More countries are dropping the number of doses needed for HPV vaccines. Should Canada?

Starting this fall, teens in England will get just one HPV shot — making it the latest country to drop the number of required doses for the highly-effective vaccines known for protecting against a slate of cancers.

The World Health Organization (WHO) announced more than a year ago that a single dose delivers "solid protection" against human papillomavirus (HPV) that's comparable to two or three shots, based on a growing body of global evidence. Ireland, Scotland, Wales, and Australia have already made the switch. And many researchers say providing fewer doses can free up much-needed resources for other public health efforts.

So, should Canada follow other countries' lead by taking a one-dose approach? There's no decision here just yet.

The country's top vaccination advisors are looking at "all the available evidence" while conducting their own analysis based on Canadian disease rates and modelling projections, a spokesperson for the Public Health Agency of Canada told CBC News. That work is "expected to be finalized next year."

Currently, Canadian guidelines suggest that healthy kids aged nine to 15 should get one of the available HPV vaccines on either a two or three-dose schedule. 

The current chair of Quebec's immunization committee, Dr. Caroline Quach — who chaired NACI during much of the COVID-19 pandemic — is among the Canadian medical experts who say Canada should consider following the lead of England and other countries.

"When you look at the studies that have been published worldwide… the effectiveness of one dose of the HPV vaccine is actually quite high," Quach said. 

"In terms of prevention of HPV infections that may lead to cancer, whether you give one dose or two doses basically gives you the same amount of protection."

Research from India and Costa Rica has shown the durability of one dose of certain types of HPV vaccines lasts a decade, noted the U.K.'s vaccine advisory committee.

The U.K. also looked at a more recent trial in Kenya, which was also meant to study the effectiveness of a single dose. That research found young girls and women were effectively protected from HPV infection for 18 months post-vaccination — with vaccine efficacy at more than 97 per cent, keeping the results in line with trials for three doses.

"Every country and every advisory committee needs to review the data and look at the modeling, the epidemiology of their own country," noted Quach. "But it's absolutely something that we have to look at."

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Dawn Bowdish, an immunologist from McMaster University in Hamilton, Ont., said she feels a cautious approach is more prudent, to gauge whether a reduced number of required doses maintains decades-long protection.

Most childhood vaccines need multiple doses to sufficiently train the immune system to recognize a threat long-term,  she added. And even with less HPV circulating now in Canada thanks to years of HPV vaccination efforts, she said the country remains in a "delicate spot."