Miami Children's Hospital pediatrician Dr. Amanda Porro, M.D administers a measles vaccination to Sophie Barquin,4, as her mother Gabrielle Barquin holds her during a visit to the Miami Children's Hospital on January 28, 2015 in Miami, Florida. (Photo by Joe Raedle/Getty Images)

Polling has suggested as many as three in 10 Americans think that vaccines should not generally be mandatory. And while that's a key political question, it doesn't really get at the heart of the matter: just how many Americans are so-called "anti-vaxxers," i.e. think vaccines are actually harmful.

The answer, at least when it comes to the measles vaccine, is 9 percent, according to a new poll.

The survey from the Pew Research Center shows 83 percent of Americans think the measles vaccine is safe, while 9 percent think it's not. Another 7 percent are not sure.

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As with the vaccine choice question, these anti-vaxxers skew toward younger and less-educated Americans, along with racial minorities. Contrary to some conventional wisdom, though, they disproportionately come from places other than the West, where 90 percent see the vaccine as safe.

The poll also shows more Democrats (9 percent) and independents (10 percent) say the measles vaccine isn't safe than Republicans who say the same (5 percent). These differences are well within the margin of error, but the aforementioned Pew poll showed Republicans were more likely than Democrats to say vaccines should be a matter of choice.

Of course, practically speaking, vaccine skeptics carry more weight than the 9 percent suggests. That's because, among people who are actually parents of minors, the number is slightly higher: 13 percent.

In fact, only 80 percent of such parents are sure that the measles vaccine is safe. Which could say a lot about why we find ourselves in the situation we do.

Of course, with all of this, you need to keep in mind that skepticism about other vaccines could be different. The measles vaccine, though, is the one erroneously linked to autism in a now-discredited 1990s study.