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Home » HPV immunization herd effect — it’s reducing infection in unvaxxed

HPV immunization herd effect — it’s reducing infection in unvaxxed

Immunization against HPV (human papillomavirus) has had a positive effect not only on vaccinated individuals but also on unvaccinated females according to a new peer-reviewed study. And the unvaxxed can be thankful that more and more young men and women are getting their HPV immunization.

I am a large proponent of the cancer-preventing HPV vaccine because it prevents several different cancers. Unfortunately, this same study showed that the HPV immunization rate is still quite low compared to other vaccines.

Let’s take a look at HPV, the HPV vaccine, and this new research.

Your HPV primer

I know I cut and paste this section to 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 they ought to know just how the HPV vaccine prevents cancer. 

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, just skip down to the next section where I discuss the key point of this article.

Genital and oral human papillomavirus (HPV) infections are the most common sexually transmitted infections (STI) 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:

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 the CDC, roughly 79 million Americans are infected with HPV – approximately 14 million Americans contract a new HPV every year. Most individuals don’t even know they have the infection until the onset of cancer. The CDC also states that over 46,000 HPV-related cancers are diagnosed in the USA every year. It may be 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.

Currently, in the United States, the Advisory Committee on Immunization Practices (ACIP) recommends that preteen girls and boys aged 11 or 12 are vaccinated against HPV. The immunization 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 teenage boys and young men up to the age of 21.

Let me sum this all up so that if you come away from this section with nothing else, you get this summary. HPV is a sexually transmitted disease. HPV causes 46,000 cancers a year in the USA alone. The HPV vaccine prevents becoming infected by HPV, which means you are protected from these cancers.

HPV immunization paper

In an article published in the Annals of Internal Medicine on 17 May 2022, researchers led by Hannah Rosenblum, MD, an epidemiology fellow with the CDC in Atlanta, and colleagues surveyed sexually active girls and young women, 14- to 24-year-olds, using data from the National Health and Nutrition Examination Survey.

Their key results were:

  • HPV immunization resulted in a 90% reduction in four types of cervical HPV infections in the studied group.
  • For unvaccinated females in the study, there was a 74% reduction of those four HPV types possibly because the unvaxxed females benefited from “strong herd effects or indirect protection. In other words, the HPV vaccine has led to a broad drop in HPV infections in both vaccinated and unvaccinated females.
  • They found no significant differences in the prevalence of non-vaccine-type HPV infections. These results suggest that other types of HPV infections did not replace vaccine-type HPV infections and that the decrease in vaccine-type infections was due to vaccination and not other variables.
  • Female and male vaccination rates increased to 59% and 29.5%, respectively, in 2015-2018. I think that there is a belief among a lot of people that the vaccine is more helpful for females rather than males. This is an incorrect belief.
  • Vaccine effectiveness in females appeared to drop from 84% in the 2011-2014 era to 60% in 2015-2018. Vaccine effectiveness last stood at about 51% in the 2013-2016 period for males. This may be concerning, but the authors wrote, “as herd protection increases and prevalence among unvaccinated persons decreases, vaccine effectiveness might be difficult to estimate. We do not believe that these findings raise concerns about waning immunity; multiple studies show long-lasting protection after HPV vaccination.”

These results are consistent with other studies (here and here) which have shown the near eradication of cervical cancer diagnoses before the age of 30 among women who received on-time HPV immunization.

According to Rebecca Perkins, MD, MSc, an OB/GYN at Boston University School of Medicine and Boston Medical Center, and colleagues who wrote in an accompanying editorial in the Annals of Internal Medicine,

These data are consistent with other sources, which also suggest substantial reductions in vaccine-type HPV infections and precancers among vaccinated populations.

Recent data also indicate near elimination of cervical cancer diagnosed before age 30 years among women who received on-time vaccination.

However, Perkins and colleagues added a somber note:

During the pandemic, providers and health systems have deprioritized adolescent vaccination, and particularly HPV vaccination, which in turn has led to more severe drops for HPV vaccination than for other adolescent vaccinations, and for adolescent vaccination compared with early childhood and adult vaccinations. Even as adolescents return for well visits and routine vaccinations, the need to compensate for the cumulative deficit of missed vaccinations over the past 2 years has created a serious and urgent threat to cancer prevention efforts, with a shortfall from which it may take a decade to recover.”

For their analysis, Rosenblum and colleagues used data from the National Health and Nutrition Examination Survey.

There were some limitations of the study, including the data the in survey were self- or parent-reported vaccination history and there were low numbers of participants from certain races or ethnicities.


Michael Simpson

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