Infectious enthusiasm

The sexually transmitted human papillomavirus (HPV) is associated with 50% of cervical cancer cases and is considered to be a potent human carcinogen. In the New England Journal of Medicine, Laura Koutsky and colleagues show that a vaccine that prevents persistent HPV16 infection can also reduce the incidence of cervical cancer.

In this double-blind study, 768 women of ages 16–23 received three doses of an HPV16 vaccine that consists of virus-like particles — viral coats without the DNA component. A total of 765 other women received a placebo control and the women were followed for a median of 17.4 months after completing the vaccination regimen.

Some 41 cases of HPV16 infection occurred in the placebo group, and these included nine cases of virus-related cervical intaepithelial neoplasia. Amazingly, none of the women that received the vaccine developed persistent HPV16 infections or virus-associated cervical neoplasia. The vaccine is therefore 100% effective in protecting women from HPV16 and preinvasive cancer. It was also well-tolerated and the immunized women generated high levels of antibodies against the virus.

HPV vaccines are urgently needed, as cervical cancer ranks second as a cause of cancer-related deaths in women. More than 450,000 cases are diagnosed each year worldwide, and therapeutic approaches are limited. Although the incidence of this cancer has been reduced by screening, 50% of cervical cancers that occur in the United States develop in women who have been screened. Furthermore, many women in developing countries do not have access to screening programmes. A safe and effective HPV vaccine could therefore overcome these obstacles to cervical cancer prevention. There is no evidence, however, that this vaccine will reverse cervical cancer once it has developed.

Nearly 20 different types of HPV have been associated with cervical cancer, and Koutsky et al. show that vaccination against one will not protect against another. Similar vaccination approaches might be developed to prevent the spread of these other viruses. The task is not as overwhelming as it seems, as only five HPVs — types 16, 18, 31, 33 and 45 — are responsible for most cervical cancer cases. In an accompanying editorial, Christopher P. Crum (Brigham and Women's Hospital, Boston) predicts that widespread vaccination against these five strains could reduce the number of cervical cancer deaths by 95%. ORIGINAL RESEARCH PAPER Koutsky, L. A. et al. A controlled trial of a human papillomavirus type 16 vaccine. N. Engl. J. Med. 21, 1645–1650 (2002)