Female-only HPV vaccination most effective
Increasing vaccination for the human papillomavirus (HPV) among pre-adolescent girls is more effective than extending existing programs to include boys, according to a range of transmission models.
Looking at heterosexual models, the researchers found that female vaccination was the most effective way to reduce HPV infection in the entire population. In most of the scenarios entered into the model, the preferred method was to vaccinate the group with the highest rate of infection in the time before the vaccine was available, reported Johannes A. Bogaards, from the VU University Medical Center in Amsterdam, and colleagues.
"Our results provide a justification, under most circumstances, for the intuitively plausible strategy of targeting intervention at the subgroups that harbor most infections and that act as a reservoir for transmission," they wrote.
More elaborate mathematical models, according to the research published online in PLoS Medicine, were also constructed, including one based on age and differing levels of sexual activity. This model confirmed that the preferred strategy should be a girl-only program.
The researchers used modeling tools to assess how vaccination can be best distributed in order to lower HPV prevalence. In addition to a model of heterosexual transmission, they also built one to include a population of men who have sex with men (MSM).
A major question in vaccination programs against sexually transmitted diseases is whether it is efficient and effective to direct the intervention at both genders, or only one.
The authors assumed 5% of the population is MSM, of whom 80% are bisexual. In this scenario, the strategy of vaccinating the sex with highest prevalence still resulted in the best population outcomes under the model -- over 90% in susceptible-infected-susceptible models of disease stage and over 80% in susceptible-infected-resistant models.
Related HPV reductions might still be beneficial to the MSM group, according to the researchers. They stressed that targeted vaccination of homosexual and bisexual men in the context of anal cancers is an important topic for future study.
As with all mathematical models, altering the variables results in different outcomes. The authors noted that differing degrees of natural immunity in the population as well as the extent of gender differences in transmission rates could derive new conclusions.
They believe further testing of targeted intervention at the subgroups showing the highest endemic prevalence is an optimal strategy. They noted that allocation of a fixed amount of vaccine that results in the greatest population reduction in prevalence may not be the most economically viable scheme.
"By exploring various two-sex transmission models, we demonstrate that directing prophylactic intervention at a single sex more effectively reduces heterosexual sexually transmitted disease transmission that any allocation that includes both sexes," the authors wrote. "In addition we demonstrate that a strategy of protecting the sex with the highest endemic prevalence generally achieves the largest reduction in population prevalence."
This research was supported by the Health Research and Development Council of the Netherlands Organization for Scientific Research.
Bogaards and one co-author received unrestricted research grants from GlaxoSmithKline (GSK). Bogaards has served as a consultant for Sanofi Pasteur MSD. Another co-author reported serving as a consultant for GSK and Sanofi Pasteur MSD. Other authors declared no competing interests.
By Kurt Ullman
Primary source: PLoS Medicine Source reference: Bogaards JA, et al "Sex-specific immunization for sexually transmitted infections such as human papillomavirus: Insights from mathematical models" PLoS Med 2011; DOI: 10.1371/journal.pmed.1001147.
Source: MedPage Today