ADJUVANT HPV VACCINATION IN OLDER HIV-POSITIVE MEN WHO HAVE SEX WITH MEN FOR PREVENTION OF ANAL CANCER – LONG-TERM CLINICAL AND ECONOMIC BENEFITS

Purpose: Recent data show benefits of quadrivalent human papillomavirus (qHPV) vaccination as an adjuvant/tertiary prevention strategy for prevention of anal cancer as the vaccine may decrease the hazards of recurrent high-grade squamous intraepithelial lesions (HSIL) (a precancerous lesion) in patients with history of HSIL. We evaluated the clinical and economic outcomes of adjuvant qHPV vaccination (i.e., adding qHPV vaccine to the HSIL treatment regimen) in HIV-positive MSM 27 years or older. 

Method: Using a Markov cohort model of anal carcinogenesis, we compared no qHPV vaccination after treatment for HSIL to qHPV vaccination after treatment for HSIL. Model inputs—baseline prevalence, disease transitions, costs, and utilities—were either obtained from the literature or calibrated using a separate natural history model of anal carcinogenesis. Anal carcinogenesis was conditional on patients’ CD4 count. Vaccine efficacy was defined as the reduction in the hazards of developing recurrent HSIL. The outputs were reported in terms of decrease in incidence, decrease in the lifetime risk of anal cancer after vaccination, and incremental cost-effectiveness ratio (ICER). Deterministic and probabilistic sensitivity analyses were conducted to determine the robustness of the results. Threshold analysis was performed to identify the maximum economically acceptable vaccine efficacy.

Result: Vaccination after treatment for HSIL decreased the lifetime risk of anal cancer by 63%. Vaccination was cost-saving, i.e., it resulted in an increase in quality-adjusted life years by 0.16 and a decrease in lifetime costs by $419. The predicted incidence of anal cancer after vaccination was one-third compared with no vaccination. The results were sensitive to the model parameters—progression from HGAIN to cancer, mortality attributed to anal cancer, cost of HGAIN treatment, and discount rate; however, under no alternative assumption, the willingness-to-pay threshold crossed $50,000 per QALY. To be economically acceptable (i.e., to cross the WTP threshold of $50,000 per QALY), the hazard ratio associated with vaccination is expected to be at least 0.98 for the first and subsequent years after vaccination. Probabilistic sensitivity analysis showed that vaccination was cost-effective with 100% probability at the willingness-to-pay threshold of $18,000 per QALY or more. 

Conclusion: Vaccinating HIV-positive MSM aged ≥27 after treatment for initial HSIL is a cost-saving strategy. Expansion of current vaccination guidelines to include this population sooner rather than later should be a priority.