Date Published: June 27, 2017
Publisher: Public Library of Science
Author(s): Paul Bloem, Ikechukwu Ogbuanu
Abstract: In an essay, Paul Bloem and Ikechukwu Ogbuanu discuss the public health implications of HPV vaccination.
Partial Text: Human papillomavirus (HPV) is the most common sexually transmitted infection (STI) and can cause HPV-related cancers, most of which are cervical cancers, and genital warts. Although the majority of HPV infections are asymptomatic with spontaneous resolution, disease may result from persistent infection with high-risk HPV genotypes. While infection with a high-risk oncogenic HPV type is the underlying cause of virtually all cases of cervical cancer, most infections with high-risk HPV types do not lead to cancer. This is because infection persists only in a small percentage of people; only a small proportion of these persistent infections progress to precancer, and, of these, even fewer lead to invasive cancer .
For the first time in the history of STI prevention and control programmes, an intervention is available to prevent one of the most common STIs, HPV infection. Vaccines to prevent infection by high-risk oncogenic HPV types (16 and 18) and HPV types that cause anogenital warts (6 and 11) have been in use since 2006. HPV vaccines are most effective when administered before the onset of sexual activity. By preventing HPV infection, they could greatly reduce the morbidity and mortality from cervical cancers . Early-impact studies from high-income settings with high vaccination coverage have shown a reduction of up to 30% in cervical intraepithelial neoplasia grade 2+ (CIN2+) in 15 to 19 year old girls . Where the quadrivalent vaccine was used, data are showing a remarkable impact on the incidence of genital warts, including among unvaccinated males through herd protection .
Given 10 years of availability and the documented effectiveness of HPV vaccines, there remain wide global disparities in access to this intervention. Globally, by the end of 2016, nearly 70 countries (or 35% of all countries) have introduced the vaccine into their national immunisation schedule, either nationally or in a part of the country [9,10]. Unfortunately, full-dose vaccine coverage remains low in many settings. It has been estimated that between 2006 and the end of 2014, only 1.4% of the global population of women 10 to 20 years of age had received the full course of HPV vaccine .
The magnitude of the burden of cervical cancer coupled with the importance of anogenital warts and their impact on quality of (sexual) life, as well as the availability of effective and safe vaccines for prevention, have recently led to considerable policy attention in support of the introduction of HPV vaccines. In the context of the Decade of Vaccines, the Global Vaccine Action Plan promotes the introduction of new vaccines, including HPV vaccine . In 2012, the Gavi Alliance opened a window of support for HPV vaccine introduction, with an original target to reach 30 million girls in the least developed countries by 2020 . In addition, more recently, the UN Global Action Plan for the Prevention and Control of Noncommunicable Diseases identified cervical cancer as a priority preventable cancer and HPV vaccination as a key intervention . In 2016, the interagency task team on cancer set up a Joint UN Global Programme for the Prevention of Cervical Cancer to accelerate implementation of comprehensive cervical cancer prevention programmes, including vaccination in high-burden countries. Also in 2016, the World Health Assembly adopted the Global Health Sector Strategies on STIs, which endorse the effectiveness of HPV vaccination as a cost-effective STI prevention strategy and encourage countries to introduce the vaccine and achieve high coverage .
In addition to vaccine cost, a major barrier to HPV vaccine uptake is the lack of experience delivering a 2-dose vaccine to 9- to 14-year-old girls through routine immunisation programmes. Country experiences have shown that high coverage can be achieved in multiple settings. Several countries in different income categories have reported vaccination coverage levels above 80% (e.g., England and Mexico) or 90% (e.g., Malaysia and Rwanda). On the other hand, there are also examples of countries in which full-dose coverage remains below 50% more than 5 years following introduction (e.g., France and the US) .
In the 10 years since its introduction, HPV vaccination has seen many positive developments. A reduced number of doses and more flexible schedules have reduced costs and facilitated programme implementation. Recent clinical trials are assessing the efficacy and duration of protection offered by 1 dose of HPV vaccine, based on recent promising data on efficacy [24, 25]. The HPV vaccine market is also likely to evolve further. The 9-valent vaccine is expected to expand to markets beyond the US. Additional vaccine manufacturers are expected to introduce new and cheaper HPV vaccines. These positive developments are likely to significantly change the global HPV vaccine market in the coming years.