HPV Vaccine - Efficacy

Efficacy

Both Gardasil and Cervarix have been shown to prevent cervical dysplasia from the high-risk HPV types 16 and 18 and some protection against a few closely related high-risk HPV types. However, there are other high-risk HPV types that are not affected by the vaccines. The protection against HPV 16 and 18 has lasted 5 years after vaccination for Gardasil and more than 6 years for Cervarix. It is thought that booster vaccines will not be necessary.

Gardasil also protects against low-risk HPV types 6 and 11, which do not cause cancer, but do cause genital warts.

A recent analysis of data from a clinical trial of Cervarix found that this vaccine is just as effective at protecting women against persistent HPV 16 and 18 infection in the anus as it is at protecting them from these infections in the cervix. Overall, about 30 percent of cervical cancers will not be prevented by these vaccines. Also, in the case of Gardasil, 10 percent of genital warts will not be prevented by the vaccine. Neither vaccine prevents other sexually transmitted diseases, nor do they treat HPV infection or cervical cancer.

HPV types 16, 18 and 45 contribute to 94% of cervical adenocarcinoma (cancers originating in the glandular cells of the cervix). While most cervical cancer arises in the squamous cells, adenocarcinomas make up a sizable minority of cancers. Further, Pap smears are not as effective at detecting adenocarcinomas, so where Pap screening programs are in place, a larger proportion of the remaining cancers are adenocarcinomas. Trials suggest that HPV vaccines may also reduce the incidence of adenocarcinoma.