Although Gardasil has been approved in males since 2009 and the vaccine has been gender-neutral for a decade, early marketing was heavily angled towards the prevention of cervical cancer, leading to more females to receive the vaccine than males. In recent times in the US, the rates of HPV vaccination have been more similar between males and females, and head and neck cancers have surpassed cervical cancer as the most prevalent HPV-related cancer types in the US.
“HPV vaccination has had a well-documented real-world impact on the precursors of cervical cancer,” said Karen Canfell, Professor in the school of public health at the University of Sydney and director of the cancer research division at the cancer council of New South Wales in Australia. “Countries with high rates of vaccine uptake have seen a rapid reduction in vaccine-included HPV type infections and reductions in cervical high-grade precancerous abnormalities,” said Dr Canfell.
HPV infection is thought to cause cancer only after a long latency period, meaning that people typically develop HPV-related cancers several years or even decades after initial infection with HPV. Hence, even for cervical cancer, dramatic drops in incidence have yet to be seen.
“Modeled analysis predicts that an impact on invasive cervical cancer incidence in young women (ie, those young enough to have been offered vaccination) should be evident in some countries very soon,” said Dr Canfell, noting that in Australia, which introduced HPV vaccination in 2017, it is predicted that a vaccine-associated reduction in cervical cancer incidence should be seen within a few years. Due to this latency between infection and carcinogenesis, it may be some time before the direct impact of the vaccine on head and neck cancer incidence can be determined.
“HPV vaccination is delivered to young adolescents and preadolescents, whereas the peak age of cancer risk is usually for people in the forties and fifties and older. Therefore, it will take several decades for adolescent HPV vaccination programs to realize their full effects in terms of cancer reductions,” said Dr Canfell.
Despite considerable increases in the number of males getting the HPV vaccine in the US in recent years, national rates are still not as high as many experts would like them to be. As of 2018, only 51% of teenagers aged 13 to 17 years had received all recommended doses of the vaccine.4 Will the new approval make any difference in the uptake of the vaccine?
“I don’t think this will change much from a patient perspective, but from a systems and research perspective, it is very important, as it changes the cost-benefit [calculation]. The vaccine is known to prevent 4 cancers and highly likely to prevent 6 cancers, which are thought to collectively be 5% of all cancers globally. That a vaccine can do this, is incredible,” said Dr Brewer.
The ultimate goal of many public health experts is to reach “herd immunity” status, meaning that the HPV strains in the vaccine simply do not get transmitted within the population and eventually become very rare. But many predict that at least 80% uptake in the population would be needed to reach that goal, and the US is still some way from achieving this, with growing anti-vaccine sentiment also presenting an additional challenge.
“Rates in the US are too low for every single state and every single subgroup – nobody is reaching 80% of their population vaccinated. Eradication isn’t on the table and we will never eliminate cervical cancer, but I do believe we can get pretty close to eliminating the HPV strains in the vaccine,” said Dr Brewer.
- Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc. FDA approves Merck’s Gardasil 9 for the prevention of certain HPV-related head and neck cancers [press release]. Published June 12, 2020. Accessed August 10, 2020. https://www.merck.com/news/fda-approves-mercks-gardasil-9-for-the-prevention-of-certain-hpv-related-head-and-neck-cancers/
- US Food and Drug Administration. FDA approves expanded use of Gardasil 9 to include individuals 27 through 45 years old [press release]. Published October 5, 2018. Accessed August 10, 2020.
- Saslow D, Andrews KS, Manassaram‐Baptiste D, et al. Human papillomavirus vaccination 2020 guideline update: American Cancer Society guideline adaptation. CA Cancer J Clin. 2016;66(5):375-85. doi:10.3322/caac.21355
- Walker TY, Elam-Evans LD, Yankey D, et al. National, regional, state, and selected local area vaccination coverage among adolescents aged 13–17 years — United States, 2018. MMWR Morb Mortal Wkly Rep. 2019;68(33):718-723. doi:10.15585/mmwr.mm6833a2