Although I have no poll numbers sitting in front of me, and certainly no scientific peer-reviewed research, I just have a feeling that if you scratch the surface of an anti-vaccine activist, you will find that if they could hate one vaccine, it would be Gardasil. And one of the arguments will be all about Gardasil effectiveness – they claim it doesn’t actually prevent cancer.
When you couple their false claims about the dangers of the vaccine with the claims about the lack of Gardasil effectiveness, you’d probably agree with the anti-vaccine crowd. Despite these false claims, HPV vaccine uptake has slowly grown in the US and other countries.
I’ve written nearly 200 articles about the HPV cancer-preventing vaccine, but most of those are focused on debunking myths and confirming the safety of the vaccine. I’m going to focus on a quick primer about Gardasil effectiveness in preventing cancer. Stay tuned for some interesting science.
All about HPV vaccines
You’ve probably read the following few paragraphs enough times to quote them without looking. Actually, I add information as necessary to make sure you have up-to-date facts and figures about the HPV vaccine.
However, for some of you, this might be your first bit of research into the human papillomavirus (HPV) vaccine, so it’s important to get a brief overview of HPV and the vaccines. If you’ve read this before, just skip to the next section if you want.
Genital and oral HPV are the most common sexually transmitted infections (STI) in the USA. There are more than 150 strains or subtypes of HPV that can infect humans, although only 40 of these strains are linked to a variety of cancers. HPV is generally transmitted from personal contact during vaginal, anal or oral sex.
Although the early symptoms of HPV infections aren’t serious, those infections are closely 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:
These are all dangerous and disfiguring cancers that can be mostly prevented by the HPV cancer vaccine. If you’re a male, and you think that these are mostly female cancers, penile cancer can lead to amputation of your penis. Just think about that guys.
HPV is believed to cause nearly 5% of all new cancers across the world, making it almost as dangerous as tobacco with respect to cancer. 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. About 27,000 HPV-related cancers are diagnosed in the USA every year.
There were two HPV vaccines on the market before 2014. GSK, also known as GlaxoSmithKline manufactured Cervarix, a bivalent vaccine, but it has been withdrawn from the US market, because of the competition from the other HPV vaccines. In Europe and other markets, Gardasil is known as Silgard.
Merck manufactures the other HPV vaccines. Its first vaccine, the quadrivalent Gardasil, targets the two HPV genotypes known to cause about 70% of cervical cancer and two other HPV genotypes that cause genital warts. The newer Gardasil 9, approved by the FDA in 2014, is a 9-valent vaccine. It targets the four HPV genotypes in the quadrivalent version, along with five additional ones that are linked to cervical and other types of cancer. Both versions of Gardasil are prophylactic, meant to be given before females or males become exposed to possible HPV infection through intimate contact.
There are precious few ways to actually prevent cancer – it does not include drinking your favorite whey protein-blueberry-kale-quinoa-seaweed smoothie every day. Quit smoking. Stay out of the sun. Maintain a healthy weight. Quit drinking. And get your HPV vaccine.
(Just a quick note. There are actually two cancer-preventing vaccines. Along with Gardasil, the hepatitis B vaccine is also important for the prevention of some cancers. The vaccine prevents hepatitis B viral infections. Chronic hepatitis B infections can lead to liver cirrhosis or cancer. Liver cancer is actually one of the few cancers in the USA where the incidence has increased over the past few years. And if you follow the anti-vaccine rhetoric, you know the hepatitis B vaccine is almost as controversial as the HPV vaccine.)
HPV and cancer
Research published in Cancer and the Journal of the National Cancer Institute reviewed cancer statistics and pathology which formed the basis of the chart above. You can quickly see the number of HPV-related cancers by cancer and by subtype of HPV in the USA every year. According to this research, there are about 31,500 new cancers every year that are linked to HPV.
Of those new HPV-related cancers, 29,100 are caused by HPV subtypes that are blocked by the relatively new Gardasil9 vaccine. I know, many of you are going to look at that 29,100 and think, “well, that’s not that many people.”
I think one of the myths about cancer is that it’s a raging epidemic and half the world is afflicted by one cancer or another. But most cancers are quite rare, and most have unknown etiologies. However, we know that the seven cancers listed in the chart above are mostly caused by HPV. These HPV-related cancers, if grouped together, would be ranked in the top 20 list of cancers across the world.
Sure, the most common cancers, like lung, breast, prostate, and colon, are substantially more common than HPV-related cancers. But, other than lung cancer and smoking, these other cancers cannot be prevented by anything known today – certainly not as easy as getting an HPV vaccine.
Cervical cancer and HPV
Gardasil was initially developed to prevent cervical cancer, but, as we have seen, it is useful for preventing at least six other cancers too. But I thought I would focus on cervical cancer since it shows us the evidence that HPV actually causes cancer.
As I wrote above, HPV is linked to numerous cancers (including some not listed such as, potentially, skin cancer). How do we know this? Because we’ve studied the pathology of several cancers, including cervical, and have found that the human papillomavirus has transformed the cell in ways that make it cancerous.
A systematic review (considered the pinnacle of the hierarchy of scientific research) of cervical cancer concluded that “most SCNC and LCNC (small-cell and large-cell neuroendocrine cancers of the cervix) are caused by HPV, primarily HPV18 and HPV16. Therefore, most if not all SCNC and LCNC will be prevented by currently available prophylactic HPV vaccines.”
Another study states that “Cervical cancer is initiated by high-risk types of the human papillomavirus (hrHPV) and develops via precursor stages, called cervical intraepithelial neoplasia (CIN).”
The science supporting a causal link between HPV infections and various types of cervical cancer is clear. The scientific consensus supports this link, and dismissing it out of hand is not supported by the evidence.
Not all cervical cancers are caused by HPV (although, as we saw in the chart above, about 90% are). Not all HPV infections in women cause cervical cancer, most HPV infections resolve themselves.
As we see in the chart in the previous section, the number of new HPV-related cervical cancers cases each year in the USA is relatively small – about 10,600. But 4,115 women died in 2014 from this cancer.
Given the powerful evidence that HPV is linked to cervical cancer, and it kills about a third of the women who contract it, it seems logical that preventing the HPV infection in the first place is a good thing. The argument from the anti-vaccine world is that it’s “only” 4,000 deaths and only 11,000 new cases. I don’t understand why the anti-vaccine world dismisses 4,000 deaths as if it is not relevant.
The other issue is that the time period from infection to diagnoses of cancer can be decades. Many people cannot imagine that some infection that they get in their 20s has something to do with cancer 30 years later. But it may not actually be that infection – remember some of the HPV subtypes are so common, each of us might get re-infected several times in our life, especially if we have more than one or two sexual partners. In addition, the course of many cancers takes a significant amount of time.
Most cancers are relatively rare, but there’s no known way to prevent most of them. And here we have a very safe (despite the claims of the anti-vaccine world) vaccine that will prevent one deadly cancer.
Gardasil effectiveness against HPV infections
Unless someone has a serious amount of evidence against the link between several HPV subtypes and those seven cancers, we can move on. We know that HPV is causal to at least seven cancer – now, we need to determine if the HPV vaccines are effective at preventing HPV vaccines. And the evidence to support Gardasil effectiveness is robust and overwhelming.
A large systematic review (and let me remind the reader once again, systematic reviews are the gold standard of biomedical research) of Gardasil effectiveness studies found that the HPV vaccines are highly effective in preventing the transmission and spread of many HPV subtypes:
Although HPV models differ in structure, data used for calibration, and settings, our population-level predictions were generally concordant and suggest that strong herd effects are expected from vaccinating girls only, even with coverage as low as 20%. Elimination of HPV 16, 18, 6, and 11 is possible if 80% coverage in girls and boys is reached and if high vaccine efficacy is maintained over time.
Of course, I’m troubled by a herd effect from only 20% coverage (and in the USA, HPV vaccine uptake is around 60%) – but the researcher’s analysis seems solid. But if we can get 80% coverage, we might eliminate the four most common HPV subtypes. That would be amazing, allowing a generation of teens and young adults to not worry about the cancers that afflict humans today.
In another study I analyzed, the researchers observed that the oral HPV infection rates in the vaccinated group were about 88% lower than those individuals who were not vaccinated. Moreover, the investigators actually found no infections in vaccinated males, which would suggest that Gardasil may reduce the prevalence of those infections by as high as 100%. HPV-related head and neck cancers disproportionately affect males, so this data may be important in increasing Gardasil vaccination rates in males.
Another study, published in Pediatrics (and reviewed by me), by Dr. Lauri Markowitz and her colleagues, provided strong evidence that the HPV vaccination schedule is directly linked to a reduction in HPV infections.
Dr. Markowitz investigated the rates of HPV infection among teens in the USA after the introduction of the HPV vaccine. She found that the infection rate, in teens aged 14 to 19, dropped by 64% in the six years after the vaccine was added to the recommended vaccination schedule. Furthermore, the infection rate dropped by34% among people ages 20 to 24.
In case you’re asking, there is simply no evidence that the decline was caused by a sudden nationwide teen celibacy increase. Of course, there is just no link between sexuality and the HPV vaccine, so there’s that.
One of the “criticisms” of Gardasil effectiveness is that we don’t know how long the vaccine will work. So there’s another study, published in Pediatrics, provides evidence that the effectiveness, measured by the immunity provided by the HPV vaccine, lasted at least 8 years. The study followed 1781 children, ages 9-15, for 8 years following vaccination with the HPV quadrivalent vaccine (about ⅔ of the group) or a placebo (about ⅓). At month 30, the placebo group received the vaccine.
The researchers determined the effectiveness of the vaccine by testing the participants’ blood for anti-HPV seropositivity (that is, an indication of antibodies to HPV in the blood). The results of the study provide more powerful evidence of the effectiveness of the vaccine. They concluded that vaccination-induced anti-HPV response was clinically detectable through month 96 (or 8 years).
Over time, we will get additional studies published that will check the long-term immune status of vaccinated individuals. Maybe in year 25, we notice a drop in immune status, and we could recommend a booster shot. That is how science works, it keeps gathering and analyzing data to revise original claims about the vaccine.
I could go on and on and on. There are over 800 published articles that discuss Gardasil effectiveness – almost all of them support the overall importance of the HPV vaccine in preventing cancers. (And yes, I’m sure some anti-vaccine activist will cherry pick some poorly designed article published in a predatory journal, and then claim that I’m wrong.)
The TL;DR summary of Gardasil effectiveness
First, we have robust and nearly irrefutable evidence that several subtypes of HPV are causally linked several deadly cancers. Second, we have similarly strong evidence that HPV vaccines either reduce HPV infections or reduce the actual risk of cancer.
To make specious claims that the HPV vaccine somehow doesn’t prevent cancer is typical vaccine denial – understate the benefits of vaccines and overstate the dangers (if there actually are any). It’s terribly frustrating because there are children that can be protected against cancer.
Gardasil is demonstrably effective, as you have read above. It is demonstrably safe. Protect yourself and your loved ones from cancer – you’ll thank me down the road.
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