An irrational fear of increased sexual promiscuity is an unexpected foe in the fight against cervical cancer and genital warts.

Indeed, the percentage of the population vaccinated against the human papillomavirus is far below what scientists deem “socially optimal” — in large part because of the perception that HPV vaccination increases promiscuity, a recent Yale School of Public Health study found. The findings also suggest that HPV vaccine costs must be lowered substantially to encourage adequate vaccination.

“Public perceptions regarding adolescent promiscuity had the most significant impact on … vaccination levels among the topics we analyzed,” the researchers wrote in the paper, which was published in December.

Existing medical research, however, does not validate such a fear and the finding starkly contradicts the fundamental assumption that students learn in Economics 101: individuals are wholly rational.

“I think that there is absolutely no evidence to support that ,” Yale University Health Services director Paul Genecin said. He added that no studies to date have shown that providing various forms of intervention — such as birth control, condoms or the HPV vaccine ­— actually increases sexual activity.

One potential implication of the study is that an initiative to educate the public on the real benefits and risks of the preventative measure could substantively increase vaccinations among the critical populations, said Allison Galvani, an assistant professor in the department’s Division of Epidemiology of Microbial Diseases.

“A fundamental but often-neglected aspect of developing and implementing an optimal intervention program is human psychology, which influences adherence to recommendations,” she said.


Despite the fact that both men and women can contract and transmit HPV, the study showed it is most efficient for the female population to be vaccinated.

Specifically, it is socially optimal for 67 percent of females and 0 percent of males to receive the vaccine. When 67 percent of females were vaccinated, the study found that the marginal benefit of male vaccination was negligible. (The optimal level of vaccination was defined as that which maximized health-related benefits and minimized health and health-related costs for the aggregate population.)

At present, however, less than 25 percent of the target population has received at least one of the vaccines in the three-part HPV series.

In order to determine the optimal level of vaccination, researchers developed and used an epidemiological game-theory model of HPV vaccination and examined how public-perception driven vaccination levels compared with the socially optimal vaccination level.

In addition to being a multifaceted study, public health professor A. David Paltiel said the researchers’ use of mathematical modeling, game theory and psychology to analyze such a complex issue was a “brilliant model of interdisciplinary collaboration.”

“I think the paper is a model of the kind of collaboration we should be encouraging more and more,” he said. “It is an example of the kinds of work we need to be doing on these thorny issues.”


The study found that, in addition to a public relations campaign on the benefits and risks of the vaccine, it is necessary to lower the cost of each dose by $55 to increase adequately individuals’ willingness to vaccinate.

On-campus, demand for the HPV vaccine has been steady, Genecin said.

“I know that there has been a swift demand and I know that a number of women have sought the vaccine,” Genecin said.

At present, students who have Yale health insurance coverage beyond the basic Yale Health Plan pay for the vaccine as they would most other prescriptions — a $100 deductible and 20 percent of the remaining cost. Fees for other students depend on their particular insurance plan.

The only vaccines covered under the basic plan are the flu shot and post-exposure vaccines that would be necessary to stop the spread of an infection in a classroom or dormitory setting.

On average, a family pays $181 out of pocket for a child to receive all three vaccinations.