"The gender with the lowest coverage is the low-hanging fruit," says Marc Ryser. "Stagnating vaccination rates, coupled with parental opposition, suggest that it could cost less to raise coverage in boys from, say, 14 to 15 percent than to raise coverage in girls from 37 to 38 percent."(Credit: Sam/Flickr)


Time to rethink ‘girls-only’ approach to HPV vaccine?

Encouraging parents to have their sons get the human papillomavirus (HPV) vaccine—rather than just trying to get more girls vaccinated—could ultimately protect more people for the same price, according to a study by a mathematician.

Whether vaccinating boys against HPV in addition to girls would only divert scarce resources from a campaign originally designed to help prevent cervical cancer has been a matter of debate.

But with HPV-related cancers in men on the rise, and HPV vaccine coverage for girls in the United States stagnating well below the critical levels needed to ensure that most people are protected, researchers have been re-examining the case for a girls-only approach.

Male HPV cancers on the rise

Although the virus is most frequently associated with cervical cancer, women aren’t the only ones at risk. The Centers for Disease Control estimates that a third of the 27,000 cases of cancer HPV causes in the US each year occur in men, where it can cause cancers of the throat, tongue, tonsils, penis, and anus.

More than half of all people in the US will get HPV at some point in their lives. Most infections go away on their own within one or two years. But some persist, and if left untreated can become cancer.

Studies suggest that HPV-related throat and mouth cancers are on the rise in the US, and could outnumber HPV-related cervical cancers by 2020.

Many of these cancers could be prevented with vaccination. But despite Centers for Disease Control recommendations that both boys and girls ages 11 to 12 should receive the HPV vaccine, only 37 percent of girls and 14 percent of boys in the US have received all three shots in the HPV vaccine series—much lower than the proportion needed to keep the disease in check.

Do the math

To find out whether different strategies for allocating public funds might protect more people, researchers developed a mathematical model of HPV transmission among sexually active 14-18 year olds.

They then compared the effectiveness of HPV vaccination campaigns based on different cost scenarios. One set of scenarios reflected the costs of vaccinating more people based on the per-dose price of the vaccine. Another set of scenarios also accounted for the patient education costs that could be required to reach people who are less willing to have their children vaccinated.

Over the past three years, HPV vaccination coverage in girls has stagnated. Studies suggest that 44 percent of US parents are reluctant to vaccinate their kids against a sexually transmitted infection before their child becomes sexually active—even though the vaccine works best if it is given before there is any chance of exposure, when there is still time to build up immunity.

Boosting coverage in girls to sufficient levels to protect everyone could become increasingly expensive, says Marc Ryser, a mathematician at Duke University,  especially as the pool of willing parents shrinks and only the more skeptical parents remain.

Parents of boys

“Imagine that 100 parents are offered HPV vaccines for their children,” says coauthor Evan Myers, professor of obstetrics and gynecology. “Some fraction will be willing to have their child vaccinated without any questions, some won’t have their child vaccinated under any circumstances, and the rest will be in between.”

“Along the spectrum of ‘Whatever you say, doctor’ to ‘I don’t believe in any vaccinations,’ families who are currently unvaccinated are closer to the resistant end of the spectrum, and so it takes more work and costs more money to try to persuade them,” Myers says.


Real-world data on actual patient education costs are needed before the results can be translated into policy, the authors say.

But their analysis suggests that public health officials may actually be able to protect more people for the same price by shifting some funds to encourage vaccination of boys, since the fraction of parents willing to vaccinate has yet to be exhausted among boys.

“The gender with the lowest coverage is the low-hanging fruit,” Ryser says. “Stagnating vaccination rates, coupled with parental opposition, suggest that it could cost less to raise coverage in boys from, say, 14 to 15 percent than to raise coverage in girls from 37 to 38 percent.”

“Making that trade-off would be beneficial to the entire population,” says coauthor and mathematician Kevin McGoff, since boosting coverage in either sex means fewer people can transmit the disease to uninfected people.

David Herzog of Drake University and David Sivakoff of Ohio State University were also authors of the study. The National Institutes of Health and the National Science Foundation funded the study.

Source: Duke University

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