Although the main purpose of the human papillomavirus vaccine is to protect girls from cervical cancer, genital warts caused by certain types of the virus is also prevented by the vaccine. Now, researchers have found that fewer doses of the vaccine still results in risk reduction of genital warts.
Outcomes of the latest study, which researchers say is the first to report a link between human papillomavirus (HPV) vaccination and genital warts by vaccine dose level, were recently published in JAMA.
The team notes that typical HPV vaccination requires three doses, but this latest study shows that two doses in girls younger than 17 was linked with a "considerable reduction in risk" of genital warts, also known as condyloma.
"Determining vaccine dose-level protection is essential to minimize program costs and increase mass vaccination program feasibility," write the authors.
So, to determine the association between number of doses and genital warts, the team, led by Eva Herweijer of the Karolinska Institutet in Stockholm, Sweden, assessed an open cohort of all females between the ages of 10-24 living in Sweden.
Using the Swedish nationwide population-based health data registers, the team looked at data on over 1 million girls who were followed up regarding HPV vaccination and first occurrence of condyloma between 2006 and 2010.
Study only accounts for genital warts, not cervical cancer risks
Girls who received only two of the three HPV vaccine doses were protected from genital warts in a similar way to those who received all three.
The team notes that, compared with vaccine efficacy trials, population-based studies like this one are able to analyze disease reduction and are more likely to reflect the actual vaccinated population.
In this cohort, there were a total of 20,383 new cases of genital warts. Of these, 322 occurred after receipt of at least one dose of the HPV vaccine.
Although the researchers found that the best risk reductions occurred after three doses, girls who received two doses were also protected. They add that there was a slight difference in cases prevented by three versus two doses.
The study authors explain:
"The number of condyloma cases prevented by three doses vs. two doses was 59 cases per 100,000 person-years, which is a small difference."
Although these findings are promising for the vaccine, the authors warn that their study only accounts for genital warts outcomes, not cervical cancer. They say more long-term studies need to be conducted to determine whether these results apply to cervical cancer.
A November 2013 study published in the journal Cancer Prevention Research suggested that one HPV vaccination could be enough for cervical cancer prevention, but the researchers from that study also cautioned that further research needs to be done.
Medical News Today recently compiled an in-depth story about the importance of regular screening for cervical cancer. Because of increased screening for the disease, the number of deaths caused by it have significantly decreased over the past 40 years.