Dr Melina Georgousakis explains why a vaccine originally given to girls to help prevent cervical cancer also has a lot to offer boys.
Starting in 2013, human papillomavirus (HPV) vaccination will be offered to boys through schools. While of course boys can't get cervical cancer, HPV can cause cancers in males. To better understand how HPV vaccination will benefit boys, it is important to know what HPV is and how the vaccine works.
What is HPV, and who gets it?
HPV is a common sexually transmitted virus. It is estimated that before HPV vaccination, four out of five people would get an HPV infection in their lifetime. Most HPV infections don't cause symptoms, and will eventually disappear on their own. However, in a very small number of people infected with HPV, the virus will stay around for many months and sometimes years. These long-lasting infections have the potential to result in cancer, as the virus has a chance to interact with the body's cells, changing how they behave and turning them into cancer cells. Although cervical cancer is the most well-known disease caused by HPV, long-lasting HPV infections can potentially lead to other cancers such as those of the head and neck, and non-cancerous diseases such as genital warts that can affect males and females.
How does the HPV vaccine work?
By preventing HPV infection in the first place, vaccination prevents any diseases the virus might have caused. There are more than 100 different types of HPV, but only some of them can cause cancer. The two HPV types responsible for most (at least 70 per cent) cervical cancers, as well as most other HPV-associated cancers, are HPV types 16 and 18. Both HPV vaccines available in Australia prevent infection from these types. The HPV vaccine Gardasil also prevents infection from HPV types 6 and 11, which are the most common cause of genital warts. It is important that women continue to get pap smears even if they are vaccinated against HPV.
Why is HPV vaccination given to teenagers?
There has been some confusion about why HPV vaccine is given to teenagers when cancers caused by HPV don't usually appear until adulthood. HPV vaccines protect against these cancers by preventing the initial HPV infection, which occurs through sexual contact. As the vaccine is only effective if it is given before contracting an HPV infection, it is important to vaccinate before sexual activity starts. Generally, the older a person, the more likely they would have already experienced an HPV infection via intimate contact, and the less likely the HPV vaccine will work. For this reason the HPV vaccination program has provided Gardasil to girls 12 to 13 years of age through schools. In 2013, schools will also offer the vaccine to boys aged 12 to 13 years. Boys up to 15 years of age will also be able to receive Gardasil in schools via a catch-up program over the next two years.
Why is the vaccine being offered to boys?
Cervical cancer is the most common HPV-associated cancer worldwide, so the majority of HPV research has been focused on understanding the role of HPV in causing that type of cancer. HPV-vaccine development was initially focused on preventing cervical cancer, therefore the first clinical trials involved only girls and women. However, as research has continued, much more is now known about the role of HPV in causing cancers in males (such as penile, anal, head and neck cancers) and how the vaccine can help prevent them.
Is the vaccine worthwhile for boys?
A major clinical trial of Gardasil involving boys and men showed the vaccine was as effective at preventing genital HPV infection and early pre-cancer changes in males as it was at preventing cervical HPV infection and pre-cancer changes in females. It also showed the vaccine was as safe for males as it was for females. Not only will HPV vaccination help prevent HPV infection for individual males, but research suggests vaccinating boys will contribute to increasing protection against HPV in girls due to 'herd immunity' (when the majority of people in a population have been vaccinated, thereby protecting unvaccinated people in the same environment).
Has the vaccine been successful?
In the five years since HPV vaccination for females was introduced in Australia, we have seen reductions in genital warts and cervical pre-cancerous changes. For example, a study of new cases of genital warts diagnosed in a sexual-health clinic in Melbourne before and after the introduction of HPV vaccination found that in women under 21 years of age (who would have been eligible to receive the free HPV vaccine) genital warts declined from 18.6 per cent to 1.9 per cent. If vaccine uptake in adolescent boys is as high as it is in adolescent girls (nearly 80 per cent), then Australia will no doubt see even greater benefits from this vaccine in the future.
Dr Melina Georgousakis is senior research officer at the National Centre for Immunisation Research and Surveillance, Sydney.