Author response: Efficacy of ultra-short, response-guided sofosbuvir and daclatasvir therapy for hepatitis C in a single-arm mechanistic pilot study

Abstract

Article Figures and data Abstract Editor's evaluation eLife digest Introduction Methods Results Discussion Appendix 1 Data availability References Decision letter Author response Article and author information Metrics Abstract Background: World Health Organization has called for research into predictive factors for selecting persons who could be successfully treated with shorter durations of direct-acting antiviral (DAA) therapy for hepatitis C. We evaluated early virological response as a means of shortening treatment and explored host, viral and pharmacokinetic contributors to treatment outcome. Methods: Duration of sofosbuvir and daclatasvir (SOF/DCV) was determined according to day 2 (D2) virologic response for HCV genotype (gt) 1- or 6-infected adults in Vietnam with mild liver disease. Participants received 4- or 8-week treatment according to whether D2 HCV RNA was above or below 500 IU/ml (standard duration is 12 weeks). Primary endpoint was sustained virological response (SVR12). Those failing therapy were retreated with 12 weeks SOF/DCV. Host IFNL4 genotype and viral sequencing was performed at baseline, with repeat viral sequencing if virological rebound was observed. Levels of SOF, its inactive metabolite GS-331007 and DCV were measured on days 0 and 28. Results: Of 52 adults enrolled, 34 received 4 weeks SOF/DCV, 17 got 8 weeks and 1 withdrew. SVR12 was achieved in 21/34 (62%) treated for 4 weeks, and 17/17 (100%) treated for 8 weeks. Overall, 38/51 (75%) were cured with first-line treatment (mean duration 37 days). Despite a high prevalence of putative NS5A-inhibitor resistance-associated substitutions (RASs), all first-line treatment failures cured after retreatment (13/13). We found no evidence treatment failure was associated with host IFNL4 genotype, viral subtype, baseline RAS, SOF or DCV levels. Conclusions: Shortened SOF/DCV therapy, with retreatment if needed, reduces DAA use in patients with mild liver disease, while maintaining high cure rates. D2 virologic response alone does not adequately predict SVR12 with 4-week treatment. Funding: Funded by the Medical Research Council (Grant MR/P025064/1) and The Global Challenges Research 70 Fund (Wellcome Trust Grant 206/296/Z/17/Z). Editor's evaluation Hepatitis C virus (HCV) infection continues to be a global public health problem with over 70 million infected. The current study provides a response to the WHO call for identifying patients with HCV who could be successfully treated with a shorter duration of direct-acting antiviral (DAA) therapy. It provides valuable knowledge to the ongoing research to shorten DAA therapy duration while maintaining high cure rates. Such efforts would impact both treatment access and achieving WHO elimination goals for HCV. https://doi.org/10.7554/eLife.81801.sa0 Decision letter Reviews on Sciety eLife's review process eLife digest Hepatitis C is a blood-borne virus that causes thousands of deaths from liver cirrhosis and liver cancer each year. Antiviral therapies can cure most cases of infection in 12 weeks. Unfortunately, treatment is expensive, and sticking with the regimen for 12 weeks can be difficult. It may be especially challenging for unhoused people or those who use injection drugs and who have high rates of hepatitis C infection. Shorter durations of therapy may make it more accessible, especially for high-risk populations. But studies of shorter antiviral treatment durations have yet to produce high enough cure rates. Finding ways to identify patients who would benefit from shorter therapy is a key goal of the World Health Organization. Potential characteristics that may predict a faster treatment response include low virus levels before initiating treatment, patient genetics, drug resistance mutations in the virus, and higher drug levels in the patient's blood during treatment. For example, previous research showed that a rapid decrease in virus levels in a patient's blood two days after starting antiviral therapy with three drugs predicted patient cures after three weeks of treatment. To test if high cure rates could be achieved in just four weeks of treatment, Flower et al. enrolled 52 patients with hepatitis C in a study to receive the most widely accessible dual antiviral treatment (sofosbuvir and daclatasvir). Participants received four or eight weeks of treatment, depending on the amount of viral RNA in their blood after two days of treatment. The results indicate that a rapid decrease in virus levels in the blood does not adequately predict cure rates with four weeks of two-drug combination therapy. However, eight weeks may be highly effective, regardless of viral levels early in treatment. Thirty-four individuals with low virus levels on the second day of treatment received four weeks of therapy, which cured 21 or 62% of them. All seventeen individuals with higher viral levels on day two were cured after eight weeks of treatment. Twelve weeks of retreatment was sufficient to cure the 13 individuals who did not achieve cure with four weeks of therapy. Even patients with drug resistance genes after the first round of therapy responded to a longer second round. Flower et al. show that patient genetics, virus subtype, drug levels in the patient's blood, and viral drug resistance genes before therapy, were not associated with patient cures after four weeks of treatment. Given that retreatment is safe and effective, larger studies are now needed to determine whether eight weeks of therapy with sofosbuvir and daclatasvir may be enough to cure patients with mild liver disease. More studies are also necessary to identify patients that may benefit from shorter therapy durations. Finding ways to shorten antiviral therapy for hepatitis C could help make treatment more accessible and reduce therapy costs for both individuals and governments. Introduction Direct-acting antiviral (DAA) therapy for hepatitis C (HCV) offers high cure rates to those able to adhere to standard durations of treatment. In low- and middle-income countries, where treatment is limited to second-generation NS5A/NS5B-inhibitor combinations, standard treatment is at least 12 weeks. This duration presents a barrier to successful engagement in care for some populations (Kracht et al., 2019; Petersen et al., 2016), hampering the elimination of HCV as a public health threat. Novel treatment strategies are required for hard-to-reach individuals such as people who inject drugs and those of no fixed abode. In Vietnam, DAA therapy remains prohibitively expensive for many of those infected. A standard 12-week course of sofosbuvir and daclatasvir (SOF/DCV) was priced at US$2417–2472 in Ho Chi Minh City (HCMC) in 2019 (Nguyen Thanh et al., 2019). Despite the government subsidising 50% of drug costs since, the Ministry of Health estimates only 1000 individuals accessed DAA treatment through health insurance in 2019, and 2700 in 2020 (Ministry of Health V, 2021). The World Health Organization has called for research into predictive factors for selecting persons who could be successfully treated with shorter durations of therapy (World Health Organization, 2018), which could expand access to treatment and reduce drug costs. Studies evaluating short-course therapy are challenging for infectious diseases where there are significant clinical risks of failure (e.g., TB and sepsis). However, HCV provides a model where treatment failures can be successfully retreated (Cooke and Pett, 2021) allowing exploration of mechanisms underlying successful therapy. Shortened DAA therapy is associated with disappointing rates of cure, such that it could never be recommended routinely. A systematic review and meta-analysis into treatment optimisation for HCV with DAA therapy in individuals with favourable predictors of response, found that pooled sustained virological response (SVR) for regimens of ≤4 weeks duration was 63.1% (95% confidence interval [CI] 39.9–83.7), 6 weeks duration was 81.1% (75.1–86.6) and 8 weeks duration was 94.2% (92.3–95.9) (Jones et al., 2019). However improved rates of cure were seen with an increased number of individual-level factors known (or assumed) to be favourable, such as non-genotype 3 infection, lower body mass index (BMI), lower baseline viral load, mild liver disease, absence of prior treatment failure and a rapid virological response to treatment (Jones et al., 2019). Rapid virological response offers a promising means of shortening treatment duration while maintaining high rates of cure. So-called response-guided therapy (RGT), whereby antiviral duration is shortened in individuals who rapidly suppress virus levels in blood after starting treatment, was routinely used in the era of interferon-based therapy, when an undetectable HCV RNA at 4 weeks was used to determine a shorter course of pegylated interferon and ribavirin (Fried et al., 2011). Evidence supporting RGT with DAAs at earlier time points is emerging (Cooke and Pett, 2021; Lau et al., 2016; Yakoot et al., 2017), notably using day 2 (D2) viral load to determine treatment duration in genotype 1b infection. In this population, high cure rates were observed with just 3 weeks triple therapy (protease inhibitor [PI], NS5A inhibitor and NS5B inhibitor) (Lau et al., 2016). In a UK treatment shortening study, which used 4–8 weeks ombitasvir, paritaprevir, dasabuvir and ritonavir based on baseline viral load, all 10 individuals who became undetectable at D3 of treatment achieved first-line SVR12 regardless of treatment duration(Cooke and Pett, 2021). There is currently no data for RGT durations less than 8 weeks with SOF/DCV, which remains the lowest-priced and most widely available treatment option globally (Clinton Health Access Initiative, 2021). Drug resistance in association with particular viral genotypes and subtypes is also known to influence treatment outcome (Silva Filipe et al., 2017; Gupta et al., 2019) and may predict who can be treated with shortened therapy. Vietnam has a high burden of genotype 6 HCV infection (around 35%) (Irekeola et al., 2021), which is rare outside South East Asia and under-represented in clinical trials. Genotype 6 is the most genetically diverse HCV lineage (Hedskog et al., 2019), raising concerns about the potential for emergence of resistant variants (McPhee et al., 2019). The human IFNL4 di-nucleotide polymorphism rs368234815 (ΔG/TT) controls generation of the IFNL4 protein and is also associated with impaired clearance of HCV Prokunina-Olsson et al., 2013 and inferior responses to pegylated interferon-alpha/ribavirin therapy (Franco et al., 2014) and SOF-based treatment (Ansari et al., 2017; Ansari et al., 2019). The impact of host IFNL4 genotype in shortened DAA therapy is not well understood. It is also unknown how serum levels of SOF, its metabolite GS-331007, and DCV might impact treatment success with shortened therapy. In this prospective single-arm mechanistic study in HCMC, individuals with genotypes 1 and 6 HCV infection and mild liver disease were treated with shortened course SOF/DCV. We tested the hypothesis that high rates of cure can be achieved with short-course DAAs when early on-treatment virological response is used to guide duration of therapy. We also compared host IFNL4 genetic polymorphism, DAA drug levels, HCV subtypes and previously defined (in vitro) resistance-associated substitutions (RASs), in cures versus treatment failures to better understand the biological mechanisms determining treatment outcome. Methods Study population Participants were recruited from the outpatient hepatitis clinic of the Hospital for Tropical Diseases (HTD) in HCMC, between February 2019 and June 2020. Eligible patients were ≥18 years and had chronic infection with HCV genotype 1 or 6 without evidence of liver fibrosis (defined as a FibroScan score≤7.1 kPa, equivalent to F0-F1 disease) (Nitta et al., 2009). In addition, participants were required to be HCV-treatment naïve, have a BMI≥18 kg/m2, a creatinine clearance≥60 ml/min, with no evidence of HIV or Hepatitis B coinfection, or solid organ malignancy in the preceding 5 years. Full eligibility criteria are provided in the protocol available at https://doi.org/10.1186/ISRCTN17100273. Patients referred to the trial were initially enrolled into an observational study which included FibroScan assessment and genotyping. Individuals in this cohort found to be potentially eligible for the trial were invited for further screening. All patients provided written informed consent. Study design All participants were treated with sofosbuvir 400 mg and daclatasvir 60 mg (Pharco Pharmaceuticals, Egypt) administered orally as two separate tablets, once daily. Individuals requiring dose adjustment for any reason were excluded. Treatment duration was determined using hepatitis C viral load measured 2 days after treatment onset (D2). Participants with viral load <500 IU/ml at D2 (after two doses of SOF/DCV) were treated with 4-week SOF/DCV. Those with HCV RNA≥500 IU/ml received 8 weeks (Figure 1). The aforementioned study by Lau et al., 2016 reported 100% SVR12 following 3-week triple therapy using this threshold. We chose a minimum 4-week duration based on our broader inclusion criteria and the use of dual-class therapy. Figure 1 Download asset Open asset Study design. *HCV RNA on days 0, 1, 2, 7, 10, 14, 17, 21, 24, 28, (42, 56), EOT +3, EOT +7, EOT +10, EOT +14, EOT +17, EOT +21, EOT +24, EOT +28s, EOT +56, EOT +84. To determine viral kinetics on treatment (and on occasion of any failure), HCV viral load was measured at baseline (day 0) and at all subsequent follow-up visits on days 1, 2, 7 and then twice weekly until end-of-treatment (EOT) (Figure 1). Visits after EOT were scheduled twice weekly in the first month after completion of treatment, and then at 8 and 12 weeks after EOT. The primary endpoint was sustained virological response (SVR12) defined as plasma HCV RNA less than the lower limit of quantification (<LLOQ) 12 weeks after the EOT without prior failure. Failure of first-line treatment was carefully defined to incorporate individuals who fully suppressed HCV RNA (<LLOQ) on therapy with late virological rebound, as well as those who never fully suppressed HCV viral load. In both cases, two consecutive viral loads >LLOQ, taken at least 1 week apart, were required to confirm failure, with the second >2000 IU/ml. Once failure was confirmed, participants commenced retreatment with standard duration SOF/DCV within 2 weeks (Figure 1). Secondary endpoints were lack of initial virological response (<1 log10 decrease in HCV viral load from baseline), serious adverse events (SAEs), grade 3/4 clinical adverse events (AEs), AEs of any grade leading to change in treatment (SOF, DCV or any other concomitant medication) and adverse reactions (ARs). Severity of all AEs and ARs were graded using the Common Toxicity Criteria for Adverse Events gradings (National Institute of Health, 2017). Sample size justification We set a target cure rate of ≥90%, and an unacceptably low cure rate of 70%. Assuming 90% power and one-sided α=0.05, 37 participants were required to exclude the null hypothesis that cure was <90%. Assuming 5% loss to follow-up, and that, based on the study by Lau et al., 2016, 65% would suppress viral load <500 IU/ml by day 2 and receive 4 weeks (rather than 8 weeks) of therapy, the final target population was 60 participants, pooling genotypes 1 and 6. Study assessments At each visit, patients were assessed by a study doctor. AEs and ARs were recorded and graded according to a standardised scale (National Institute of Health, 2017) and medication adherence and use of healthcare facilities were recorded on case report forms. HCV RNA was measured in the hospital using the available commercial platform. At start of study (for the first 41 participants enrolled), this was the Abbott Architect (LLOQ=12 IU/ml). This was subsequently replaced with the COBAS AmpliPrep/COBAS TaqMan HCV Quantitative Test, version 2.0 (Roche Molecular Systems, LLOQ=15 IU/ml). Standard laboratory tests—including full blood count, renal function and liver function tests—were performed in the hospital laboratory at baseline, EOT and EOT+12. Virus sequencing At screening, HCV genotype and subtype were determined using NS5B, Core and 5′ UTR sequencing, according to the method described by Le Ngoc et al., 2019. To evaluate the impact of HCV subtypes and RASs on treatment outcome, whole-genome sequencing (WGS) was additionally performed on all enrolled participants’ virus at baseline, and upon virological rebound and at start of retreatment in participants failing therapy. WGS of the HCV viral genome was attained using Illumina MiSeq platform as described previously (Thomson et al., 2016; Smith et al., 2021b; Smith et al., 2021a; Manso et al., 2020). The de novo assembly’s nucleotide sequences were translated into amino acid and were aligned to H77 HCV reference (GenBank ID: NC_038882.1) and the NS5A and NS5B protein regions were extracted. We only looked for RAS that were present in at least 15% of the reads in the sample and had a read count of greater than 10. We used the Public Health England (PHE) HCV Resistance Group’s definition for RASs (Bradshaw et al., 2019). For genotype 1 we looked for RASs defined specifically for genotype 1 as they are well studied. For genotype 6 we looked for all RASs defined across all genotypes, as little work has been done on RASs in genotype 6. For DCV, we looked for 24R, 28T, 30E/K/T, 31M/V, 32L, 58D and 93C/H/N/R/S/W in genotype 1 infection and additionally looked for 28S, 30R and 31F in genotype 6 infection. For SOF, we looked for 159F, 237G, 282T, 315H/N and 321A/I in genotype 1 infection and additionally looked for 289I in genotype 6 infection (Ansari et al., 2017; Ansari et al., 2019). In addition to viral sequencing, we evaluated host genetic polymorphisms within the interferon lambda 4 (IFNL4) gene of all participants at baseline. Genotyping of IFNL4 rs368234815 was performed on host DNA using the TaqMan SNP genotyping assay and primers described previously (Prokunina-Olsson et al., 2013) with Type‐it Fast SNP Probe PCR Master Mix (Qiagen). Pharmacokinetics and pharmacodynamics To assess pharmacokinetics (PK) and pharmacodynamics (PD), the plasma drug levels of SOF, its inactive metabolite GS-331007, and DCV were measured at baseline, at day 14 and at EOT (day 28 or 56) in all participants. In addition, intensive drug level sampling was conducted in a subset of 40 participants, who were sequentially invited to join an ancillary PK study. In this subgroup, five samples were collected in each participant after the first dose of SOF/DCV and at day 28, according to one of two randomly assigned sampling schedules (A and B). In sampling schedule A, drug levels were measured at 0.5-, 2-, 4-, 6- and 24-hr post-dose; in sampling schedule B, drug levels were measured at 1-, 3-, 5-, 8- and 24-hr post-dose. Drug quantification was performed using liquid chromatography-tandem mass spectrometer at Mahidol Oxford Tropical Medicine Research Unit, Bangkok. Two separate analytical assays were developed and validated to quantify SOF plus its metabolite GS-331007, and DCV, respectively. Full methodological details of the PK/PD analysis are provided in Appendix 1. Statistical analysis Primary and secondary outcomes Analysis was performed under intention-to-treat (the per-protocol analysis, defined as including all participants taking 90–110% of prescribed treatment, was equivalent to the intention-to-treat analysis) with an additional post hoc analysis excluding those who were non-Gt1/6 from WGS. Where possible, proportions and 95% CIs were estimated from the marginal effects after logistic regression. Where no events were recorded and models would not converge, we used binomial exact 97.5% CIs. Absolute HCV VL was analysed using interval regression (incorporating censoring at the LLOQ) adjusting for baseline HCV VL. Differences between baseline means and medians in 4-week cures versus 4-week failures were analysed with unpaired t-tests and Wilcoxon rank-sum tests, respectively; differences in proportions were assessed using chi-squared tests or Fisher’s exact tests as appropriate. Analyses were performed using Stata v16.1 (StataCorp, 2019). Virus genomics Fisher’s exact test was used to test for association between presence and absence of each RAS and treatment outcome. To test for association between outcome and number of RAS, we used logistic regression. Pharmacokinetics and pharmacodynamics Intensive drug levels of SOF, its metabolite GS-331007, and DCV from the subset of 40 patients at days 0 and 28, together with any EOT samples at day 28, were analysed using non-compartmental analysis in PKanalix version 2020R1 (Lixoft, 2022). Two separate analyses were performed to characterise the pharmacokinetic properties of the study drugs. In the first, naïve pooled analyses were performed separately on data from days 0 and 28 (not including EOT samples) to derive median pharmacokinetic parameters at each day. In these analyses, the median concentration at each protocol time was calculated. Individual concentration measurements below the LLOQ were set to LLOQ/2 when calculating the median values. It was assumed that the participants had no drug concentrations at time 0. In the second analysis, data from days 0 and 28 were pooled for each individual. This resulted in a full pharmacokinetic profile for each subject, which was analysed with a non-compartmental approach. The mean value of drug concentrations was used if patients had two or more samples taken at the same time point. These derived individual drug exposures were used to evaluate the relationship between drug exposure and therapeutic outcome. It was assumed that the participants had no drug concentrations at time 0. In this analysis, the first measurement below LLOQ in a series of LLOQ samples was imputed as LLOQ/2 and the later measurements were ignored. In both approaches, SOF samples taken at ≥24 hr post-dose were excluded. SOF is a prodrug and has a very short half-life of less than 1 hr, which make concentrations at 24 hr after dose extremely unlikely (de Kanter et al., 2014). In addition, outcome variables and the relationship between outcome variables and drug exposure were evaluated. Additional detail of the PK/PD analysis is provided in Appendix 1. Ethical approval The trial was approved by the research ethics committees of The Hospital for Tropical Diseases (Hospital for Tropical Diseases Ethics Commitee, 2021) (ref: CS/BND/18/25), Vietnam Ministry of Health, 2022 (ref: 6172/QĐ-BYTtnam MoH), Imperial College London (Imperial College Research Ethics Committee, 2018) (ref: 17IC4238), and Oxford University Tropical Research Ethics Committee (Oxford Tropical Research Ethics Committee, 2018) (ref: 43-17). The study’s conduct and reporting is fully compliant with the World Medical Association’s Declaration of Helsinki on Ethical Principles for Medical Research Involving Human Subjects (World Medical Association, 2022). The trial was registered at ISRCTN, registration number is ISRCTN17100273 (ISRCTN registry, 2018). Results Baseline characteristics Of 455 patients screened, 52 were enrolled and 1 subsequently withdrew (Figure 2). Most exclusions were on account of either a FibroScan score of >7.1 kPa (with cirrhotic patients enrolled into a parallel study; Flower et al., 2021), or ineligible genotype. Figure 2 Download asset Open asset Screening and enrolment. 22/51 were initially identified as genotype 1 infection and 30 as genotype 6. With the benefit of WGS data, it was confirmed that 22 (43%) had genotype 1 infection, 27 (53%) had genotype 6, 1 had genotype 2 and another had genotype 4 infection. The latter two individuals were included in the intention-to-treat analysis but excluded from a post hoc analysis of G1 and G6 infections only. Recruitment was completed short of the initial target of 60 due to severe COVID-19-related restrictions in Vietnam from February 2020. These included clinic closures, travel restrictions and repurposing of the HTD as a COVID-19 treatment centre. Baseline and clinical characteristics are described in Table 1. One participant, a male with genotype 1b infection who was cured with 4-week therapy, had an HCV viral load of 618 IU/ml on day 0 which may have been consistent with spontaneously resolving acute infection, but could equally reflect fluctuating viraemia. Baseline viral load was >10,000 IU/ml in all other participants, who were all assumed to have chronic infection. Table 1 Baseline characteristics. N/ median%/rangeTotal participants52Age in years49.5(25.0, 67.0)Female29(56%)Body-mass index in kg/m223.3(18.7, 30.6)Genotype 122(43%)1a111b12 (1 withdrew)Genotype 627(53%)6a126e106h26l26u1Genotype 2(m)1Genotype 4(k)1Baseline HCV viral load in IU/ml1,932,775(618, 11,200,000)HCV viral load – log10 IU/ml (range)6.3(2.8, 7.0)Past medical history:Illicit drug use4(8%)Alcohol dependence (historic; current excluded)4(8%)Diabetes2(4%)Hypertension7(13%)Ischaemic heart disease1(2%)Tuberculosis2(4%)Current smoker18(35%)Previous spontaneous clearance of HCV with re-infection2(4%) Treatment duration, adherence and efficacy outcomes By day 2, 34 participants (65%) had HCV viral load below the threshold of 500 IU/ml (Figure 2; Table 2), so received 4-week treatment. Eighteen participants were above the threshold at this time point, of which 1 withdrew after 9 days of treatment, meaning 17 completed 8-week therapy. Adherence was good, with 96% completing the full prescribed course of SOF/DCV (as assessed by self-reporting and physician pill count). Eighteen (35%) participants missed at least one visit because of COVID-19-related restrictions. Of the 51 participants with outcome data, 38 (75% [95% CI (63, 86)]) achieved SVR12 while 13 failed therapy and required retreatment. All treatment failures occurred in individuals who received 4-week therapy, translating to an SVR12 of 62% (21/34; 95% CI (44, 78)) in rapid responders who received 4-week therapy, and 100% (17/17; 97.5% CI (80, 100)) in slower responders who received 8-week SOF/DCV (Figure 3; Table 2). Figure 3 Download asset Open asset Primary outcome, with HCV subtypes (n=51). All 13 individuals who experience treatment failure with 4-week SOF/DCV were cured with 12-week SOF/DCV retreatment. Table 2 Treatment outcome. N/median%/rangeDetectable HCV viral load (HCV VL) at day 25096% Abbott39/4195% COBAS11/11100%Median (IQR) HCV VL at day 2 in IU/ml269(104, 690) Abbott217(101, 690) COBAS459(209, 832)Below threshold—for 4-week therapy34(65%) Abbott31(66%) COBAS3(60%)Above threshold—for 8-week therapy18(35%) Abbott16(34%) COBAS2(40%)Mean (SD) duration of first-line therapy received in days37(13.7)Mean (SD) duration of all therapy received in days58(34.2)Median weeks from enrolment to last visit (range)20(1, 42)Primary outcomeOutcome available51SVR12 by intention-to-treat analysis and per protocol analysis38(75% [95% CI 63, 86])SVR12 by sensitivity analysis (i) [missing results = failure]38(73% [95% CI 61, 85])SVR12 by post hoc analysis (ii) [G1 and G6 only]37(76% [95% CI 63, 88])Secondary endpointsLack of initial virological response0(0% [97.5% CI 0, 7])Serious adverse events0(0% [97.5% CI 0, 7])Grade 3/4 clinical adverse events0(0% [97.5% CI 0, 7])Non-serious adverse reactions18(35% [95% CI 22, 48])Adverse events or reactions leading to change in study medication0(0% [97.5% CI 0, 7]) Where not labelled, data presented as n (%; 97.5% confidence interval). Of the 13 participants who underwent retreatment, 100% were cured. The mean first-line SOF/DCV treatment duration was 37 days (standard deviation, SD 13.7), with a first-line cure rate of 75%. The mean (SD) total SOF/DCV duration (i.e., including 12-week retreatment where required), was 58 (34.2) days per patient, with a 100% cure rate. There was no evidence of differences in age, gender, BMI, IFNL4 genotype, transaminases or baseline HCV viral load between patients who achieved cure with 4-week treatment versus those who experienced treatment failure with 4-week treatment (Table 3). Table 3 Comparison of baseline factors, drugs levels and virological response in individuals failed to achieve SVR12 with 4-week therapy versus those who cured with 4- or 8-week therapy. 4-week cures (n=21)4-week failures (n=13)p8-week cures (n=17)Host factorsMale (%)62%38%0.1829%Mean age45480.2355Mean BMI23230.4024Median ALT54360.1031Median AST34280.4433IFNL4 delG/TT and TT/TT genotypes (rs368234815)71%58%0.4769%Virus factorsMedian D0 HCV VL916,0002,139,2580.204,982,889 Abbott960,9131,972,8410.474,625,118 COBAS916,0005,260,0000.404,605,000D2 VL<LLOQ2/21 (10%)0/13 (0%)0.510% Abbott2/18 (11%)0/10 (0%)0.410/13 (0%) COBAS0/3 (0%)0/3 (0%)–0/5 (0%)D7 VL<LLOQ9/21 (43%)1/12 (8%)*0.0540% Abbott8/18 (44%)1/9 (11%)0.090/13 (0%) COBAS1/3 (33%)0/3 (0%)1.000/5 (0%)D10 VL<LLOQ9/21 (43%)9/13 (69%)0.176% Abbott8/17 (47%)8/10 (80%)0.121/10 (10%) COBAS1/4 (25%)1/3 (33%)1.000/6 (0%)D14 VL<LLOQ14/21 (68%)9/13 (69%)1.0018% Abbott11/16 (69%)6/9 (67%)1.001/11 (18%) COBAS2/4 (50%)3/4 (75%)1.001/6 (17%)HCV genotype 110/21 (48%)6/13 (46%)1.00(vs Gt 6)6/17 (35%)1a4/21 (19%)5/13 (38%)0.15(vs 1b)2/17 (12%)1b6/21 (24%)1/13 (8%)4/17 (24%)HCV genotype 610/21 (48%)6/13 (46%)11/17 (65%)6a6/21 (29%)2/13 (15%)0.58(vs. 6e)4/17 (24%)6e†3/21 (14%)3/13 (23%)4/17 (24%)Resistance-associated substitutionsMedian (range) SOF-RAS0 (0–1)0 (0–2)0.760 (0–1)Median (range) DCV-RAS2 (0–2)1 (0–2)0.172 (0–4)Median (range) SOF- & DCV-RAS combined2 (0–3)2 (1–2)0.122 (0–4)Drug exposure