Both Gardasil and Cervarix have been shown to prevent cervical dysplasia from the HPV strains that they target, that is, types 16, 18, 6, and 11 for Gardasil and types 16 and 18 for Cervarix. This effect has lasted 4 years after vaccination for Gardasil and more than 6 years for Cervarix. As of September 2010, it is thought that booster vaccines will not be necessary.
The vaccines also offer some protection against a few high-risk HPV types that are closely related to HPVs 16 and 18. Cervarix has been shown to offer some protection against types 45 and 31, similarly, Gardasil has been shown to offer some protection against type 31, and 9 others. However, there are other high-risk HPV types that are not affected by the vaccines.
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. Neither of these HPV vaccines has been proven to provide complete protection against persistent infection with other HPV types, although some initial results suggest that both vaccines might provide partial protection against a few additional HPV types that can cause cervical cancer. 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 vaccination has also been found to prevent nearly 100 percent of the precancerous cervical cell changes that would have been caused by HPV 16/18. The data so far show duration of production for up to 6.4 years with Cervarix and for up to 5 years for Gardasil—in women who were not infected with HPV at the time of vaccination.
Both Gardasil and Cervarix have been tested in tens of thousands of people in the United States and many other countries. Thus far, no serious side effects have been shown to be caused by the vaccines. The most common problems have been brief soreness and other local symptoms at the injection site. These problems are similar to ones commonly experienced with other vaccines. The vaccines have not been sufficiently tested during pregnancy and, therefore, should not be used by pregnant women.