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Mathematical Model Says HPV Vaccine Should Only be Given to One Sex but Experts Disagree

Martha Kempner

A new study using a mathematical model suggests that public health efforts should focus on vaccinating either boys or girls against HPV but not both. The findings seem to counter a recent decision by the CDC which recommends vaccinating boys as well, but experts here say it is not time to start cancelling our son’s pediatrician appointments.

The HPV vaccine is back in the news today.  This fall it was the subject of political debate as Republican presidential candidates jumped on one-time-front-runner Rick Perry for having mandated the vaccine in his home state of Texas and his one-time-top-rival Michele Bachmann swore it caused mental retardation.  That controversy eventually died down (and some suggest brought Ms. Bachmann down with it) but then the CDC recommended that the vaccine, which prevents the strains of HIV most likely to cause cervical cancer, be given to boys as well as girls (it had previously been approved for both but only routinely recommended for girls ages 9 to 26). This week, a new study is out which questions the public health merits of this vaccination approach but experts are saying we should stay on course nonetheless. 

The study, published this week in the journal PLoS Medicine, was conducted by researchers in Vienna and uses a mathematical model of STD spread between heterosexual individuals to determine the best approach to vaccination. The research concluded that the most effective way to reduce HPV infection was to vaccinate either boys or girls because in the case of heterosexual transmission of the virus, vaccinating one sex will protect the other.  The lead researcher explains:  “If you have a limited amount of vaccine, vaccinating 100 percent of women and 0 percent of men will lead to a greater reduction in HPV infections than vaccinating 50 percent of women and 50 percent of men.”  He goes on to argue that since most countries have already begun to vaccinate girls (and they are the sex with the highest prevalence), we should continue to focus on that and only once most girls are vaccinated should we move on to vaccinating boys.

The findings seem to counter the recent decision by the CDC about vaccinating boys, but experts here say it is not time to start cancelling our son’s pediatrician appointments.  First, they point out that it is just one study.  In addition, this model is based on the idea that a country could get all or nearly all girls vaccinated yet the CDC recommendations were made, at least in part, because the percentage of girls being vaccinated in this United States was low. 

Dr. Joseph Bocchini, professor and chairman of pediatrics at Louisiana State University also notes that there are flaws in all mathematical modeling.  “All models make assumptions, which may not necessarily hold up in the real world,” Bocchini said.

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This model is notably focused on heterosexual transmission of HPV.  The researchers did conduct a separate analysis which “assumed a small percentage of the population was men who have sex with men,” and say it did not change the overall results though they acknowledged that under a model that targets only women for vaccination, “men who have sex with men were not maximally protected.”    

This is one of the reasons that Dr. Paul Offit, of the Vaccine Education Center at the Children’s Hospital of Philadelphia, cited when he suggested we stick to the policy that targets both sexes.  Offit argues that only a policy that includes men can reach men who have sex with men and possibly help prevent anal cancer, which can also be caused by HPV, among this group. He also pointed to the early efforts to vaccinate against hepatitis B, the only other STD for which there is a vaccine.  The vaccine was originally recommended only for high risk groups but that made very little difference in the incidence of the disease. As Offit explained, “In 1991, the policy changed to vaccinating all infants, and the disease is now virtually eliminated in young people.” 

So despite this new research, it is likely that the CDC recommendations will stick and maybe, if politicians stay out of it and parents start listening to public health experts, we can virtually eliminate HPV as well. 

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