Partial HPV Vaccine May Prevent Genital Warts in Girls

Genital human papillomavirus  (HPV) is the most commonly sexually transmitted infection in the United States. Close to 20 million Americans between the ages 15 and 49 are infected with the virus.

There are more than 40 types of HPV. Some types are considered low-risk and may cause genital warts, while others are high-risk and can cause several kinds of cancer, with cervical cancer being the most common. Many people who become infected do not even know they have it until symptoms or cancer appears. Anyone who has ever had sex (even with just one person) or will have sex in the future will most likely be exposed to the virus.

That's why it is extremely important that all young girls and boys, between the ages of 9 and 26, receive the recommended 3 doses of the HPV vaccine.

A new study from Sweden suggests that girls who receive only 2 of the 3 recommended doses may still be protected from genital warts. However, the study doesn't address the more serious issue of cervical cancer prevention – which is the primary reason for girls to get the HPV vaccine.

"This is the first study investigating the effectiveness of the HPV vaccine in the population by dose level," said lead researcher Lisen Arnheim-Dahlstrom, an associate professor in the department of medical epidemiology and biostatistics at the Karolinska Institute, in Stockholm.

"It is important to bear in mind that we have been studying genital warts, which is the first measurable disease outcome that we can study after vaccination because of its short incubation time. Cervical cancer takes a much longer time to develop than genital warts and is not as common," she said.

For the study Arnheim-Dahlstrom and colleagues collected data from national Swedish health registries on more than 1 million girls and women aged 10 to 24 who were followed between 2006 and 2010.

Of more than 20,000 cases of genital warts, only 322 happened after a female had received at least one dose of the vaccine, the researchers found.

Although the maximum reduction in risk was found after three doses, two doses also were protective, but to a lesser degree.

According to the researchers, the difference between three and two doses was that with two doses there would be 59 more cases of genital warts per 100,000 women who were observed for one year.

The vaccine is most effective when it is given to a girl before she's been exposed to HPV. The U.S. Centers for Disease Control and Prevention (CDC) recommends that boys and girls get the full three doses of the vaccine starting at age 11 and 12. 

The number of girls and boys who have received the vaccine has increased since it was approved in 2006, with 54 percent of girls getting at least one dose, but slightly less than 7 percent have received all three doses.

Even though the Swedish study suggests that 2 doses of the HPV vaccine may help prevent genital warts, experts recommend that girls receive all three doses to help prevent cancer, the more dangerous and possibly fatal disease.

Sources: Steven Reinberg,

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