Texas Governor Rick Perry has taken a lot of flak for mandating that adolescent girls in the Lone Star State should be vaccinated against the human pappilomavirus (HPV). But Perry’s policy might have a strong scientific grounding. According to a report published today in PLoS Medicine, blanket vaccinating young girls might be the most effective way of curbing the cancer-causing virus.
A team led by Johannes Bogaards, a biostatistician at the VU University Medical Centre in the Netherlands, devised a mathematical model of sexually transmitted infections to investigate whether vaccinating males only, females only or both sexes was the best way to reduce the prevalence of such diseases. The researchers found that single-sex vaccination was most effective, and that the sex vaccinated should be the one with the highest prevalence of the disease.
Since HPV is more common among girls than boys, “vaccinating additional females is more effective in blocking transmission and reducing the population prevalence of infection than it is to start vaccinating males,” Bogaards says.
That conclusion runs counter to recent policy recommendations made by the US Centers for Disease Control and Prevention (CDC). In October, the agency recommended that young boys should be vaccinated alongside their female schoolmates to help stem the transmission of the virus.
Despite the Dutch team’s analysis, however, Joseph Bocchini, chairman of the CDC advisory committee on HPV, stands by his agency’s recommendations. He notes that sociopolitical stigma and misinformation have led to low vaccination rates in the US that upset many of the assumptions of the Dutch model. As such, he explains, “the fewer women who are immunized the more we stand to gain from vaccinating boys.”
The mathematical model also assumes only heterosexual disease transmission, notes pediatrician Luis Barroso of Wake Forest University in North Carolina. The analysis “doesn’t take into account men having sex with men,” who would get “no protection at all from vaccinating women,” he says. That’s why, in addition to adolescent boys, the CDC’s October report recommended vaccination for men up to age 26 if they have sex with other men.
Such disagreements within the scientific community reflect the difficulty of creating an epidemiological model that can be widely applied. One thing epidemiologists, biostaticians and policymakers all agree on is that the HPV vaccine is safe, effective and should be widely implemented. Convincing parents of that fact is proving to be the most difficult obstacle to overcome.