How do HPV vaccines work?

The HPV vaccines work like other immunizations that guard against viral infections. The investigators hypothesized that the unique surface components of HPV might create an antibody response that is capable of protecting the body against infection, and that these components could be used to form the basis of a vaccine.

The HPV surface components can interact with one another to form virus-like particles (VLP) that are not infectious, because they lack DNA.

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However, these VLPs can attach to cells and stimulate the immune system to produce antibodies that can prevent the complete papillomavirus, in future encounters, from infecting cells.

Although HPV vaccines can help prevent future HPV infection, they do not help eliminate existing HPV infections.

How effective are the HPV vaccines?

Gardasil and Cervarix are highly effective in preventing infection with the types of HPV they target. The vaccines have been shown to provide protection against persistent cervical HPV 16/18 infections for up to 8 years, which is the maximum time of research follow-up thus far. More will be known about the total duration of protection as research continues.7

HPV vaccination has also been found to prevent nearly 100% 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.7–10

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.11

Both Gardasil and Cervarix are designed to be given to people in three doses over a 6-month period. However, a recent study showed that women who received only two doses of Cervarix had just as much protection from persistent HPV 16/18 infection as women who received three doses, and the protection was observed through 4 years of follow up.12

Even one dose provided protection; however, these findings need to be evaluated with more research to determine whether fewer than three doses of the vaccine will provide adequate duration of protection. Nonetheless, this information may be helpful for public health officials who administer vaccination programs among groups of people unlikely to complete the three-dose regimen.