Data just released by the Australian Government show that many girls are not completing the full course of the cervical cancer vaccine. It’s another very good reason towards an already compelling case for vaccinating boys as well as girls against the human papillomavirus (HPV).
Women under 26 years, who are in a free catch-up program, and 12-year-old schoolgirls are supposed to be vaccinated against HPV.
The program has been largely successful but the latest data show many girls are not showing up for their second and third doses.
Arguments against vaccinating males overlook the range of protections afforded by the vaccines to homosexual men. Regardless of this, without full uptake by girls, coverage of heterosexual men can no longer be assumed either.
Human papillomavirus (HPV) is a group of over 100 closely related viruses, divided into “low risk” and “high risk” according to their tendency to cause cancer.
The cervical cancer vaccine currently in use in Australia’s National Immunization program – Gardasil – protects against four of these types, namely HPV 6, 11, 16 and 18.
HPV 6 and 11 are low-risk types from the point of view of cancer, but they cause more than 90% of cases of genital warts.
HPV 16 and 18 are high-risk types, and together cause about 70% of cervical cancer cases. Another HPV vaccine – Cervarix - is approved for use in Australia and protects against HPV 16 and 18 only.
Both vaccines prevent more than 90% of infections due to relevant HPV types.
Clinical trials have also tested the efficacy of HPV vaccines in preventing anogenital warts and precancerous lesions of the anogenital region and found they provide protection.
More recent research has indicated that the vaccines are very highly effective in preventing vulval, vaginal, penile and anal pre-cancer.
It is also generally believed that the vaccine will prevent HPV-associated cancers of the oropharynx. But as there is no known pre-cancerous lesion of the throat as a precursor to this cancer, randomized trials to definitively prove this are not possible.
Benefits of HPV vaccinations for males
Estimates suggest about one quarter of HPV–associated cancers in Australia currently occur in men.
In fact, of all HPV-associated cancers, only two are increasing in incidence - anal cancer and oropharyngeal cancers.
As these are cancers commonly affect men, in the future it is likely that HPV–associated cancers will increasingly do so.
HPV vaccines were initially developed and marketed as a form of cervical cancer prevention because it is the most common HPV-associated cancer in Australia.
Young heterosexual men in Australia will receive some protection against HPV, because most of their sexual partners - young women – will be vaccinated against HPV.
Some modelling studies suggest that there is only a relatively modest extra protection to be offered men by vaccination.
But they ignore additional ways in which young men might become infected, such as through sex with both local unvaccinated women and those born overseas.
Given the scale of the backpacker industry in Australia, and of overseas travel by young Australian males, this is not a trivial consideration. Critically, these studies also ignore the issue of transmission of HPV among homosexual men.
Undoubtedly in Australia, the population group most at risk of HPV-related disease is gay men. About 8% of men have a lifetime history of homosexual experience or attraction and about 2% identify as gay.
Rates of anal cancer are at least 20 times higher in gay men than in other men. Anal cancer is much more common in gay men than cervical cancer is in women.
Gay men will receive little if any protection against HPV if only women are vaccinated.
One potential solution is a program targeting homosexual men. However, such a program is very unlikely to be successful, as most homosexual men become HPV infected early in their sexual life, before they have gained the confidence and openness required to disclose their sexuality to their doctors.
And a targeted vaccination program did not work for another sexually transmitted infection – hepatitis B virus – in Australia. It has now been replaced by universal infant vaccination.
A targeted vaccination program is even less likely to be effective for HPV.
How would it be done?
Australia’s current national HPV immunization program targets all girls in their first year of secondary school. Pragmatically, all that’s required to include boys is to invite them to form an orderly line with the girls.
This would clearly require additional staffing for the process of vaccination, and critically, government funding for the vaccine.
If 80% of boys were also vaccinated, the risk of unvaccinated women developing HPV-related disease would be greatly reduced through so-called “herd immunity”, because four out of five of their heterosexual partners would be vaccinated.
While it is absolutely clear that the vaccine is effective in preventing HPV-related disease in boys, it is true that the amount of disease prevented in boys is somewhat less than in girls.
This means that to reach equivalent cost-effectiveness to that in girls, the vaccine would need to be made available more cheaply for boys. The argument is one of cost, not of effectiveness.
The addition of boys to our national immunization program for HPV would immediately double the pharmaceutical market, and economies of scale should be expected to bring down the cost of providing the vaccine.
Australia’s process of approval of drug pricing through the Pharmaceutical Benefits Advisory Committee should enable the fixing of a price representing value for money to the Australian taxpayer.