A new HPV vaccine clinical study shows that one shot works as well as two. This means that we only need to give one shot of the cancer-prevention vaccine, saving money while knowing it’s just as effective.

The HPV vaccine hater, HHS Secretary Robert F Kennedy Jr, probably will scupper any changes to the HPV vaccine recommendations based on this study. I remain concerned that he will do anything he can to discredit the vaccine, and he may even pull it from the market.

This post will examine the results of the HPV vaccine clinical study and discuss what it may mean for vaccination recommendations.

HPV and the HPV vaccines

I know I cut and paste this section into every article I write about HPV vaccines, but it’s the first step to HPV vaccine myth debunking. Some readers may be coming here for the first time and should know how the HPV vaccine lowers cancer risks. 

However, I try to update this section when necessary with new information about either the disease or the vaccine. If you’ve read this section 47 times, skip to the next section where I discuss the key points of this article.

Genital and oral human papillomavirus (HPV) infections are the most common sexually transmitted infections (STIs) in the USA.  HPV is generally transmitted from personal contact during vaginal, anal, or oral sex.

It’s important to note that there are more than 150 strains or subtypes of HPV that can infect humans; however, only 40 of these strains are linked to one or more different cancers. Of those 40 strains, most are fairly rare.

Although the early symptoms of HPV infections aren’t serious and many HPV infections resolve themselves without long-term harm, HPV infections are causally linked to many types of cancers in men and women. According to current medical research, here are some of the cancers that are linked to HPV:

• Cervical cancer
• Vulvar cancer
• Vaginal cancer
• Anal cancer
• Oropharyngeal cancer (throat cancer)
• Penile cancer

In addition, there is some evidence that HPV infections are causally linked to skin and prostate cancers. The link to skin cancer is still preliminary, but there is much stronger evidence that HPV is linked to many prostate cancers.

HPV is believed to cause nearly 5% of all new cancers across the world, making it almost as dangerous as tobacco in that respect. According to published research, roughly 42 million persons in the USA are infected with disease-associated HPV, and 13 million persons acquire a new infection each year.

Each year in the United States, about 47,984 new cases of cancer are found in parts of the body where human papillomavirus (HPV) is often found — 26,280 among females, and 21,704 among males. 

Most individuals don’t even know they have the infection until the onset of cancer. The CDC states that over 37,800 HPV-related cancers are diagnosed in the USA every year. It is probably several times that amount worldwide.

There were two HPV vaccines on the world market before 2014. GSK, also known as GlaxoSmithKline, produced Cervarix, a bivalent (protects against two HPV strains) vaccine. It has been withdrawn from the US market (although available in many other markets) because of the competition from the quadrivalent (immunizes against four different HPV strains) and 9-valent (against nine HPV strains) Gardasil vaccines.

Merck manufactures Gardasil, probably the most popular HPV vaccine in the world. The first version of the vaccine, quadrivalent Gardasil, targets the two HPV genotypes known to cause about 70% of cervical cancer and two other HPV genotypes that cause genital warts. In Europe and other markets, Gardasil is known as Silgard.

The newer Gardasil 9, approved by the FDA in 2014, is a 9-valent vaccine that protects against HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58. It targets the four HPV strains found in the quadrivalent version, along with five additional ones that are linked to cervical and other HPV-related cancers. Both versions of Gardasil are prophylactic, meant to be given to females or males before they become exposed to possible HPV infection through intimate contact.

Gardasil is one of the easiest and best ways to prevent a few dangerous and, to abuse the definition slightly, common cancers that afflict men and women. Without a doubt, the HPV vaccine prevents cancer.

In the United States, the Advisory Committee on Immunization Practices (ACIP) currently recommends that preteen girls and boys aged 11 or 12 receive the HPV vaccine. The HPV vaccine is also recommended for teenage girls and young women up to the age of 26 who did not receive it when they were younger, and boys and young men up to the age of 21.

Let me sum this up so you get this summary if you leave this section with nothing else. HPV is a sexually transmitted disease. HPV causes 37,800 cancers a year in the USA alone. The HPV vaccine prevents one from becoming infected by HPV, which means you are protected from these cancers.

HPV vaccine one-dose study

The ESCUDDO Trial was launched in 2017 and included 20,330 girls, ages 12 to 16, randomized to receive either of the two HPV vaccines, Cervarix and Gardasil 9. In turn, those groups were randomized again to receive either one or two doses of the respective vaccines. All participants were followed every 6 months for 5 years with self-collected cervical samples.

Aimée Kreimer, PhD, National Cancer Institute, presented data at the American Association for Cancer Research annual meeting in Chicago. The researchers found that one dose of both the bivalent Cervarix and 9-valent Gardasil 9 HPV vaccines provided similar protection to two doses, with vaccine efficacy that exceeded 97%.

Dr. Kreimer presented the data in advance of the June 2025 meeting of the CDC’s Advisory Committee on Immunization Practices (ACIP). The committee may vote on a one-dose schedule during that June meeting. ACIP previously discussed this issue at its April 2025 meeting.

Other studies seem to support the one-dose vaccination schedule:

• A 2004 trial, sponsored by the National Cancer Institute, found that even one dose of the HPV vaccine was just as effective as two or three doses.
• A 2009 trial showed that one dose of the HPV vaccine was as effective as two or three doses.
• A 2011 non-randomized trial in Costa Rica found that one dose of the HPV 16/18 vaccine was as effective as three doses of the vaccine.
• The 2022 KEN SHE randomized trial in Kenya found that one dose of Gardasil 9 or Cervarix was 98% effective in preventing HPV 16/18 infection up to 3 years post-vaccination.

Summary

The evidence clearly shows that one dose of either Cervarix or Gardasil 9 is as effective as additional doses, with 97-98% vaccine effectiveness. If ACIP accepts these results and changes the recommendations for the HPV vaccine to a single dose, it can significantly reduce the cost of vaccination while maintaining equivalent effectiveness.

This means that the cancer-preventing HPV vaccine is highly effective and extremely safe. Even with one dose.

I am ebullient.

Citations

• Barnabas RV, Brown ER, Onono MA, Bukusi EA, Njoroge B, Winer RL, Galloway DA, Pinder LF, Donnell D, Wakhungu I, Congo O, Biwott C, Kimanthi S, Oluoch L, Heller KB, Leingang H, Morrison S, Rechkina E, Cherne S, Schaafsma TT, McClelland RS, Celum C, Baeten JM, Mugo N. Efficacy of single-dose HPV vaccination among young African women. NEJM Evid. 2022 Jun;1(5):EVIDoa2100056. doi: 10.1056/EVIDoa2100056. Epub 2022 Apr 11. PMID: 35693874; PMCID: PMC9172784.
• Kreimer AR, Rodriguez AC, Hildesheim A, Herrero R, Porras C, Schiffman M, González P, Solomon D, Jiménez S, Schiller JT, Lowy DR, Quint W, Sherman ME, Schussler J, Wacholder S; CVT Vaccine Group. Proof-of-principle evaluation of the efficacy of fewer than three doses of a bivalent HPV16/18 vaccine. J Natl Cancer Inst. 2011 Oct 5;103(19):1444-51. doi: 10.1093/jnci/djr319. Epub 2011 Sep 9. PMID: 21908768; PMCID: PMC3186781.
• Paavonen J, Naud P, Salmerón J, Wheeler CM, Chow SN, Apter D, Kitchener H, Castellsague X, Teixeira JC, Skinner SR, Hedrick J, Jaisamrarn U, Limson G, Garland S, Szarewski A, Romanowski B, Aoki FY, Schwarz TF, Poppe WA, Bosch FX, Jenkins D, Hardt K, Zahaf T, Descamps D, Struyf F, Lehtinen M, Dubin G; HPV PATRICIA Study Group. Efficacy of human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine against cervical infection and precancer caused by oncogenic HPV types (PATRICIA): final analysis of a double-blind, randomised study in young women. Lancet. 2009 Jul 25;374(9686):301-14. doi: 10.1016/S0140-6736(09)61248-4. Epub 2009 Jul 6. Erratum in: Lancet. 2010 Sep 25;376(9746):1054. PMID: 19586656.

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