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  • Alex Cloherty

What does HPV do, and who gets the vaccine?

HPV, or human papillomavirus, is the most commonly sexually transmitted infection, but many people aren't very aware of this pesky microbe. Scientists estimate that the risk of being infected at least once during your life, regardless of gender, is about 50%, which is a good reason to understand more about both the infection and the vaccine.

One of the reasons why the risk of infection with HPV is so high, is that there are many different types of HPV and not all of them cause a long-lasting infection. In fact, the human immune system is so good at what it does that most HPV infections are cleared out by the immune system alone, with no symptoms. Many people who have had an HPV infection will be totally unaware of it – and therefore will be unaware that they are infecting people around them with the virus. This wide variation in HPV symptoms is possible is because there are many different types of HPV, just like how there are many different types of flu virus. In fact, over 200 different types of HPV have been described by scientists, based on small differences in the DNA of the viruses. These multitudes of different viruses types can cause a variety different, but related, problems, which are all based on the same root cause: growths.

More specifically, the most common symptoms of HPV are either benign growths (warts) or malignant growths (cancer). HPV types 6, 11, 16, and 18 are the ones that cause the most problems – 6 and 11 are common causes of genital warts, while 16 and 18 are responsible for several different types of cancers. These more nasty HPV types have evolved to possess slightly different DNA, and therefore proteins, than their less dangerous sibling HPV types.

All HPV viruses are able to make, among other proteins, a pair of proteins called "E6" and "E7" (I know, scientists don't always think up very interesting names). These two dully dubbed proteins are considered to be the most important HPV machines for making the virus cause harm to humans. In high-risk HPV types, E6 and E7 together are able to "immortalize" their human target cells. This might sound good at first - we usually think of being immortal in a pretty positive light. However, immortalization of cells is most definitely a bad thing for us humans. It's actually a good thing that our cells eventually die, and make space for new, healthy cells to replace them. When human cells are immortalized, they stick around past their time, and build up... And up... And up. This build-up of excess cells is what we commonly call a tumour.

From a scientific point of view, the main difference between the warts (benign tumours) and cancers (malignant tumours) caused by HPV is that the immortalized cells in warts don't spread to other parts of the body. Warts are only irritating in the one small part of the body that is infected with the virus, while the immortalized cells in cancers can spread and cause problems elsewhere.

HPV is associated with warts and cancers in both men and women, but luckily, there are vaccines that can protect against at least some of the nastier HPV strains! The most basic HPV vaccine protects only against types 16 and 18, which cause cancers, but additional vaccines have also been developed to protect against more of the harmful HPV types. If you're familiar with the HPV vaccine, though, you may be thinking, "If HPV can cause warts and cancer in both men and women, why are only women vaccinated?"

Indeed, in some countries, such as the Netherlands, only females receive the HPV vaccine routinely, despite two of the common HPV vaccines (Gardasil and Gardasil-9) being approved for use by males. This is purely for economic reasons. HPV is only life threatening for males when it causes penile or anal cancers, but these are much less common than cervical cancer. Therefore, it's much less cost-effective to vaccinate men than women. It's also more cost-effective to vaccinate people before they become sexually active, so that the chance of them already being infected with HPV is low. It is these economic considerations that result in only pre-adolescent females being vaccinated in many countries.

In my opinion, though, it's better to be safe than sorry. If you have the means to be vaccinated against HPV, regardless of your age or gender, I think it makes a lot of sense to do so. The most common side-effects of the HPV vaccine are things like headaches and nausea, which I'd much rather get than cancer. Let me know if you disagree and why!

Until next week - vaccinate wisely (i.e. just vaccinate)!

- Alex

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