An experimental vaccine against a high-risk type of human papillomavirus (HPV16) reduces the risk of persistent infection with HPV16 and, more importantly, reduces the risk of HPV16-related precancerous changes to the cervix. These results were published in Obstetrics and Gynecology.
Human papillomavirus (HPV) is a sexually transmitted infection that is the primary cause of cervical cancer. Different types of HPV are classified as “low-risk” or “high-risk” based on how likely they are to cause cervical cancer. While several types of HPV have been linked with cervical cancer, HPV types 16 and 18 appear to pose the greatest risk.
Recent research in the area of cervical cancer has focused on screening women for specific types of HPV and on developing an HPV vaccine to prevent cervical cancer. Early results from vaccine studies have been promising; researchers continue to follow subjects in order to assess longer-term outcomes.
An important outcome for HPV vaccine studies is cervical intraepithelial neoplasia (CIN). CIN refers to a range of precancerous changes to the cervix that may progress to cervical cancer. The severity of CIN is classified on a scale of 1 to 3, with 3 being the most severe. Vaccines that reduce the risk of high-grade CIN (grades 2 or 3) are likely to reduce the risk of cervical cancer.
To evaluate the effect of an experimental HPV16 vaccine (HPV16 L1 VLP) on risk of CIN 2 and CIN 3, researchers evaluated data from a large clinical trial. The trial enrolled 2,391 women between the ages of 16 and 23 years. Half the women were given the HPV16 L1 VLP vaccine, and half received a placebo. The vaccine was given at day 1, month 2, and month 6 after the start of the study. Study participants have now been followed for four years.
- None of the vaccinated women developed HPV16-related CIN 2 or CIN 3.
- 12 of the women in the placebo group developed HPV16-related CIN 2 or CIN 3.
- There were 7 cases of persistent HPV16 infection among the vaccinated women.
- There were 111 cases of persistent HPV16 infection among women in the placebo group.
Among women who were vaccinated, serum antibodies against HPV16 peaked at month seven, declined through month 18, and were fairly stable between months 30 and 48.
The researchers conclude that the vaccine reduces the risk of persistent HPV16 infection, and also protects against precancerous changes to the cervix caused by HPV16. The protection lasts for at least 3½ years after vaccination. The researchers note that use of this vaccine would likely reduce the risk of cervical cancer.
Reference: Mao C, Koutsky LA, Ault KA et al. Efficacy of Human Papillomavirus-16 Vaccine to Prevent Cervical Intraepithelial Neoplasia. Obstetrics and Gynecology. 2006;107:18-27.