Cervical Cancer Prevention Should Focus On Vaccination
The cost-effectiveness of vaccination in the United States against human papillomavirus (HPV), a sexually-transmitted virus that causes cervical cancer, will be optimized by achieving universal vaccine coverage in young adolescent girls, by targeting initial "catch-up" efforts to vaccinate women younger than 21 years of age, and by revising current screening policies, according to an analysis by Harvard School of Public Health (HSPH) researchers in the August 21, 2008 issue of The New England Journal of Medicine.
In the U.S. in 2007, cervical cancer developed in more than 11,000 women and killed 3,600 women. Cervical cancer is caused by infection with high-risk "oncogenic" types of HPV, also associated with other cancers. Worldwide, HPV types 16 (HPV-16) and 18 (HPV-18) cause approximately 70% of cervical cancer cases. Vaccines against HPV-16 and HPV-18 appear to be highly efficacious in preventing HPV-16 and HPV-18 infections and cervical disease in females who have not previously been infected with these types. The quadrivalent vaccine currently licensed in the U.S. also prevents low risk HPV types 6 and 11 (HPV-6 and HPV-11) infections, which are responsible for most genital warts and juvenile-onset recurrent respiratory papillomatosis (JORRP), a rare but severe respiratory condition usually diagnosed in infancy that may be related to a mother's infection with genital warts.
Cervical cancer prevention in the U.S. has traditionally relied on a screening program involving frequent cytology (Pap smear) and/or HPV DNA testing, recommended annually or biennially for sexually-active women. HPV vaccination raises questions regarding the age at which to vaccinate females, target groups for temporary catch-up programs, and appropriate changes to screening practices.
Jane Kim, assistant professor of health decision science in the Department of Health Policy and Management at HSPH, led the study which involved synthesizing epidemiologic, clinical, and demographic information using sophisticated computer models that simulate the U.S. population. The models were used to predict the health and economic outcomes of HPV vaccination of preadolescent girls (i.e., 12 years of age) and catch-up vaccination over a 5-year period for girls and women over 12 years of age, in the context of routine cervical cancer screening; strategies differed in the upper age of catch-up programs, to ages 18, 21, or 26 years. While the study focused on the prevention of cervical disease, the investigators also examined the benefits of the quadrivalent vaccine on genital warts and possible benefits of averting other HPV-related cancers and JORRP.
A novel part of this study involved examining how uncertain scenarios might impact the appropriate policies for the U.S., such as the duration of vaccine protection and whether or not a booster dose will be needed, whether or not the vaccine will also prevent infections with other HPV types, and what might occur to rates of cancer if women change their screening practices after being vaccinated.
Kim and co-author Sue Goldie, professor of health decision science at HSPH, found that vaccination against HPV-16 and HPV-18 would lead to lower cervical cancer rates and be economically attractive if high coverage can be achieved in the most important target group of 12-year-old girls, and if vaccine protection against infection lasted for at least 20 years. The study predicted that if most 12-year-old girls were vaccinated, their future cervical cancer screening could begin somewhat later than currently recommended and be conducted less frequently (i.e., every 3 to 5 years).