HPV vaccine may be linked to declining genital warts

A few strains of human papillomavirus (HPV) are the major cause of cervical cancer (16 and 18) and the cause of most genital warts (6 and 11). In the U.S., some young women started using a vaccine—Gardasil—that protects against all four of these HPV strains in 2006. Clinical trials showed that the vaccine conferred high levels of protection from HPV to an individual woman, but we are still awaiting evidence regarding a population-level effect of the vaccine. Because cervical cancer usually develops many years after a woman first contracts a high-risk strain of HPV, it will be at least a decade before we can assess the vaccine's impact on cancer incidence and mortality rates.

Genital warts are usually on a much faster timeline than cervical cancer—they develop within a few weeks or months after exposure to the HPV strains that cause them. A new study from the California Department of Public Health's (CADPH) Sexually Transmitted Disease Control Branch assessed the incidence of genital warts in California Family PACT clients over four years, 2007-2010. UCSF Bixby Center members and study authors Drs. Heidi Bauer and Joan Chow showed a significant decline in the number of genital warts diagnoses for women and men under age 26. The ecological study used billing data from over 8 million Family PACT clients, and further found no change or slight increases in the number of genital warts diagnoses for clients age 26 and over. An ecological study cannot assess a causal relationship between the observed declines in genital warts and use of the quadrivalent vaccine, but it does provide interesting insight to the dynamics of HPV infection in a large population.