Gardasil 9 at 10 Years: A Brief History

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 proven 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,” said Paula M. Cuccaro, PhD, an assistant professor of health promotion and behavioral sciences at University of Texas School of Public Health, Houston, 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. 

Increasing Uptake

The current public health aim is to have 80% of young people in the targeted age group vaccinated with two doses. Today, uptake among those 9-26 years old stands at about 78% of girls and 75% of boys for the first dose, said Annunziata. “But it’s only about 61% for the two doses in the current series, and we want to improve that.” 

Some parents may still harbor fears that immunizing teens and tweens — both the American Academy of Pediatrics and the American Cancer Society recommend immunization at age 9 — will open the door to precocious sexual activity. 

“But overall, uptake in tweens and young teens has increased because the messaging has changed,” said Myers, with the rationale now focusing on cancer prevention not sexual-infection prophylaxis. “This is similar to the hepatitis B vaccine, which used to be given to young adults and is now given to newborns to prevent cancer.” 

Cuccaro added that a proactive presentation by healthcare professionals has a significant effect on vaccine uptake and increases the odds of vaccination ninefold. “Providers should take a presumptive approach and avoid just offering the vaccine as an option. It should be included with regular childhood vaccinations,” she said. “And the advantage of starting early at age 9 is that you can spread the doses out across other regular childhood vaccinations, whereas if you start at age 11, you need to add the HPV vaccine to three other vaccines that are given at that time.” 

After age 15, three doses are necessary. “Providers should stress to parents that it’s most effective when given before young people become sexually active and exposed to HPV,” Cuccaro said. And Myers stressed that despite the vaccine’s effectiveness, routine screening for cervical premalignancies is still important. 

Despite increasing coverage, vaccination rates have some distance to go before the public health target of at least 80% uptake of the series in the targeted age group, Cuccaro cautioned.

On the global stage, barriers to immunization remain, but the World Health Organization has endorsed a campaign to eradicate cervical cancer through HPV vaccination. It has predicted that the 21st century may be the last to experience HPV-associated cancers, currently responsible for more than 300,000 annual deaths worldwide.

A Brief History of HPV Vaccines

• 1951. Cervical cancer patient Henrietta Lacks’ rapidly dividing cervical cells are collected by George Gey at Johns Hopkins Hospital. They create the first immortal cell line (HeLa) used to study cancers and vaccines worldwide.
• 1976. Harald zur Hausen suggests that genital wart-associated HPV, not herpes simplex, is the probable cause of cervical cancer.
• 1983. HPV is confirmed as a cause of cancer.
• 1991. The first HPV vaccine is developed.
• 2002. Proof of principle and protective efficacy for the monovalent HPV 16 are shown.
• 2006. Merck’s Gardasil 4 (HPV 4) is FDA approved in girls ages 9-26 for protection against strains 6, 11, 16, and 18 — the cause of more than 70% of cervical cancer cases.
• 2009. Approval of Gardasil 4 is expanded to boys ages 9-26 for the prevention of genital warts.
• 2009. The FDA approves GlaxoSmithKline’s Cervarix (HPV 16 and 18) for girls and young women. The vaccine was withdrawn from the US market in 2016 following the success of Gardasil 9 but is used abroad for HPV cancer prevention.
• 2014. The 9-valent recombinant vaccine Gardasil 9 is FDA approved for protection against several low-risk, wart-causing HPV strains as well as the high-risk cancer strains targeted by HPV 4.
• 2018. The FDA expands approval to include females and males 27-45 years old.
• 2020. The FDA extends approval of Gardasil 9 to include prevention not only of cervical cancer but also, vaginal, vulvar, anal, oropharyngeal, and other head and neck cancers.

Annunziata, Cuccaro, and Myers had no competing interests to declare.

Diana Swift is a medical journalist based in Toronto, Canada