Partial HPV Vaccine Series & Girls' Genital Warts
But Swedish study didn't address more critical issue of cervical cancer prevention
By Steven Reinberg
TUESDAY, Feb. 11, 2014 (HealthDay News) -- Girls given two doses of the human papillomavirus (HPV) vaccine instead of the recommended three doses appear to have some protection against genital warts, Swedish researchers report.
Whether two doses is enough to protect against cervical cancer, however, isn't known and experts remain wary of partial vaccination since the primary goal of the vaccine is to protect women from this potentially deadly cancer.
"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.
Arnheim-Dahlstrom cautioned that they did not study the vaccine's effectiveness in preventing cervical cancer. "The take-home message is to stick to the recommended dose schedule until other recommendations are made," she said.
The report was published in the Feb. 12 issue of the Journal of the American Medical Association.
Dr. Mark Messing, a gynecologic oncologist at Texas Oncology, an affiliate of the U.S. Oncology Network, said, "HPV infection can cause genital warts and cancer of the lower female genital tract, including the cervix, vulva, vagina, as well as cancer of the anus, tongue and throat."
While there are more than a hundred different subtypes of the virus, only a few are considered high-risk, he explained. Two vaccines -- Cervarix and Gardasil -- are available against the two most common types of HPV that cause cervical cancer and some other types of cancer. Gardasil also covers the two most common HPV strains that cause genital warts. Both vaccines are given in three injections over six months.
The incubation time for a genital wart infection is only about one to six months after exposure, compared with the 10 to 20 years usually needed for cancer to develop after HPV infection, Messing said.
"This study does not provide any information on how effective two versus three doses of vaccine will be in preventing the more serious disease of cervical or other cancer," he 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.