The recommended dosage schedule is three doses, but a new study is now looking at whether two doses given at a younger age might still be effective.
"It's traditional with these protein vaccines to give two doses quite close together within a couple of months of each other and then wait a period of time and give a third dose," said Dr. Simon Dobson, University of British Columbia.
Dr. Dobson and co-authors looked at whether young girls aged 9 to 13 who received two doses of the vaccine would be just as protected as young women 16 to 26 who received the recommended three-dose vaccine.
"The two doses given to young girls was no worse than the three doses given to young women. At least immediately after the last dose had been given, the responses in the two-dose girls was no worse than the three-dose girls," said Dobson.
The study appears in the Journal of the American Medical Association.
"Two doses in girls is certainly enough to start with but it doesn't answer the question whether that's going to be enough to get women through the peak young-adult years when they are most likely to meet HPV," said Dobson.
Researchers say the immune response in young girls is still unknown. Further studies may indicate a third booster may be needed when the girls get older. But since the vaccine is expensive, giving two doses instead of three may encourage more use of the vaccine around the world.
The bottom line: While it would encourage more girls to get the HPV vaccine at just two doses instead of three, researchers say there's not enough information yet to recommend it.