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3 doses of HPV vaccine offers best protection against genital warts, study finds

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An illustration picture shows a Gardasil anti-cervical cancer vaccine box displayed at a pharmacy in Strasbourg. (REUTERS/Vincent Kessler)

As the human papillomavirus (HPV) vaccine becomes more widely used throughout the world, some researchers are asking whether the vaccine – administered in three doses over six months – could be as effective in just two doses.

HPV is a common virus, typically spread through skin-to-skin contact during sexual activity. Before a vaccine for HPV was introduced, most people unknowingly acquired the virus at some point during the course of their lives, according to the Centers for Disease Control and Prevention (CDC). Though HPV can be symptom-free, some strains of the virus can cause cancers, including cervical cancer and genital warts.  

In a study published in the Journal of the American Medical Association, researchers sought to examine whether women who received only two doses of the standard three-dose vaccine were more likely to contract genital warts.

“[Genital warts] are really the first outcome we can study,” study author Lisen Arnheim Dahlström, of the department of medical epidemiology and biostatistics at the Karolinska Institutet in Sweden, told FoxNews.com. “This question is quite interesting, especially now, since there is a debate or discussion [about] if two doses should be recommended instead of the three recommended today.”

While cervical cancer can take up to 15 to 20 years to develop, genital warts tend to occur within three to six months after a person is infected with HPV – making it an easy outcome for the researchers to analyze.

For their study, Arnheim Dahlström and her colleagues utilized Swedish health care registers to gather data on all women between the ages of 10 and 24 who received the HPV vaccine in Sweden from 2006 to 2010 – a cohort of more than a million people. The researchers divided the subjects into four categories: those who had not been vaccinated and those who had received either one, two or three doses of the vaccine. More than 80 percent of women studied received the full three doses of the vaccine.

Overall, the researchers identified 20,000 cases of genital warts amongst their subjects during the follow-up period, which lasted an average of 3.8 years. Women who received two doses had just a 71 percent protection rate against genital warts, while women who received three doses of the vaccine had an 82 percent protection rate. Furthermore, women who received three doses of the vaccine had a 43 percent better protection rate compared to women who received only one dose.

While the study indicates that two doses of the vaccine still offer some protection against warts, Arnheim Dahlström cautioned that more research needs to be done.

“I would say that the take home message from this study is that you should stick to the recommendations that are issued by your authorities, not to figure out your own schedule but to stick to the schedule that’s recommended until new recommendations are issued,” Arnheim Dahlström said.

However, she hopes future research and clinical trials will offer more insight into the effectiveness of the vaccine – noting that a two-dose vaccine could be cheaper and easier to administer.

“It would be cheaper for the developing countries that don’t have as much money as the rich countries do, but also…considering the infrastructure these countries have, it would be easier to administrate two doses instead of three,” Arnheim Dahlström said. “[And] I guess the discussion is also that in some countries, the compliance would be better with two [doses] instead of three.”