The efficacy of HYMPAVZI was established in 116 adult and pediatric patients (aged 12 years and older and ≥35 kg) with severe hemophilia A without FVIII inhibitors or severe hemophilia B without FIX inhibitors enrolled in the BASIS study (NCT03938792), an open-label, multi-center, two-phase study. Severe hemophilia is defined as factor activity less than 1%. Patients with a history of coronary artery disease, venous or arterial thrombosis or ischemic disease were excluded from the study.

Following screening, patients entered a 6-month observation phase and were enrolled to two cohorts based on the factor replacement treatment they were receiving prior to study entry: on‑demand or routine prophylaxis. Patients who completed the observation phase were to receive 12 months of HYMPAVZI. Of the 116 patients who received HYMPAVZI, 33 patients were in the on‑demand treatment cohort and 83 were in the prophylactic treatment with FVIII or FIX cohort during the observation phase. Patients who completed the 12‑month BASIS study were eligible to enroll in an open-label extension study (NCT05145127).

Patients received an initial 300 mg loading dose of HYMPAVZI followed by maintenance doses of 150 mg of HYMPAVZI once weekly for 12 months. Dose escalation to 300 mg of HYMPAVZI once weekly was permitted after 6 months of treatment in patients weighing ≥50 kg and experiencing ≥2 breakthrough bleeds. Fourteen (12%) underwent dose escalation.

The mean annualized bleeding rates (ABRs) for treated bleeds were 38 and 7.85 in the observational phase for the on-demand and prophylaxis cohorts, respectively. All patients in the on-demand cohort had one or more target joints at study entry and 36% had 3 or more target joints at study entry. In the routine prophylaxis cohort, 57% of the patients had one or more target joints at study entry and 16% had 3 or more target joints at study entry.

The efficacy of HYMPAVZI for each cohort was based upon the ABR of treated bleeds during treatment with HYMPAVZI compared to ABR during the observational phase. Other objectives of the study included evaluation of HYMPAVZI prophylaxis on the incidences of spontaneous bleeds, joint bleeds, target joint bleeds and total bleeds.

Among the 116 patients treated with HYMPAVZI in the BASIS study, the mean age was 32 years (range 13 to 66); 19 patients were 12 to <18 years of age and all were male. Fifty-six (56) patients were White, 58 patients were Asian, 1 patient was Black or African American and 1 patient had race information unreported; 12 patients identified as Hispanic or Latino and 104 patients identified as not Hispanic or Latino. The patient population included 91 with hemophilia A and 25 with hemophilia B.

Patients with On-Demand Factor-Based Therapy in Observational Phase  
Table 3 shows the efficacy results of HYMPAVZI prophylaxis compared with on-demand factor-based therapy. HYMPAVZI prophylaxis demonstrated superiority over on-demand factor-based therapy in incidences of treated bleeds, spontaneous bleeds, joint bleeds, total bleeds and target joint bleeds.

Patients with Routine Prophylactic Factor-Based Therapy  
Table 4 shows the efficacy results of HYMPAVZI prophylaxis compared with routine prophylactic factor‑based therapy. HYMPAVZI prophylaxis demonstrated non-inferiority to routine prophylactic factor‑based therapy as measured by ABR of treated bleeds as well as incidences of spontaneous bleeds, joint bleeds, target joint bleeds and total bleeds.