|
|
|
By Jean Talbert, M.D.
Vaccines are one of the most effective public health interventions ever developed to protect a population against infectious disease. Smallpox has been effectively eradicated with an aggressive worldwide vaccination campaign and the morbidity and mortality rates of many other diseases such as polio, tetanus, measles, and influenza have been significantly reduced. The discovery of the human papilloma virus (HPV) as a causative agent in 99 percent of cervical cancers as well as some types of vulvar, anal and oral cancer has now opened the door to vaccination as a means of preventing cancer.
Cervical cancer is the second most common cancer among women worldwide.
Half a million women are diagnosed each year and 40 percent will die from the disease. The average age at diagnosis is 48. Pap smear screening has reduced the incidence of cervical cancer in the United States and other developed countries by 70 percent, but millions of health care dollars are still spent each year on the treatment of dysplasia, a precancerous change of the cervix.
There are over 100 types of HPV, divided into high and low risk types. Low-risk type infections typically cause benign warts in a specific region of the body. Types 1 and 2 cause warts on hands and feet, types 6 and 11 cause genital warts or condyloma.
So far, 15 types of HPV have been associated with cervical cancer, with types 16 and 18, the most common high risk types, being associated with 70 percent of cervical cancer worldwide. These are transmitted by sexual contact.
Between 70 to 80 percent of sexually active adults in this country will have acquired at least one type of genital HPV infection by age 50. Condoms are not completely protective as the virus lives in the skin of the genital tract and is transmitted by skin to skin contact. Most infections are asymptomatic. Fortunately, most infections are transient and the virus is suppressed over time by a healthy human immune system. Ten to 20 percent of infections by high risk virus types are persistent and present the greatest risk of cervical cancer.
Tobacco use and immune deficiency, such as HIV infection, significantly increase the risk of persistent infection and, subsequently, the development of cancer.
Pap smear screening is a very effective way to identify persistent infection. Women with abnormal Paps are referred for colposcopy, a microscopic exam of the cervix where biopsies are taken. Significant abnormalities (moderate or severe dysplasia) are then treated surgically with excisional biopsies. Unfortunately, many women experience significant psychosocial distress while undergoing these procedures and may face an increased risk of miscarriage or preterm labor in subsequent pregnancies.
Prevention of cervical cancers and precancers is a primary public health goal worldwide. Educating the public about the sexual transmission of genital HPV and the avoidance of high risk behavior is crucial. Delaying the onset of sexual activity, avoiding multiple partners and consistent use of condoms will help to reduce the prevalence of the disease but will not eliminate it. Vaccination against HPV infection prior to the onset of sexual activity is a tremendous advance that should help to protect future generations.
One HPV vaccine is available here although others are on the horizon.
Gardasil is the vaccine that has proved effective against the four types of HPV that cause 70 percent of cervical cancer and 90 percent of genital warts worldwide. The vaccine is derived from the protein coat of the virus so it is incapable of causing disease itself.
Side effects occur in less than 5 percent of cases and include pain at the injection site and fever. Serious side effects such as difficulty breathing are rare. Studies show that the vaccine prevents 98 percent of precancers and 100 percent of genital warts. Immunity is maintained for at least five years.
Gardasil currently is licensed for all girls and women between ages 9 and 26. The target age is 11-12 so that the three doses of vaccine can be completed well before sexual activity begins. The vaccine will not treat disease in women who already have acquired a particular virus, but may protect them against other types to which they have not yet been exposed. Routine Pap screening is still advised after vaccination, as the current vaccine does not protect against all forms of high risk HPV.
Some questions regarding the vaccine are still unanswered, particularly, will booster shots be required and should boys and men be vaccinated. Men clearly carry HPV, but the risk of serious disease in males is low. However, vaccinating both men and women would be much more effective.
New generations of vaccine are likely to protect against even more types of HPV. Overall, the current HPV vaccine appears to be safe and effective and should be encouraged for most young women.
(Dr. Talbert is a board certified OB/GYN specialist practicing with Cape Obstetrics, Midwifery & Gynecology in Falmouth and Sandwich, 508-457-0088.)