In the CVT, partial cross-protection against anal infection at study exit selleck kinase inhibitor was also observed in a combined analysis of HPV31, 33, or 45, for example 49.4% (95% CI: 30.3–63.6) in the full cohort [28]. Interestingly, while cross-protection against cervical infection by non-vaccine types was clearly observed in CVT women receiving three doses of Cervarix®, there was no indication

of cross-protection in those receiving two doses [27]. For instance, efficacy in the ATP cohort against 12 month persistent infection with HPV31, 33, and 45 combined was 41.3% (95% CI: 18.9–57.9) in women receiving three doses and -25.9% (95% CI: -334–66.1) in those receiving two doses. There were too few non-vaccine type infections in the women receiving one dose to meaningfully evaluate cross-protection in this group. Evidence from a long-term follow-up of a phase IIb trial of Cervarix® suggests that cross-protection might preferentially wane over time [31]. Protection from incident HPV16/18 infection remained consistently high (>90%) throughout the 6.4 years of follow-up, with a cumulative efficacy of 95.3% (95% CI: 87.3–99.6). In contrast, protection from HPV31 and HPV45 infection was 100% through the first 3 years, but then incident infections began to appear over the next 3 years, yielding cumulative efficacies of 59.8% MEK inhibitor (95% CI: 20.5–80.7)

and 77.7% (95% CI: 39.3–93.4) for HPV31 and HPV45, respectively. It will be important to evaluate in long-term field studies the public health impact of cross-protection afforded by the two vaccines. Evaluating cross-protection against disease endpoints is complicated by the fact that many

women with cervical disease are infected with more than one HPV type. Causal inferences can be made by determining the specific type(s) in a lesion biopsy or by assuming that the preceding most persistent infection is responsible for the CIN, but these approaches have limitations. Complicating the issue Methisazone is the fact that infections by HPV16 and 18, the vaccine types, tend to progress to CIN more rapidly than infections by other high-risk types [22]. Thus, in a 4-year trial, the probability that the lesion in a co-infected woman will be due to the non-vaccine type is less than the probability that it will be due to a vaccine type. A conservative approach used in the PATRICIA trial to address this issue was to evaluate cross-protection after excluding cases that were co-infected with vaccine types [30]. This exclusion consistently results in lower efficacy estimates against non-vaccines type-associated lesions. For instance, for the composite endpoint of CIN2+ associated with any of 12 non-vaccine types, efficacy in the TVC-naïve cohort was 56.2% (95% CI: 37.2–65.0) if HPV16/18 co-infections were included and a non-significant 17.1% (95% CI: -25.5–45.4) if HPV16/18 co-infections were excluded. However, the corresponding efficacies against CIN3+ were significant in both cases, 91.4% (95% CI: 65.0–99.0) and 81.9% (95% CI: 17.1–98.1), respectively.