Results from studies of more than 20,000 females have strengthened the case for young women and girls to be vaccinated against the virus that causes cervical cancer.
The combined results of four similar trials around the world show that for girls who have never had sex, the vaccines are 99% effective.
When the data from women who may have already been exposed to the sexually transmitted virus is included, effectiveness falls to 44%.
Currently there are two rival vaccines against the human papillomavirus (HPV) linked to cervical cancer.
One, Gardasil, is now licensed in the UK but is not yet officially available on the NHS. The other, Cervarix, has so far only been approved in Australia.
The Future II series of trials studied 20,583 women aged between 15 and 26 from North and South America, Europe, Asia and the Pacific.
Around 9,000 were given a course of Gardasil jabs, which protect against the two strains of HPV responsible for most cases of cervical cancer.
Another 12,000 received a component of the vaccine, and the remainder were administered with a placebo.
Only healthy women with no record of abnormal cervical smears and a history of less than five sexual partners were eligible.
Results from the trials were collated by a team led by Dr Kevin Ault, from Emory University School of Medicine in Atlanta, and have been published in The Lancet.
The researchers concluded: "The results of this... HPV vaccine programme provide strong evidence that implementation of HPV vaccination campaigns in preadolescent girls and young adult women will reduce rates of cervical cancer worldwide."
Your comments: It is time for all young women to be OFFERRED the vaccine, and the 15-26 age group sounds about right. 9 is far too young, either for the child to understand, or to expect parent to agree to a vaccination against what is essentially an STI - Laura, Leeds