MONTREAL - Issues like cost may mean a long wait before Canadian boys have the same access as girls to a public immunization program for a highly prevalent sexually transmitted disease, experts attending a conference on the subject said Saturday.

Publicly funded immunization for human papillomavirus has been offered to girls across the country for years, but boys have not had the same access.

"If we have a high coverage in girls we can also protect the boys because it's a sexually transmitted disease," said Marc Brisson, Canadian research chair in mathematical modelling at Laval University.

"In countries like Canada, it's not cost effective."

Brisson is among 1,700 specialists attending an international conference on HPV taking place in Montreal over the next few days.

The HPV is the most common sexually transmitted infection in the world, infecting an estimated 80 per cent of sexually active people globally.

HPV has been identified as being responsible for almost 100 per cent of cervical cancers -- the second most common among women between 20 and 44.

It's also associated with cancers of the anus, vulva, vagina, penis and throat as well as genital warts.

Health Canada approved the HPV vaccine for use by girls in 2006 and it's been part of school-based immunization campaigns across the country since 2008.

Last February, Health Canada also approved the use of the vaccine for boys.

But Brisson said provinces will be forced to weigh a number of factors before rolling out a public vaccination program for primary school boys.

"There's equity issues, cost effectiveness, public preferences and politics, all of these things," he said.

While vaccinating boys may be pricey, it may also help prevent a number of rare but increasingly prevalent cancers said Marc Steben, a medical adviser with the Quebec Institute of Public health and chair of the Montreal conference.

Steben said early Canadian studies suggest the vaccine offers 75 per cent protection against anal cancer.

About 90 per cent of anal cancers have been linked to the virus.

The HPV inoculation for Canadian males between nine and 26 is now being looked at by the National Advisory Committee on Immunization and the Canadian Immunization Committee to see if the target populations for the vaccine can be expanded.

The organizations will then make a recommendation on how inoculation programs should be implemented across Canada.

"Then it will be left for the provincial and territory governments to see if they will include it in their free programs," Steben said.

Parents can always choose to have their boys inoculated by purchasing the vaccine themselves.

But Steben believes the high rates of HPV infection may make it worthwhile despite the cost.

"It's so ubiquitous in terms of a virus," he said. "Four out of five people will be infected in their lifetime."

But Brisson questions remains whether governments should shell out for a pricey vaccine if the majority of Canadian girls have been given the inoculation.

"Vaccinating boys will be effective but it might not be the best use of our scarce resources," he said.