Two doses of the human papillomavirus (HPV) vaccine are enough to protect children, younger than 15, from genital warts. The study — which looked at nearly 400,000 girls in the U.S. — provide the first real-world evidence that supports national and global recommendations that two doses of the vaccine are enough in this age group.
Last year, the Centers for Disease Control and Prevention (CDC) issued the two-dose recommendation for those younger than 15 after reviewing data from clinical trials. The data showed that the immune response was similar after two and three doses. The World Health Organization (WHO), likewise, recommended two doses, based on this information.
But up to now, no studies had shown that this really translated to a protection from virus infection.
The study, “Impact of Number of Human Papillomavirus Vaccine Doses on Genital Warts Diagnoses Among a National Cohort of U.S. Adolescents” — published in the journal Sexually Transmitted Diseases — did just that.
“The CDC and WHO based the new two-dose schedule primarily on immunogenicity results, but there was very little research on how effective that recommendation has been,” Rebecca Perkins, MD, an obstetrician at Boston University Medical Center and the study’s lead author, said in a press release.
“This study validates the new recommendations and allows us to confidently move forward with the 2 dose schedule for the prevention of genital warts,” she added.
Perkins and her research team compared rates of genital warts in girls who had received one, two, three, or no doses of the vaccine.
Those receiving either two or three doses had a similarly good protection from genital warts, compared to girls who received only one dose, or who were not vaccinated.
Statistics show that the introduction of the vaccine has been effective in preventing genital warts, but its aim is not merely to reduce these rates. Since the virus is the main driver of cervical cancer, it is crucial to study how the dosing regime impacts long-term outcomes of HPV infection, such as cervical dysplasia and cancer, researchers said.
“The data supporting a two-dose schedule is encouraging, but it only reports on genital warts, not cervical dysplasia or cancer outcomes. Collecting that long term data is paramount,” said Perkins, who is also an associate professor of obstetrics and gynecology at Boston University School of Medicine.
“This study will be a stepping stone for future research into the effectiveness of the two-dose schedule of the HPV vaccine for other symptoms of the disease.”