To the extent that science understands them, a few important things: 

• 12,357 women in the United States were diagnosed with cervical cancer in 2009, and 3,909 died of it. 
• Most cervical cancer is caused by human papillomavirus (HPV). 
• In 2006, the FDA approved a vaccination against HPV that can prevent some of said cervical cancer. 
• The CDC and American Academy of Pediatrics recommend the vaccine to all teenagers. No studies have proven or raised serious questions about any associated side effects.

Despite all that 75 percent of teenage girls in the U.S. were, as of 2010, not up to date on their HPV vaccinations. That number is highlighted in an analysis by Dr. Paul Darden and colleagues in Monday's edition of the journal Pediatrics. 

What's more, 44 percent of parents said they didn't plan to get their daughters vaccinated, which was up from 40 percent two years earlier. 

Darden concluded, "Despite doctors increasingly recommending adolescent vaccines, parents increasingly intend not to vaccinate female teens with [the] HPV [vaccine]." 

Amid the anti-vaccination mania by which historians may well define this era, the growing reluctance and some of its justifications uncovered by Darden were unique to the HPV vaccine. Here are the reasons given by parents in 2010:

The 14 percent who answered "not sexually active" highlight the misconception that people who are not having sex don't need the vaccination. It's most effective when given before a person starts having sex. There's also the misconception here that parents actually know when their kids start having sex.

The 16.4 percent that cited safety concerns was striking, since the number tripled between 2008 and 2010. Unfortunately the subjects didn't expand on what those concerns were or what prompted the rise. 

And then, the "not needed/not necessary" responses ... see the mortality statistics above. 

In the U.K., a British National Health service program lets teenagers get the vaccine without parental consent. They have even incentivized it with shopping vouchers. 

In the U.S., only 45 percent of adults said they would be in favor of allowing teenagers to get vaccinated without parental consent. Though clearly sometimes parents just don't understand.