HPV Vaccine Reducing Infections, Even Among Unvaccinated: Study
Findings suggest 'herd immunity' taking hold against leading cause of cervical cancer
By Jenifer Goodwin
HealthDay Reporter
MONDAY, July 9 (HealthDay News) -- Even among unvaccinated girls and young women, the human papillomavirus vaccine is reducing infections of certain strains of the virus known to cause genital warts and cervical cancer, new research finds.
The study is among the first to show signs that the human papillomavirus (HPV) vaccine not only prevents infections, but it can also promote herd protection -- a decrease in infections among the unimmunized thanks to lower rates of infections among other people in their community who might otherwise be transmitting the disease.
HPV is the most common sexually transmitted infection in the United States, and is thought to be the leading cause of cervical cancer. Certain strains of the virus can cause other health problems as well, including other genital cancers, anal cancer, head and neck cancers, and genital warts, experts say.
The study involved two groups of women aged 13 to 26 who had already had sexual contact and who were seen at two primary-care clinics in Cincinnati, one of which was a teen health center.
One group was seen at the clinic in 2006 or 2007, before the HPV vaccine, which protects against four strains of HPV, was widely available. The second group was seen in 2009 or 2010, after the vaccines were widely available.
About 60 percent of the latter group had received the vaccine.
Participants filled out a questionnaire with demographic information and information about their sexual activity, and were tested for 37 strains of HPV. The vaccine protects against four common strains of HPV that are known to cause warts or cancer. The strains include types 6 and 11, which cause almost all genital warts, and types 16 and 18, which cause about 70 percent of cervical cancers and 90 percent of anal cancers, said study author Dr. Jessica Kahn, associate professor of pediatrics at Cincinnati Children's Hospital Medical Center.
From 2006 to 2010, the prevalence of these four strains decreased by about 60 percent, from about 32 percent to 13 percent.
Among the vaccinated, rates of HPV infection fell from 32 percent to 10 percent -- a 70 percent drop. Perhaps even more dramatic, rates of infection among the unvaccinated fell from 30 percent to 15 percent -- a 50 percent drop.
