**4. Discussion**

Our study revealed a 100% efficacy and a suitable safety profile of LDV/SOF treatment in children aged 12 to 17 years infected with genotypes 1 and 4 HCV. This therapy has been approved by the FDA and EMA for use in children aged 3 years and older with CHC based on the results of three open-label single-arm clinical trials [8–10]. However, one of the biggest problems of clinical trials is selection bias, which may lead to a mismatch between the trial population and real-world patients. Thus, their results should be confirmed by real-life studies, which would also include specific subgroups of patients, e.g., with liver cirrhosis, HIV/HCV, or HIV/HBV coinfections. In a recently published systematic review with meta-analysis on the efficacy and safety of different DAAs (including LDV/SOF) in children and adolescents with CHC, Indolfi et al. [13] demonstrated that among 39 included studies (both clinical trials and real-life studies) on 1796 subjects, the pooled SVR12 proportion among patients receiving all doses of the therapy was 100% (95% confidence interval 100–100). Among patients who received at least one dose of DAA, the lowest efficacy of the treatment (83%) was reported for children with cirrhosis [13]. However, it should be emphasized that the number of performed studies on LDV/SOF treatment in children and adolescents remains limited, and there is a need for further research in this area. We identified 15 papers (both clinical trials and real-life studies) that analyzed SVR in almost 1000 pediatric patients treated with LDV/SOF (Table 4). In all of these investigations, the treatment was effective in at least 95% of patients, which is consistent with our results, showing SVR in 97% of participants. The few patients who did not achieve SVR were (as in our study) lost to follow-up. There were only single cases described of relapse after the treatment [9]. Pooled data from the 15 abovementioned studies and our investigation on 1016 patients revealed an SVR rate of 98.6% for all genotypes, including 98.4% for patients infected with genotype 1, 75% for genotype 3, and 98.9% for genotype 4 HCV (Table 4). Lower SVR rates for genotype 3 may result from a small number of patients in this group (only 4). It is worth emphasizing that real-life studies on LDV/SOF treatment in children were mainly performed in Egypt; thus, they mainly investigated patients infected with genotype 4 HCV [17–23]. Studies analyzing the efficacy of LDV/SOF in children infected with genotype 1 are less represented. In a recently published Italian study by Serranti et al. [24], 78 patients were included: 64 infected with genotype 1; 2 with genotype 3; and 12 with genotype 4 HCV. The overall intention-to-treat SVR12 rate was 97.4%, but per-protocol analysis revealed SVR12 rates of 100% overall and separately for all genotypes (1, 3, and 4 HCV). This observation was similar to our results: our per-protocol SVR12 rates were 100% irrespective of the HCV genotype, duration of the treatment, previous treatment experience, or baseline extent of liver fibrosis (Table 2). It is worth emphasizing that the treatment was effective in cirrhotic patients and in two participants coinfected with HIV, as described in detail in another paper [25]. In addition, one of our patients had evidence of past HBV infection with detectable anti-HBc total antibodies. He was closely monitored during and after the treatment, and reactivation of the HBV infection did not occur (ALT and AST levels were normal, HBV DNA was undetectable during and after the treatment) [26]. In a large cohort of adults with HCV/HBV coinfection treated with DAAs, the risk of HBV reactivation in HBsAg-negative/anti-HBc-positive patients was only 0.16% [26]. To avoid HBV reactivation in patients with serologic evidence of a previous or current HBV infection, the clinical and laboratory signs of a hepatitis flare or HBV reactivation should be monitored during treatment with DAAs and posttreatment

follow-up. Despite the fact that elevation of the ALT and AST serum levels in patients with CHC is not obligatory and usually not persistent, we found a significant decrease in their levels during the course and after the treatment, which is consistent with observations of the Italian cohort [24].


**Table 4.** Summary of the studies on LDV/SOF efficacy in pediatric patients with chronic hepatitis C.

\* cumulative data from studies No. 1–4 and 6–15 and from our study (participants of study No. 5 are included in study No. 6); \*\* cumulative data from the above studies No. 3, 6, 12, 15 and from our study; \*\*\* cumulative data from the above studies No. 6 and 12; \*\*\*\* cumulative data from the above studies No. 1, 4, 6–15 and from our study, SVR—sustained virological response.

> The treatment with LDV/SOF was well tolerated. No participant discontinued the treatment due to side effects. However, a number of patients complained of the large size of the tablets, which were difficult to swallow. No patient complained of the taste of the drug, which was reported in the cohort of younger children (receiving pellets) [10]. According to the results of the meta-analysis performed by Indolfi et al. the most common adverse events reported in children and adolescents receiving DAAs include headache (19.9%), fatigue/asthenia (13.9%), nausea (8.1%), abdominal pain (7.0%), diarrhea (4.8%), cough (4.0%), and vomiting (2.6%) [13]. Similar side effects were observed in our cohort, with fatigue as the most common (14%). No serious adverse events were reported in the meta-analysis or in our study [13].

> Teenagers constitute a special group of pediatric patients; they usually have a sense of immortality, they want to be independent, and their adherence to longer-lasting therapies and obligatory checkups is usually poor. Thus, the value of the study is the fact that it was possible to carry out the entire therapy program and follow-up in 36/37 patients. This indicates that treatment based on DAAs is short and well tolerated by this specific age group of patients.

> The treatment duration in our study was established according to the ESPGHAN guidelines, with a minimum duration of 12 weeks [15]. However, there is some evidence based on four reported studies (Table 4) that shortening the duration of LDV/SOF treatment to 8 weeks is equally effective [17,20,24,27]. In the studies by Serranti et al. [24,28], 17 patients in total who were infected with genotype 1 HCV, treatment-naïve, noncirrhotic, and with baseline HCV viral load below 6,000,000 IU/mL were treated with LDF/SOF for 8 weeks. The SVR12 rate in this group was 17/17 (100%). Our data showing that most

of the patients had undetectable HCV RNA at 4 weeks of treatment may, to some extent, support shortening LDF/SOF treatment in adolescents.

Our study has some limitations. First, the number of included patients was relatively low. Our study group represents no more than 10% of all pediatric HCV cases diagnosed in Poland during the last decade (2). However, all consecutive patients infected with genotypes 1 and 4 HCV referring to our department were included. To the best of our knowledge, this is the second report on a real-life experience with LDV/SOF in adolescents from Europe, demonstrating the efficacy in participants infected with genotype 1 HCV. As presented in Table 4, studies on the large groups of pediatric patients in this area are unavailable. In addition, our 32 patients infected with genotype 1 HCV represented 10% of all of the pediatric study participants with genotype 1 treated with LDV/SOF (Table 4). Second, gaps in the available data resulting from the disruption caused by the COVID-19 pandemic should be mentioned. However, treatment was completed by all of the patients despite the pandemic, which was achieved thanks to the several efforts that were made to prioritize patient care in our children with CHC, following our own guidelines in this field [31]. In addition, DAA therapies are relatively simple, short, and safe. Thus, less frequent monitoring of patients receiving them might be considered.

In conclusion, the results of this real-life study confirm previous observations based mainly on clinical trials of a suitable efficacy and safety profile of LDV/SOF for the treatment of CHC genotypes 1 and 4 in adolescents, regardless of baseline liver fibrosis or previous ineffective antiviral treatment experience.

**Author Contributions:** Conceptualization, M.P.-S.; methodology, M.P.- ´ S.; formal analysis, M.P.- ´ S.; ´ investigation, M.P.-S., A.D., and M.A.; data curation, M.P.- ´ S., A.D. and M.A.; writing—original draft ´ preparation, M.P.-S.; writing—review and editing, M.P.- ´ S.; visualization, M.P.- ´ S.; supervision, M.M. ´ All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding. The therapeutic program was available courtesy of the donation of LDV/SOF by the pharmaceutical company (Gilead Sciences Poland Sp. Z o. o., Warsaw, Poland). The pharmaceutical company did not have any role in performing the study, nor in writing or approving this manuscript.

**Institutional Review Board Statement:** The investigation was performed in accordance with the ethical standards in the 1964 Declaration of Helsinki and its later amendments. The local ethics committee of the Medical University of Warsaw approved this study (No KB/87/2019; date of approval: 13 May 2019).

**Informed Consent Statement:** Written informed consent was collected from all the patients and/or their parents/guardians before their inclusion in the study.

**Data Availability Statement:** The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

**Acknowledgments:** The authors would like to thank the following clinicians for referring their patients for participation in the POLAC Project: Anna Gorczyca, Maria Rokitka, Ewelina Gowin, Joanna Łasecka-Zadrozna, J ˙ ózef Rudnicki, Mariola Purzy ´nska, Agnieszka Ogrodnik, Anna Mania, Magdalena Figlerowicz, Barbara Hasiec, Agnieszka Krasiukianis, and Ewa Majda-Stanisławska.

**Conflicts of Interest:** The authors declare no conflict of interest.
