One Shot, Two Shot, HPV Shots

HPV two dose vaccine in preteen girls appears similar to three doses in women

(RxWiki News) The only vaccine that can prevent a type of cancer is the HPV vaccine. But it requires three rounds of shots. Wouldn't it be nice to make it just two shots?

A recent study revealed that two shots in preteen girls was just as effective as three shots in young women at providing immunity against HPV.

However, when looking closer at the preteen age group, researchers found that two shots do not appear to offer the same protection as three shots in that age group.

"Talk to your child's pediatrician about vaccine schedules."

Human papillomavirus (HPV) is a sexually transmitted virus which can cause genital warts, cervical cancer in women, some head and neck cancers, and penile and anal cancers in men.

The study, led by Simon R. M. Dobson, MD, of the Department of Pediatrics at the University of British Columbia in Vancouver, Canada, aimed to see whether receiving just two HPV shots would provide the same protection as three shots.

The researchers began the study with 830 females, split into three groups. One group of 310 young women, aged 16 to 26, received three doses of the HPV vaccine.

The other group, preteen girls, aged 9 to 13, were randomly assigned to receive either three doses of the HPV vaccine or two doses of the vaccine.

A group 261 preteen girls who received three doses got their boosters at two and six months after the first shot. A group of 259 preteen girls who received two doses got the booster shot six months after the first shot.

The researchers were able to follow and collect blood samples for immunity with 675 of the original participants over the following three years.

The girls' immunity to HPV was measured in blood samples at the time they received the first dose and then 7 months, 18 months, 2 years and 3 years after that first dose.

When the researchers compared the young women with three doses to the preteen girls who received two doses, the two-dose immunity was found to be as effective as the three-dose regimen in women for HPV-16 and HPV-18.

HPV-16 and HPV-18 are two of the strains the HPV vaccine protects against which cause the majority of the cancers associated with HPV.

Overall, the immunity levels against all four of the HPV strains that the shot protects against were sufficient in the girls who got two doses when compared to the immunity of the women who got three doses through all the blood tests, up to three years later.

However, the researchers found slightly different results when they compared the two groups of preteen girls.

Seven months after getting the first shot, both the girls who got two shots and the girls who got three had similar enough immunity levels against all four HPV strains.

By the second year after the first shot, however, the girls who got only two doses had reduced immunity to HPV-18 when compared to the preteen girls who got three doses.

By the third year, the preteen girls who got two shots also had reduced immunity for HPV-16 when compared to the preteen girls who received three shots.

The researchers therefore concluded that more research is necessary before they can determine whether the dosage for the HPV vaccine can be reduced from three shots to just two shots.

The study was published April 30 in JAMA. The research was funded by the Ministries of Health in British Columbia, Nova Scotia and Quebec. Merck Laboratories Inc. paid for the antibodies analysis.

Nine of the authors reported various financial ties, including grant funding, honoraria, speakers' fees, travel fees and advisory board services, to about a half dozen pharmaceutical companies, including Merck and GlaxoSmithKline, which both manufacture an HPV vaccine.

Review Date: 
April 29, 2013