A head and neck surgeon in Saskatoon says vaccinating children for the human papillomavirus is about cancer, not sex.

Dr. Peter Spafford was reacting to a letter signed by Catholic bishops and sent to parents of children who attend separate schools in the province earlier this week.

"The medical message is that the vaccine is about preventing disease and cancer and it's not really about sex, per se," Spafford said.

"We actually have a vaccine that could potentially protect [against] cancer 100 per cent," Spafford said.

There are more than 100 different types of HPV, but according to the Canadian Cancer Society, the majority of HPV-related cancers are caused by two types that are almost entirely preventable through vaccination.

Dr. Peter Spafford

Dr. Peter Spafford says for doctors, the HPV vaccine is about preventing cancer. (Rosalie Woloski/CBC)

The vaccine has been offered to Grade 6 girls in Saskatchewan since 2008, but this is the first year it is being offered free of charge to boys.

Spafford said that is due to the "astronomical" rise in cases of throat cancer in men. 

"It's gone up 56 per cent in the last 20 years," Spafford told CBC Radio's The Morning Edition host Sheila Coles on Thursday.

"In the cancer world, that's alarming."

Spafford said while doctors do believe in other forms of protection, including condom use and abstinence from sexual intercourse, those are not a guarantee against contracting this virus.

"Almost all types of sexual activity can lead to HPV transmission — for example oral sex, any skin to mucosa contact, any contact even with skin and body fluids can do it," he said.

Spafford said about 75 or 80 per cent of Canadians will contract the HPV virus if not vaccinated.

"Most HPV infections come and go over the course of a few years," the Cancer Society says.

'Strong moral implications,' say bishops

The decision to vaccinate children is "a serious health decision with strong moral implications," the letter to Catholic parents reads. 

It cautions that before allowing their children to receive the shots, parents should consider whether vaccinating for HPV will encourage risky sexual behaviour.

Medical experts say the research shows no increase in sexual activity by girls who have had the vaccine.

"There is absolutely no change in sexual behaviours," said Dr. Saqib Shahab, the province's chief medical health officer.

What there has been, he said, is a "marked reduction in early cancerous lesions that are due to HPV that are prevented by the vaccine."

Shahab said the vaccine has been shown to be safe and effective and the province recommends all Grade 6 children receive it.

With files from The Morning Edition