End-of-trial results from a trial testing Cervarix, a vaccine against human papillomavirus (HPV) types 16 and 18, showed that the vaccine continued to provide substantial protection against cervical precancers 4 years after vaccination. Cervarix provided almost complete protection in young women who had no evidence of exposure to HPV at the time of vaccination. The vaccine provided less protection for the total vaccinated cohort and was less effective with increasing age at vaccination. These findings reflect the vaccine’s lack of effectiveness against infections acquired before vaccination.
The vaccine also partially protected women against four types of HPV that are not targeted by the vaccine. (Although HPV-16 and -18 cause about 70 percent of cervical cancers worldwide, as many as 15 HPV types can cause cancer.) These results from the PATRICIA trial (Papilloma Trial against Cancer in Young Adults) were published online November 9 in Lancet Oncology in two separate papers, available here and here.
The PATRICIA trial enrolled 18,644 young women between the ages of 15 and 25 from 14 countries. The participants were randomly assigned to receive either three doses of Cervarix or three doses of a hepatitis A vaccine as a control. Results from the interim analysis, published in July 2009, showed that the vaccine greatly reduced the risk of grade 2 cervical intraepithelial neoplasias and higher (CIN2+).
The new analysis shows that, 4 years after vaccination, Cervarix provided complete protection against grade 3 cervical intraepithelial neoplasias or higher (CIN3+) associated with HPV-16 and -18 among women who had no evidence of exposure to HPV. The vaccine provided strong protection against CIN3+ caused by other HPV types in this same group of women. Among the total cohort of women who received at least one dose of Cervarix, some of whom may have had prior exposure to HPV, the vaccine provided some protection. (See the table below.)
Cervarix Vaccine Efficacy among Women Who Received at Least One Dose of Cervarix
|Women with no evidence of HPV exposure at baseline||Women who may have had prior exposure to HPV|
|Against CIN3+ associated with HPV-16 and -18||100 percent||45.7 percent|
|Against all CIN3+, regardless of HPV type||93.2 percent||45.6 percent|
|Against all adenocarcinoma in situ||100 percent||76.9 percent|
The vaccine provided cross-protection against HPV-33, HPV-31, HPV-45, and HPV-51, all cancer-causing types of the virus. The researchers speculate that the observed cross-protection may be due either to the vaccine adjuvant (a substance that stimulates the immune system) or to similarities among proteins found on the surfaces of different HPV types.
In an accompanying editorial, Drs. Mark Schiffman and Sholom Wacholder of NCI’s Division of Cancer Epidemiology and Genetics, who were involved with the NCI Costa Rica HPV vaccine trial, noted the importance of the PATRICIA trial results. They also stated that “the practical aspects of vaccine uptake are now the most important issue in HPV vaccine research from a public health perspective.” To increase vaccine uptake in the developing world, where 90 percent of cervical cancer cases occur, next-generation HPV vaccines will need to be less expensive, provide protection in a single dose, and/or be stable without refrigeration, they explained.