Libertarian presidential candidate Gary Johnson has apparently had a change of heart with regard to requiring childhood vaccinations. In my earlier evaluation of Johnson's stands on various science policy issues, I reported that I could "find no statements from Johnson suggesting that he thinks that vaccination might cause autism. In 2015, Our America Initiative, a non-profit co-founded by Gary Johnson, announced that it supported a Mississippi advocacy group's effort to place "childhood vaccination decisions into the hands of parents and doctors." I gave Johnson a "PASS" based on the fact that he hadn't fallen for the scientifically false claim that vaccination causes autism.

Now, according to Vermont Public Radio, Johnson has rethought his views on mandatory vaccination. Johnson says in the interview:

I've come to find out that without mandatory vaccines, the vaccines that would in fact be issued would not be effective," he said. "So … it's dependent that you have mandatory vaccines so that every child is immune. Otherwise, not all children will be immune even though they receive a vaccine." Johnson said he believes vaccination policy should be handled at the local level. "In my opinion, this is a local issue. If it ends up to be a federal issue, I would come down on the side of science and I would probably require that vaccine," he said. Johnson said his position changed recently. "It's an evolution actually just in the last few months, just in the last month or so," he said. "I was under the belief that … 'Why require a vaccine? If I don't want my child to have a vaccine and you want yours to, let yours have the vaccine and they'll be immune.' Well, it turns out that that's not the case, and it may sound terribly uninformed on my part, but I didn't realize that."

Good for him. Johnson clearly recognizes that vaccinations safely protect people from diseases. In addition, he has now come to recognize the importance of herd immunity for protecting vulnerable people who are too young to be vaccinated, whose vaccinations have failed to take, and those whose immune systems are compromised.

For more background, see my article, "Refusing Vaccination Puts Others Risk," in which I explain that there is no principled libertarian case for free-riders to refuse to take responsibility for their own microbes.

For a broader debate, see "Should Vaccines Be Mandatory?"