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HPV Vaccine Reduces Cervical Abnormalities

Vaccination of young women in Australia against human papillomavirus (HPV) lowered incidence of serious cervical cell abnormalities and early cervical cancer by nearly 40%.

Human papillomavirus is common among men and women worldwide. HPV infection triggers abnormal cell growth; many types cause warts, while high-risk types including 16 and 18 can cause cancer of the cervix, genital-anal region, or mouth and throat.

Gardasil (made by Merck), a quadrivalent vaccine that protects against HPV types 6, 11, 16, and 18, was approved in the U.S. after large clinical trials showed it reduced the risk of cervical cancer. Initially approved for young women age 9-26 years, its indication was later extended to young men, who are susceptible to anal and genital cancer.

Since people are typically infected with HPV soon after they become sexually active, vaccination is recommended starting around the time of puberty, but people can get a "catch up" vaccine into their twenties. However it is not recommended for older people who are likely to have already acquired HPV.

As described in the June 18, 2011, issue of The Lancet, Julia Brotherton from the Victorian Cytology Service and colleagues looked at trends in cervical abnormalities among women in Victoria, Australia, before and after introduction of the quadrivalent HPV vaccination program for all women age 12-26 years, starting in 2007.

The researchers analyzed data from the Victorian Cervical Cytology Registry collected between 2003 and 2009, comparing the incidence of high-grade and low-grade cytological cervical abnormalities among 5 age groups during 2 periods before and after the vaccination program began (January 2003-March 2007 and April 2007-December 2009).

High-grade abnormalities (HGAs) included cervical intraepithelial neoplasia of grade 2 or higher and carcinoma in situ (localized); low-grade abnormalities included milder cell changes.

Results

• The incidence of high-grade abnormalities decreased by 38% among girls younger than 18 after introduction of the vaccination program.
• The incidence of HGAs among women under 18 fell from 0.8% during the pre-vaccination period to 0.4% during the entire post-vaccination period, and further to 0.2% in 2009.
• The decrease started soon after the vaccine program began.
• This decrease was progressive over time and significantly departed from the prevailing trend of rising incidence.
• No similar significant decline in incidence of serious abnormalities was seen for women in older age groups.
• However, incidence of abnormalities appeared to fall among women age 18-20 starting about 1.5 years after vaccine introduction, though this did not reach statistical significance.
• No significant decrease in incidence of LGAs was observed in any age group.

"This is the first report of a decrease in incidence of HGAs within 3 years after the implementation of a population-wide HPV vaccination programme," the study authors concluded.

They added, "Our finding that the decrease in HGA incidence occurred in the youngest vaccination cohort before it occurred in the older, catch-up cohorts (who were more likely to have been previously sexually experienced) reinforces the appropriateness of the targeting of prophylactic HPV vaccines to pre-adolescent girls."

Investigator affiliation: Victorian Cytology Service Registries, Victorian Cytology Service, East Melbourne, Victoria, Australia.

7/5/11

Reference
J Brotherton, M Fridman, CL May, et al. Early effect of the HPV vaccination programme on cervical abnormalities in Victoria, Australia: an ecological study. Lancet 377(9783):2085-92 (abstract). June 18, 2011.