The greatest reductions were seen in girls who were vaccinated when they were adolescents, with up to 73% reduction in cervical pre-cancerous lesions.
The use of Merck’s Gardasil led to reductions in the rates of high-grade (precancerous) and low-grade cervical lesions, according to a literature review recently published in the journal Expert Review of Vaccines. The vaccine also led to reductions in some non-cervical HPV-related diseases and HPV infection in women and men.
Human papillomavirus (HPV) is a common sexually transmitted infection, according to the CDC. In most cases, HPV goes away on its own within two years. But it can cause health problems like genital warts and cervical and other cancers, including cancer of the vulva, vagina, penis, or anus. It can also cause cancer in the back of the throat, tongue and tonsils.
“These real-world data from more than one hundred published studies show decreases in vaccine-type HPV infections and related diseases and are an important reminder that we need to do more to expand vaccination to males and females as part of the global fight to lessen the incidence of certain HPV-related diseases and cancers,” Ravinder Dhawan, vice president, head of center for observational and real-world evidence, Merck Research Laboratories, said in a press release.
Investigators, which included researchers from Merck, evaluated 138 peer-reviewed studies published between March 1, 2016, and March 31, 2020, to assess the impact and effectiveness of Gardasil through immunization programs in 23 countries, across Africa, Asia, Europe, Australia, South America and North America. MEDLINE, EMBASE, and Google Scholar were last searched on April 1st, 2020, for peer-reviewed observational studies on the HPV vaccines.
This research builds on a previous real-world analysis of 58 peer-reviewed studies published between Jan. 1, 2007, and Feb. 29, 2016, across Australia/New Zealand, Europe and North America. The updated analysis includes data from low-income countries such as Bhutan and Rwanda and lower-middle-income countries such as India and Mongolia. The World Health Organization has identified a global strategy to eliminate cervical cancer as a public health problem by 2030. This includes making sure 90% of girls are fully vaccinated with the HPV vaccine by age 15.
This analysis is important, investigators said, given that there is a vaccine hesitancy and a public distrust of vaccine. In lower income countries where the need is greatest, access to vaccines is limited.
In the recent analysis, the greatest reductions were seen in younger age groups (between 14 and 17 years of age), with up to 73% reduction in cervical pre-cancerous lesions among vaccinated girls. Sixteen studies reporting on non-cervical disease endpoints were also reviewed. Consistent decreases were seen in vaccine-type HPV infection rates in girls and women among age groups targeted by national immunization programs, of up to 96%. Additionally, a significant reduction in high-grade anal pre-cancers was seen among vaccinated versus unvaccinated men who have sex with men in one study.
“Three countries have demonstrated dramatic vaccine induced reductions in cervical cancer incidence,” the investigators wrote. “In countries with gender-neutral vaccination (GNV) programs, we expect to see more rapid declines in cervical cancer incidence and in time significant reductions in other HPV-related cancers occurring among men such as cancers of anus, penis, and head and neck.”
One limitation of this analysis was the heterogeneity of the studies included for review. Because of the variety of outcomes, diversity of populations, and countries with different programs, the results could only focus on general trends. The full impact of vaccination on HPV-related cancers is limited because of the long latency of these cancers and because there isn’t routine screening for oral and anal cancer. Studies from 2017 to 2018, however, showed early effects of HPV vaccination on cervical cancer, especially in the United States. Additionally, the impact of vaccination on men is limited and more data is needed.