The U.S. Centers for Disease Control and Prevention has suggested that parents have their middle-school-aged daughters vaccinated against a sexually transmitted disease closely linked to cervical cancer.

The human papillomavirus is the most common STD, according to the Centers for Disease Control and Prevention, and the second leading cause of female cancer mortality worldwide, according to the World Health Organization. There are currently two FDA-approved vaccines - Gardasil and Cervarix - to protect against the types of HPV that cause most cervical cancers. While each vaccine uses different substances to rev up the immune system, both are given as shots and must be received in three doses over a six-month period, according to the manufacturers.

That's nothing new.

1. So, why is there such a debate swirling around the issue? Well, politics.

You've probably seen headlines about the HPV vaccine for years now, so what's new? A bigger spotlight, essentially, and the vaccine has come up amid jockeying for the GOP presidential nomination.

The debate over the use of the HPV vaccine - and specifically how it is given and who can mandate it - became a hot topic after some tense exchanges during Monday’s CNN/Tea Party GOP debate.

GOP presidential contender Rep. Michele Bachmann challenged one of her rivals for the Republican nomination, Texas Gov. Rick Perry, on his 2007 executive order that would have required Texas schoolgirls to receive vaccinations against HPV. Bachmann suggested the governor acted for political reasons, noting that the maker of Gardasil - the only Food and Drug Administration-approved HPV vaccine at the time – contributed to his campaigns, and that his former chief of staff lobbies for the company. She also said the drugmaker, Merck & Co., stood to make millions of dollars because of the order.

Truth Squad: Was Bachmann's claim about Perry's mandate for political reasons true?

Bachmann’s challenge came as candidates discussed the pros and cons of executive orders, and when and how the president should use one.

Perry said during the debate that if he could do it over again, he wouldn’t use an executive order, but would work with the legislature.

2. OK, wait. What actually happened in Texas?

Since 2006, 19 state legislatures have attempted to pass legislation that would mandate HPV shots for school, after the CDC recommended that parents be advised that the shot was a good idea and a way of preventing cervical cancer.

Perry took that one step further. In February 2007, he signed an executive order directing the state Health and Human Services commissioner to mandate HPV vaccinations for all girls before admission to the sixth grade. Perry at the time released a statement saying that the vaccine "provides us with an incredible opportunity to effectively target and prevent cervical cancer.”

Texas' rules were to take effect in September 2008. However, the Texas Legislature passed a bill overturning Perry's order in April 2007. Perry declined to veto the bill, which went into effect in May 2007, killing his order.

3. Politics aside, what are the health concerns?

We've been vaccinating kids - by mandate - for school for years. And for all of those vaccines, parents have the ability to opt out. Again, that's nothing new.

But public perception is changing.

The debate over vaccinations picked up steam after concerns and arguments over whether childhood vaccinations were linked to autism or other diseases became another hot topic. Some were quick to warn of harmful side effects. And then, some medical journals retracted studies linking the two.

Many advocates against vaccinations still said that not enough was known and stood by the idea that there was a connection.

During Monday’s debate, much of the brouhaha over the HPV vaccine centered more on how Perry approached the issue than the vaccine itself. After the debate, Bachmann did touch on whether the vaccine was safe: She said parents told her that the vaccine had made their children sick.

But when it comes to the HPV vaccine, the CDC breaks it down pretty easy: It is safe and can go a long way in preventing a deadly cancer. The CDC says studies of the vaccine "showed no serious side effects," but "common, mild side effects included pain where the shot was given, fever, headache, and nausea." The CDC has said that if you get sick after the shot, it's a coincidence, not cause and effect, CNN's Senior Medical Correspondent Elizabeth Cohen reports.

Then there's the issue about the age of vaccination.

Middle school children are the targets of the vaccine, and there are some concerns about whether they should be vaccinated at an age when many may not be sexually active. And in some conservative areas, there is concern that the vaccine might encourage children to have sex at an earlier age.

4. So what do the vaccines do?

The FDA has licensed two HPV vaccines recommended by the CDC: Cervarix and Gardasil.

So what are the similarities? According to the CDC:

■ Both vaccines are very effective against HPV types 16 and 18, which cause most cervical cancers. So both vaccines prevent cervical cancer in women.

■ Both are very safe.

■ Both are made with very small parts of the human papillomavirus (HPV) that cannot cause infection

■ Both are given as shots and require three doses.

And what are the differences? According to the CDC:

■ Only one of the vaccines (Gardasil) protects against HPV types 6 and 11 - the types that cause most genital warts in females and males.

■ Only Gardasil has been tested and licensed for use in males.

■ Only Gardasil has been tested and shown to protect against cancers of the vulva, vagina and anus.

■ The vaccines have different adjuvants, substances that are added to increase the body's immune response.

(You can read more about HPV and the vaccines from the CDC here.)

5. Where do things currently stand across the country with regard to the vaccine?

Of the 19 states that tried to pass legislation mandating vaccination for children to attend school, only two passed the legislation. (You can see a full list of the attempted bills in each state here.)

Only Virginia and Washington, D.C., have passed measures to require the mandate. In Virginia, the legislature tried to reverse the mandate. The state's House passed the reversal, but the bill was killed in a Senate committee, so the mandate still stands.

Even there, where this is a mandate, it appears that more families are choosing to opt out of the program than to take part in it.

"Just 17.3 percent of eligible girls had received the first of three vaccinations, as envisioned by the law, at the start of this school year," according to Rosalind S. Helderman, writing for The Washington Post in February. "Only 23 percent of this year's eligible sixth-graders in the District have received the vaccine."