What Is HPV?
HPV stands for Human Papilloma Virus. There are over 100 different types of HPV viruses that have been around for hundreds of years. HPV is a virus that lives in skin cells. Most of the time HPV goes away without any kind of treatment. The body's natural defense system (immune system) will usually suppress or eliminate the virus, much like how the body gets rid of a common cold (colds are also caused by viruses). In a study of college women, the median duration of HPV infection was 8 months.
Some types of the HPV virus can infect the genital epithelial cells (skin and mucous membranes). Some types of HPV virus cause warts that appear on the genitals (vagina, vulva, penis, etc.) and anus of women and men.
How Common Is An HPV Infection?
According to the Centers for Disease Control and Prevention (CDC), an estimated 6.2 million new HPV infections occur every year in the United States among persons aged 14-44. Of these, 74% occur among those aged 15-24. The CDC estimates that over 80% of sexually active women will have acquired genital HPV by age 50. Most women are unaware they are infected with HPV because HPV does not usually cause any symptoms. Both heterosexual and lesbian women can get HPV. However, while HPV is extremely common in young women it is usually cleared by a woman's own immune system. Most people become negative for HPV within 6 to 24 months after their first positive result. During 24 months of follow-up, 92% of women who tested positive for HPV became negative.
What Is The Concern Of HPV?
Some of the types of the virus that are sexually transmitted can cause women to have abnormal pap smears. Most women discover they have HPV when they have a pap smear with abnormal results. If abnormal cells are found on a woman's Pap smear, most Pap smear laboratories will perform an HPV DNA test to see if HPV is present. This can be done without an additional visit to the clinic or doctor's office.
Of the more than 100 types of HPV that have been identified, approximately 25 play a role in infection of the anogenital tract. These types are classified into two relative risk categories, low and high. The low-risk viruses in HPV types are 6, 11, 42, 43 and 44. These are often not even reported back on pap smear/HPV DNA results. HPV 6 and 11 are the most common indicators of genital warts (condylomata). The high-risk types, 31, 33, 35, 39, 51 and 52 can be associated with cervical cancer, although this occurs less frequently than with other high-risk types. The high-risk types that are more commonly associated with cervical cell abnormalities are 16, 18, 45 and 58. But it is important to remember that most high-risk HPV exposure does not lead to cancer.
Does HPV Cause Cancer?
Although infection with a high-risk HPV type is considered necessary for the development of cervical cancer, the majority of women with high-risk HPV infection do not develop cancer. Long-term persistence of the virus is necessary for cancer to develop. This usually takes 10 to 20 years. When HPV persists and does not go away, there are usually other factors that inhibit the body's natural defense system from doing its job. Some factors that may affect a body's ability to fight HPV infection are smoking, HIV and other diseases that weaken the immune system, cancer treatments such as chemotherapy, previous Chlamydia or herpes infection, poor nutrition, inability to get health care due to poverty, five or more vaginal births and prolonged use of birth control pills (5 years or longer). High-risk HPV is the most common type found in young women with mild abnormal cells and usually does not cause cancer. Only 10-20% of women do not have an adequate immune response to HPV exposure.
HPV can cause abnormal Pap smear results because HPV is a virus which infects skin cells. When HPV infects the skin cells in the cervix it can cause the cells to change and become abnormal. There other reasons beside HPV for abnormal Pap smear results such as infection. The incidence of cervical cancer in the US is about 15 per 100,000 women, relatively low as compared to 140 per 100,000 incidences of breast cancer, according to the National Cancer Institute.
The HPV Vaccine
In July of 2006, the FDA approved an HPV vaccine, named Gardasi1®. It is recommended for use in women ages 9-26. Gardasil is effective for only 4 HPV viruses. A second vaccine, Cervarix, is expected to be submitted for review by the Food and Drug Administration (FDA) this year. This vaccine is effective for only 2 HPV viruses.
How Effective Is The HPV Vaccine?
In clinical studies conducted by the vaccine manufacturers, the HPV vaccines have been demonstrated to be 98 percent effective in preventing infection with HPV types 16 and 18 in women who have not previously been infected with these two strains of the virus. The effectiveness went down to 44 percent in women previously infected with types 16 and 18 and was only 17 percent effective when all HPV types were taken into account. It is also important to know there are other HPV viruses, not protected by the vaccine, that cause approximately 30 percent of cervical cancers.
Additionally, the vaccine has no value in eliminating pre¬existing HPV infection or in treating HPV disease. Currently, there are no data on the effectiveness of the vaccine in men or in women over 26 years of age.
How Safe Is The HPV Vaccine?
Because Gardasil is a new vaccine, the long term effects are still not known. Continuing studies to evaluate the effectiveness, length of protection, and long-term safety are still being done. In a recent editorial in the New England Journal of Medicine, two University of California—San Francisco doctors stated they are concerned there are still too many questions about the effectiveness, length of protection, and long-term safety of the vaccine. Trials on the effectiveness of the vaccine on boys and men are also under way. Results are expected later this year.
How Long Does Immunity Last?
The duration of immunity is not known. Some studies showed protection for up to five years. It is also not yet known if booster doses will be needed in the future.