A 2013 study found that the biggest contributor to distrusting or disliking vaccines was not political ideology, but having a conspiratorial mindset, which can occur on both the left and the right. Those who mistrust vaccines claim that childhood vaccinations can cause autism.

Republican Gov. Chris Christie of New Jersey said Feb. 2 that parents “need to have some measure of choice in deciding whether or not to vaccinate their children. Christie clarified his original comment later that day, claiming “different states require different degrees of variation,” and “balance” is key.

President Obama on Feb. 1 urged parents to vaccinate their children, telling NBC that the scientific rationale for using vaccines is “pretty indisputable.” In recent weeks, a measles outbreak linked to Disneyland in California has spread to over 100 people.