Human papillomavirus: women carry the greater cancer burden related to HPV but men are also affected.
The authors of the study do, however, say that the first priority in delivering cancer benefit for both sexes is to ensure the highest possible uptake of the human papillomavirus (HPV) vaccination by girls, which counters the viral infection linked, for them, to cervical cancer.
But further to the knock-on benefit for men brought by reducing HPV circulation among females in this way, there can be added direct effects of vaccinating boys, they say.
The study finds that, after higher vaccine coverage among girls, the additional benefit against the HPV-related cancers that affect men - anal, penile and some throat cancers - would come from preventing the infection among men who have sex with other men.
Johannes Bogaards and Johannes Berkhof at VU University Medical Centre in Amsterdam, with colleagues, designed their study to estimate the cancer benefits to men if boys were vaccinated in their country as well as girls.
In the Netherlands, universal coverage is only for girls; aside from the US, the few places to have a policy for the injection of boys too include Australia, Austria and two provinces in Canada.
Using the Dutch national cancer registry and epidemiological studies, the authors analyzed the impact of HPV vaccination on cancers affecting men linked to the papillomavirus. Their conclusion is:
"Men will benefit indirectly from vaccination of girls but remain at risk of cancers associated with HPV.
The incremental benefit of vaccinating boys when vaccine uptake among girls is high is driven by the prevention of anal carcinomas, which underscores the relevance of HPV prevention efforts for men who have sex with men."
An editorial commenting on the study - written by Karen Canfell, DPhil, director of Cancer Council NSW, a cancer research organization in Australia - supports the priority for vaccination of girls, but which in turn reduces the need to vaccinate all boys and therefore also the cost-to-benefit ratio of doing so.
Dr. Canfell, also an associate professor at the Prince of Wales Clinical School of the University of New South Wales, says the findings "reinforce those of prior analyses that found that adding boys to established vaccination programs in girls becomes less cost-effective as female coverage increases."
This is a point also made by the study authors - that universal vaccination of boys comes with serious cost-to-benefit considerations for populations.
Inclusion of boys into preadolescent HPV vaccination programs is warranted, they say, "once the incremental costs of vaccination conform to society's willingness to pay in comparison with the incremental health effects."
Potential male cancer benefit of vaccinating all boys is comparatively small
Uptake of the injection in girls may be considered more important for male cancer reduction than US-style programs to vaccinate all boys.
The study estimated a combined measure of the quality and quantity of life gained by cancer prevention, by looking at the quality-adjusted life years (QALYs) for men before and after HPV vaccination introduction in The Netherlands.
Before the program came into effect, they estimate that about 15 such life-years attributable to HPV-related cancers were lost for every 1,000 men.
The authors give a reduction in this cancer burden of over one third - 37% - if vaccine uptake in the country remains at the current level of 60% coverage.
But if this uptake among girls were to rise to 90%, the study suggests that the male burden of HPV-related cancer would be cut by two thirds - by 66%.
The potential results of introducing coverage for boys in each scenario of female injection are that, in the 90% uptake picture, more than 1,700 boys would need to be vaccinated to prevent one additional male cancer case.
With the current 60% picture of Dutch female coverage, 800 boys being injected would bring that same single cancer case reduction.
These potential benefits for males are substantially less favorable, say the authors, than those that motivated the universal vaccination of girls to protect women against cervical cancer. Four times fewer girls than boys need to be injected to prevent one cancer case:
"In the Netherlands, the number of girls that needed to be vaccinated to gain one QALY from cervical disease prevention was about 25, and around 200 to prevent one case of cervical cancer."
Therefore, the authors say, the efficiency of vaccinating "boys aged 12 against oncogenic HPV needs ultimate assessment in a health-economic evaluation."
Australia is the only country so far to have an HPV immunization campaign for men that is publicly funded.
Health priorities differ where women's protection still needs to improve
Dr. Canfell argues that although it is appropriate for richer countries to follow the US in considering vaccination of boys, the current cervical cancer prevention priorities in low- and middle-income countries should remain focused on females.
She says the development of programs that integrate vaccinating young girls with screening older women are the way forward, adding: "Based on experience in developed countries, this will also provide benefits for men through indirect vaccine protection."
The case for this approach is based on the fact cited by Dr. Canfell that 87% of the 610,000 worldwide cancers annually attributable to HPV are in women - cancers of the cervix - and three quarters of these occur in countries with a low or medium human development index.
Cancer: protection against sexually transmitted infection is only part of the challenge when cervical cancer rates will rise as a component of aging.
In developed countries meanwhile, such broader efforts to prevent cervical cancer in women are less of a concern, where the focus "has now, appropriately," shifted to considering the following issues for "boys, men who have sex with men, and older women:"
- Burden of HPV-related disease
- Safety, effectiveness, acceptability, equity and cost-effectiveness of vaccination.
For women's burden of HPV-related disease, the editorial points out that vaccination is increasingly only part of the concern, and outside of the richest countries, hundreds of millions of older women would remain at risk "even if" a substantial majority of young girls were vaccinated.
This is because vaccination alone will not prevent the effect of population aging "driving" increasing cervical cancer numbers over the next few decades.