The accuracy of baseline viral load for predicting the efficacy of elbasvir/grazoprevir in participants with hepatitis C virus genotype 1a infection: An integrated analysis

European treatment guidelines for hepatitis C virus (HCV) infection recommend that people with genotype (GT) 1a infection and baseline viral load ≤800 000 IU/mL receive elbasvir/grazoprevir (EBR/GZR) for 12 weeks, and those with baseline viral load >800 000 IU/mL receive EBR/GZR plus ribavirin for 16 weeks. This analysis was conducted to clarify whether baseline viral load can serve as an accurate, sensitive or specific stratification factor for defining EBR/GZR regimens. In this post hoc, integrated analysis, participants with GT1a infection who received EBR 50 mg/GZR 100 mg for 12 weeks were stratified according to baseline viral load. Sustained virologic response at 12 weeks post‐treatment was achieved by 95.2% (911/957) of participants and was higher among participants with baseline viral load ≤800 000 IU/mL vs >800 000 IU/mL (98.5% vs 93.9%). The 800 000 IU/mL threshold had a positive predictive value of 98.5%, a negative predictive value of 6.1%, a specificity of 91.3%, a sensitivity of 28.4% and an overall accuracy of 31.5%. A baseline viral load cutpoint of 800 000 IU/mL had high positive predictive value and specificity but poor negative predictive value, sensitivity and accuracy in predicting treatment outcomes in this population. Baseline NS5A resistance‐associated substitutions (RASs) were detected in 25% (1/4) of virologic failures with baseline viral load ≤800 000 IU/mL and 59.5% (25/42) of those with baseline viral load >800 000 IU/mL. Overall, these data suggest that, compared with the use of a baseline viral load cutpoint, baseline testing for NS5A RASs enables more individuals to receive the 12‐week EBR/GZR regimen without compromising the opportunity for SVR.