scientists and explain the science, we won’t be effective in helping laymen put the anecdotes in context.

Someday we may identify newborns at risk for genetically determined neurological deteriorations and intervene, preventing the fever and inflammation from colds and vaccinations from triggering deterioration. We don’t yet know how to do that, and people should follow recommendations to get vaccinated. Vaccinations don’t make these genetic susceptibilities worse, and they prevent the contagions that used to kill thousands a year.

If you remain unvaccinated, you run the risk of getting infected as an adult, when diseases like chickenpox and measles are far likelier to be fatal. If you become infected, you also risk the lives of others who are most vulnerable to infection.

Dr. Segal is a neurologist and neuroscientist who studies diseases of ion channels.

Appeared in the May 2, 2019, print edition of the Wall Street Journal.

Copyright© 2019 Michael Segal.