Vaccination against human papilloma virus (HPV), a group of more than 200 viruses infecting at least 50% of sexually active people over their lifetimes, has proved more than 90% effective for preventing several diseases caused by high-risk HPV types.
Gardasil 4: 2006
It started in 2006 with the approval of Human Papillomavirus Quadrivalent, types 6, 11, 16, and 18 (Gardasil 4). Merck’s vaccine began to lower rates of cervical cancer, a major global killer of women.
“It’s fair to say the vaccine has been an American and a global public health success story in reducing rates of cervical cancer,” Paula M. Cuccaro, PhD, assistant professor of health promotion and behavioral sciences at University of Texas School of Public Health, Houston, said in an interview.
How does a common virus trigger such a lethal gynecologic malignancy? “It knocks out two important cancer suppressor genes in cells,” explained Christina Annunziata,MD, PhD, a medical oncologist and senior vice president of extramural discovery science for the American Cancer Society. HPV oncoproteins are encoded by the E6 and E7 genes. As in other DNA tumor viruses, the E6 and E7 proteins functionally inactivate the tumor suppressor proteins p53 and pRB, respectively.
US Prevalence
Despite screening and vaccination, cervical cancer is still very much around. This year, 13,820 new cases of invasive cervical cancer will be diagnosed in the United States, and approximately 4360 women will die of it, according to the American Cancer Society. Even before the advent of Gardasil 4, incidence rates had already decreased by more than half from the mid-1970s to the mid-2000s, thanks largely to Pap smear screening programs for treatable premalignant lesions. “The US rate had dropped to about 20 per 100,000 women even before Gardasil 4,” said Annunziata. “After the introduction of the first vaccine, it decreased to 7 per 100,000, a decrease of about 30%, but it remains plateaued now at about the same level.”
Although the past decade has seen rates generally stabilize, there have been some changes in different age groups. In women ages 30-44, rates increased 1.7% each year from 2012 to 2019, while rates declined 11% each year for women ages 20-24— probably reflecting the impact of the first wave of prevention from Gardasil 4.
In one 2021 population-based study of US cancer registry data from 1999 to 2017, rates of both cervical squamous cell carcinoma and adenocarcinoma dropped. The largest declines occurred in females 15-20 years old, the age group most likely to be vaccinated against HPV but not typically screened, suggesting a vaccine-related effect.
Gardasil 9: 2014
With the 2014 approval of the vaccine’s second iteration, Gardasil 9, which replaced Gardasil 4 and targeted 9 HPV strains, immunization has taken broader aim. The strains covered by Gardasil 9 protect against oropharyngeal and other head and neck cancers — as well as penile, anal, vulvar, and vaginal malignancies and premalignancies, and genital warts in both sexes ages 9-45.
It may be years, however, before the impact of the newer polyvalent formulation is felt. “While the first vaccine has been successful against the prevalent strains of HPV linked to cervical cancer, it’s a little early to call it for the newer vaccine since oropharyngeal cancers tend to develop later in older men,” Cuccaro said. “But the types of HPV linked to mouth and throat cancers and covered by the newer vaccines are much less prevalent in those who are vaccinated. The strains not covered in the vaccine you see are equally present in the vaccinated and non-vaccinated.”
Angela L. Myers, MD, MPH, division director of infectious diseases and medical director of the Center for Wellbeing at Children’s Mercy in Kansas City, Missouri, added, “Unlike for cervical cancer, there are no screening programs for oropharyngeal lesions, so you have to wait to see rates until actual cancer develops.”
A 2023 review reported that HPV vaccination reduced levels of oropharyngeal HPV positivity in men, strengthening the case for pangender immunization.
And in a recent phase 3 doubled-blind trial, GARDASIL 9 reduced the incidence of anogenital persistent infection caused by nine types of HPV compared with a placebo.