Skip to content
Home » Another study supports the Gardasil long-term safety

Another study supports the Gardasil long-term safety

I’ve written more than almost 200 articles about the safety and effectiveness of various versions of the HPV vaccine. As a result, I have focused a lot of those 200 articles on Gardasil long-term safety.

There have been huge studies, one that includes over 200,000 patients and another that includes over 1 million patients, that have provided solid and nearly incontrovertible evidence that support the Gardasil long-term safety – nevertheless, the anti-vaccine tropes and memes about the HPV cancer-preventing vaccine persist.

Though it is frustrating that some researchers publish “evidence” from small studies that are poorly designed in an attempt to invent issues with HPV vaccines if you look at the best designed unbiased studies, the facts are clear–Gardasil is safe and effective. It could be one of the safest and most effective vaccines since it was developed and studied in the era of harsh, and mostly unfounded, criticisms of vaccines by certain antivaccine activists.

All about HPV and Gardasil

Many of you have read this section an enormous number of times, however, for some of the readers of this blog, this article might be their first bit of research into the human papillomavirus (HPV) vaccine. Thus, it’s important to get a brief overview of HPV and the vaccines. If you’ve read this section before, just skip to the next section if you want.

Genital and oral  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. 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:

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 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. Accordingly, about 27,000 HPV-related cancers are diagnosed in the USA every year.

There were two HPV vaccines on the world market before 2014. GSK, also known as GlaxoSmithKline manufactured Cervarix, a bivalent 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 subtypes) and 9-valent (against nine subtypes) 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. It targets the four HPV genotypes 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 before females or males become exposed to possible HPV infection through intimate contact.

Gardasil is one of the easiest and best ways to prevent a few deadly cancers that are related to HPV. It is definitely a cancer-preventing vaccine.

(Just a quick note. There are actually two cancer-preventing vaccines. Along with the HPV vaccines, 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.)

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.

Another Gardasil long-term safety study

Despite the vast mountain of evidence supporting the Gardasil long-term safety, it doesn’t hurt to have one more. A new systematic review, published in the Pediatric Infectious Disease Journal, presented one of the largest reviews of clinical trials on the quadrivalent HPV vaccine (Gardasil). It found no evidence of any significant short- or long-term adverse events.

The authors combined data from clinical trials, post-licensing studies, and other data presented at scientific meetings (but, as of this date, not published). The researchers examined adverse events such as autoimmune diseases, neurological disorders, cardiovascular issues, and anaphylaxis.

Let’s make this simple – the researchers found that none of these serious adverse events were related to the HPV vaccine.

According to one of the co-authors of the study, Dr. Stanley Block, a pediatrician in Kentucky,

This is an incredibly well studied vaccine, with huge data sets and huge populations, and nothing has panned out as being significant as far as major adverse events,. We know the reality is that it protects against a tremendous number of deaths, cancers and chemotherapies for your daughters and your sons somewhat too.

The researchers examined over eight years of data from all types of clinical and epidemiological studies which represented over 2 million doses of the HPV vaccine given to young men and women.

The researchers specifically focused on two active safety surveillance studies in the USA and Denmark. Active studies involve actual examination of medical records of patients who have received the HPV vaccine. This is the best, and most scientific, method to find a correlation between a vaccine and a specific adverse event. According to the paper, these two active safety surveillance studies included over 1.6 million doses of the vaccine, and they found that “serious adverse events (AE) were extensively studied and showed no increase in the incidence of these AEs compared with background rates.”

Passive surveillance data

Many people point to the passive data derived from the Vaccine Adverse Event Reporting System (VAERS) to condemn the safety of HPV vaccines. VAERS is considered “passive” because it does not separate temporal events (that is, an event that happens coincidentally after a vaccination) from causal events. VAERS is a system where individuals can report supposed (and sometimes actual) adverse events post-vaccination, to “prove” certain adverse events are related to the vaccination.

The authors stated that first two years of VAERS data following the HPV quadrivalent “vaccine licensure found disproportional reporting venous thromboembolism (VTE).” VTE, which is a condition where a blood clot breaks loose and travels in the blood, can be serious. However, the possible association of HPV vaccine with VTE was evaluated in the active surveillance studies, mentioned above, and no association was found between vaccination and VTE. And there is no valid biological plausibility that there could be a relationship between Gardasil and VTE.

VAERS is one of the favorite “research tools” of the anti-vaccine religion, although, if used properly, VAERS can provide “observational data” that could indicate to an epidemiologist a need to establish a hypothesis and determine if controlled data supports or rejects the hypothesis that a vaccine is correlated or causally linked.

For example, as recently explained to me by science writer Tara Haelle, observations from VAERS and other passive sources led to the observation that intussusception is associated with rotavirus vaccinations. Although the risk of intussusception is small (especially compared to the various risks of the rotavirus infection itself), parents are asked to be aware of symptoms in case of the rare event. In this case, observational data were used appropriately.

But the problem is that VAERS reports can be made online, by fax or by mail, without medical records that assist in finding potential causal relationships. Passive data needs to be compiled and reviewed before we spend the time to seek out potential causality. Most of the VAERS data probably is not very helpful in understanding risks of the HPV vaccine, especially long-term.

Most epidemiologists know it is probably valueless. Even the VAERS system itself says that the data cannot be used to ascertain the difference between coincidence and true causality. For example, there are tropes across the internet that claim that some number of girls have died from the HPV vaccine, using VAERS data as a “source.” Irrespective of causality, there is, sadly, a background rate of mortality, across all causes, irrespective of whether an individual is vaccinated or not. Unless we understand the background rate of mortality, the vaccine “mortality” rate has no scientific meaning.

VAERS sometimes is used as a feel-good system for those who think that there’s a link between vaccines and something terrible, but without an active investigation, most of the data is not very useful, and it takes a lot of work to find data that might help form a hypothesis about Gardasil safety.

What does this all mean, TL;DR

  • Huge active surveillance studies have shown that are no causal links between HPV vaccines and serious adverse events.
  • Those same studies rejected the hypotheses, formed by VAERS data, that HPV vaccines were related to venous thromboembolism.

HPV vaccines save lives by preventing cancer. HPV vaccines are safe. Not sure what else I can write.


This article was first published in July 2015. It has been updated, copyedited, and reformatted to keep it fresh and up-to-date. In addition, with the continued anti-vaccine attacks on HPV vaccines for ridiculous reasons, it’s important to remind the audience that large epidemiological studies show it is demonstrably safe.

Key citations:


Michael Simpson

Don’t miss each new article!

We don’t spam! Read our privacy policy for more info.

Liked it? Take a second to support Michael Simpson on Patreon!
Become a patron at Patreon!