A new Canadian study offers some hope that two doses of HPV vaccines may work as well as the current regimen of three.

In recent years two new vaccines have come into the market that protect against human papillomaviruses which cause cervical cancer,head and neck cancers and some other urogenital cancers.

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It's not yet clear how long the protection of two doses of HPV vaccination will last. (Joe Raedle/Getty )

But the vaccines are given in three doses and are expensive, costing between $400 and $500 per child.

All Canadian provinces and territories currently offer the vaccine for free to girls, but there have been calls to widen the programs to include boys as well.

A new Canadian study looks at whether the dosing schedule could be changed to drop one of the shots — a move that would save substantial amounts of money.

It suggests that two doses in pre-adolescent girls works as well as three doses in girls in their later teens and early 20s, but says more study is needed.

The lead author, Dr. Simon Dobson of the University of British Columbia in Vancouver, says it's still not clear how long the protection of two doses will last and whether another booster shot would be required down the road.

In the study, 520 girls aged nine to 13 were randomly assigned to receive two doses or three.

The vaccine used in the study was Gardasil, which is made by Merck Canada. It protects against two strains of HPV that cause cancer and two that cause genital warts.

Another vaccine, Cervarix, protects against the two cancer-causing strains. Cervarix is made by GlaxoSmithKline. Other studies that looked at Cervarix have found similar results to the question of whether two doses might be sufficient.

The new study is being published in the Journal of the American Medical Association.