Pharma companies Merck and GSK are squaring up for a fight, with rival products vying for a slice of the controversial cervical cancer vaccine market.

Merck’s Gardasil has already been on the market for a while, and the company last week unveiled results showing that it can protect for over eight years, extending the known protection time.

GSK meanwhile unveiled a study on its product Cervarix, which it claims shows it to be better than Gardasil. Cervarix has yet to be approved by the US Food and Drug Administration, although it is used in other countries.

The whole issue of vaccinating against cervical cancer has been controversial. Both Merck and GSK’s vaccines actually protect against Human papillomavirus (HPV) , which can cause the cancer. Some groups, mainly on the political right, fear that vaccinating young people against STDs may encourage promiscuity, although the US Centres for Disease Control recommends vaccination for all 11 and 12 year old girls.

According to the Wall Street Journal, $1.4 billion of Gardasil sold last year, while GSK moved about $231 million-worth of Cervarix. As Mike Huckman notes on MSNBC’s Pharma’s Market blog, which vaccine works best is only one part of the fight.

“Sales of Gardasil are going down,” he writes. “By its own admission, Merck is having a tough time getting females in their late teens and early- to mid-20s to get the set of three shots.

“It’s hoping to find a way to break through with that population and to win approval of the vaccine for older women and males to reignite sales growth. And Glaxo will be late getting into the game.”