One-Dose HPV Vaccine Program Would Be Efficient in Canada

In Canada, switching to a one-dose, gender-neutral vaccination program for human papillomavirus (HPV) could use vaccine doses more efficiently and prevent a similar number of cervical cancer cases, compared with a two-dose program, according to a new modeling analysis.

If vaccine protection remains high during the ages of peak sexual activity, all one-dose vaccination options are projected to be “substantially more efficient” than two-dose programs, even in the most pessimistic scenarios, the study authors wrote.

In addition, the scenarios projected the elimination of cervical cancer in Canada between 2032 and 2040. HPV can also lead to oral, throat, and penile cancers, and most are preventable through vaccination.

“The COVID-19 pandemic has impacted HPV vaccination in Canada, particularly among vulnerable population subgroups,” said study author Chantal Sauvageau, MD, a consultant in infectious diseases at the National Institute of Public Health of Quebec and associate professor of social and preventive medicine at the University of Laval in Quebec City, Quebec, Canada.

Switching to one-dose vaccination would offer potential economic savings and programmatic flexibility, she added. The change also could enable investments aimed at increasing vaccination rates in regions where coverage is suboptimal, as well as in subgroups with a high HPV burden. Such initiatives could mitigate the pandemic’s impact on health programs and reduce inequalities, said Sauvageau.

The study was published online on October 7 in CMAJ.

Vaccination Program Changes

Globally, countries have been investigating whether to shift from a two-dose to a one-dose HPV vaccine strategy since the World Health Organization’s Strategic Advisory Group of Experts on Immunization issued a single-dose recommendation in 2022.

In July, Canada’s National Advisory Committee on Immunization (NACI) updated its guidelines to recommend the single-dose approach for ages 9-20 years. The change aligns Canada with 35 other countries, including Australia and the United Kingdom. Canada’s vaccine advisory group still recommends two doses for ages 21-26 years and three doses for patients who are immunocompromised or have HIV.

To help inform new NACI policies, Sauvageau and colleagues modeled several one-dose and two-dose strategies using HPV-ADVISE, an individual-based transmission-dynamic model of HPV infections and diseases. They looked at vaccination programs in Quebec, which has a high HPV vaccine coverage rate of around 85%, and Ontario, which has lower coverage of around 65%.

For one-dose programs, the researchers analyzed noninferior (98% efficacy) and pessimistic (90% efficacy) scenarios and different average vaccine duration periods, including lifelong, 30-year, and 25-year coverage. They compared the scenarios with a two-dose program with 98% efficacy and lifelong duration, estimating the relative reduction in HPV-16 infection and cervical cancer incidence and the number of doses needed to prevent one cervical cancer case.

Overall, the model projected that gender-neutral HPV vaccine programs with either two doses or a noninferior one dose would nearly eliminate HPV-16 infection by 2040-2045 in Quebec and reduce infection by more than 90% in Ontario. Under a one-dose strategy with 90% vaccine efficacy, rebounds in HPV-16 infection would start more than 25-30 years after a switch to a lower-dose strategy, thus providing time for officials to detect any signs of waning efficacy and change policies, if needed, the authors wrote.

In addition, the model projected that a noninferior one-dose, gender-neutral HPV vaccination program would avert a similar number of cervical cancer cases, compared with a two-dose program. The reduction would be about 60% in Quebec and 55% in Ontario compared with no vaccination. Under the most pessimistic scenario with 25-year vaccine duration, a one-dose program would be slightly less effective in averting cancer: About 3% lower than a two-dose program over 100 years.

All one-dose scenarios were projected to lead to the elimination of cervical cancer in 8-16 years — at fewer than four cervical cancer cases per 100,000 female-years.

One-dose programs would also lead to more efficient use of vaccine doses, with about 800-1000 doses needed to prevent one cervical cancer case in a one-dose program and more than 10,000 incremental doses needed to prevent one additional cervical cancer case in a two-dose program.

What Next?

In Canada, the HPV vaccine is authorized for patients aged 9-45 years. Current immunization coverage among adolescents and young adults varies across provinces and falls below the national target of 90%. In its July 2024 update, NACI estimated that 76% of 14-year-olds of both genders received at least one vaccine dose and that 67% received two doses in 2023. Vaccine uptake was slightly higher among girls than boys.

To boost the coverage rate, shifting to a one-dose schedule could appeal to young people, as well as maintain vaccination efficacy.

“When you look at the studies that have been published worldwide, the effectiveness of one dose of the HPV vaccine is actually quite high,” said Caroline Quach-Thanh, MD, professor of microbiology, infectious diseases, immunology, and pediatrics at the University of Montreal, Montreal, Quebec, Canada.

Quach-Thanh, who wasn’t involved with this study, previously served as NACI chair and now serves as chair of the Quebec Immunization Committee.

“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,” she said.

However, not all physicians agree about the switch in vaccination approaches. In early October, the Federation of Medical Women of Canada released a report with 12 recommendations to increase HPV vaccination rates, including a call for healthcare providers to continue with multidose immunization schedules for now.

“Vaccination is the most powerful action we can take in preventing HPV-related cancers. Canada is falling behind, but we can get back on track if we act quickly,” said Vivien Brown, MD, chair of the group’s HPV Immunization Task Force, chair and cofounder of HPV Prevention Week in Canada, and a past president of the federation.

After the NACI update in July, the task force evaluated the risks and benefits of a single-dose vaccine regimen, she said. They concluded that a multidose schedule should continue at this time because of its proven effectiveness.

“Until more research on the efficacy of a single-dose schedule becomes available, healthcare providers and public health agencies should continue to offer patients a multidose schedule,” said Brown. “This is the only way to ensure individuals are protected against HPV infection and cancer over the long term.”

The study was supported by the Public Health Agency of Canada, the Canadian Institutes of Health Research, the Bill & Melinda Gates Foundation, and Canadian Immunization Research Network. Sauvageau, Quach-Thanh, and Brown declared no relevant financial disclosures.

Carolyn Crist is a health and medical journalist who reports on the latest studies for Medscape Medical News, MDedge, and WebMD.