By Anne Harding

NEW YORK (Reuters Health) - Giving girls younger than 15 two doses of the human papillomavirus (HPV) vaccine, at least six months apart, will probably provide adequate protection against cervical cancer while also being cost-effective, according to new findings published online January 7 in the BMJ.

"Our study shows that if this protection from two doses lasts at least 20 years, then the additional benefit of giving a third dose is likely to be very small," Mark Jit, of Public Health England in London, the first author of the new study, told Reuters Health. "On the basis of this evidence, the UK has adopted a two-dose vaccine schedule as it is likely to provide good protection and make sense economically."

However, he added, "Women 15 years old and above should continue to receive three doses of HPV vaccine as there is currently no evidence that two doses will give adequate protection in this age group."

In clinical trials, females who received three doses of either of the two available HPV vaccines (Gardasil and Cervarix) were protected from persistent HPV infection as well as precancerous lesions related to infection, Jit and his team note in their report. New findings suggest that a two-dose schedule in girls 9 to 14 years old could be as effective as a three-dose schedule in 15- to 25-year-olds. Based on these findings, the European Medicines Agency has allowed two-dose schedules to be marketed for girls younger than 15.

To investigate the cost-effectiveness of the two- and three-dose schedules with either vaccine, the researchers created a transmission dynamic model of HPV infection. They found that at a cost of 86.50 pounds per dose (about $131.50 U.S.) and assuming the vaccine protected 12-year-old girls for 10 years, Gardasil would be cost-effective, and adding a third dose at the same price would also be cost-effective if it resulted in lifetime protection.

Assuming that the two doses protected women for 20 years, the 86.50 per dose would still be cost-effective, but a third dose to provide lifetime protection would only be cost effective at a price of about 31 pounds. Results were similar for Cervarix at 80.50 per dose (about $122.35 U.S.).

"Based on the strong immune response that girls below 15 years get when they receive two vaccine doses (spaced at least six months apart), there is good reason to believe that protection will be long-lasting," Dr. Jit said. "However, countries giving these girls two-dose vaccine schedules will need to monitor HPV virus circulation to make sure that the protection is maintained.

"Protection (from either two or three doses of the vaccine) may last for decades," he added. "If it does, it will be a long time before we see vaccine protection wane and hence know how long protection lasts."

This research was supported by London School of Hygiene and Tropical Medicine in partnership with Public Health England. The authors reported no disclosures relevant to this study.

SOURCE: http://bmj.co/1tP6pjW

BMJ 2015.