## 4 Discussion
For leadership, our rapid response team enabled immediate, confident, and transparent communication between staff; for education, periodic updates of informative posters and regular broadcasting to both the medical team and patients were performed in our HD unit every day; for preparedness and proactive management, a series of strategies focusing on space segmentation, access control, quarantine operations, and high-quality medical staff protection were built to optimize prevention control; ultimately, for the recovery stage, we stepped down our preventive plans, guided by using serial assessments of Rt values and regional prevalence rates, to restore the healthcare capacity and resource utilization into normal medical functioning. The COVID-19 vaccination program was very effective and has helped to achieve an inoculation rate of 82% to mid-July in our HD units. The application of all these policies was possible to contain COVID-19 transmission in our HD unit maintaining zero cases of infection to this day since the initiation of community outbreak in Taiwan. The high mortality rate (66.6%) in COVID-19-infected HD patients in Keelung was peculiar. Analyses of the outcomes of COVID-19 infection have revealed overall mortality of 22.4% (ranged from 8.9 to 43.9%) in various HD patient cohorts reported in 2020 [10]. Common prognostic factors for mortality in COVID-19-infected HD patients included greater age, male gender, underlying comorbidities (cardiac or pulmonary disease, diabetes, and hypertension), and the use of mechanical ventilation, corticosteroids, or wheelchairs [36; 38; 39]. In addition to all these factors, the increased chest-thoracic ratio was also a poor prognostic predictor among our HD patients, highlighting the importance of fluid control and underlying cardiac performance in improving outcomes. Furthermore, the mortality of the second wave of the outbreak affected by COVID variants was higher than the initial global pandemic [40]. HD patients infected with SARS-CoV-2 variants B.1.362 (from Israel) were more likely to have critical COVID-19 (defined as a condition associated with organ failure requiring ventilation or hemodynamic support), shorter survival time, and poorer outcome, having a mortality rate as high as 57% than the non-variants COVID-19-infected HD patients [40]. Information regarding the outcome of HD patients infected with the SARS-CoV-2 variant B.1.1.7 (from the UK), the main virus strain in Taiwan, remains scarce. Large populational cohort studies revealed that patients infected with variants B.1.1.7 had a greater hospitalization rate, higher risk for intensive care, and higher 28-day mortality compared with patients with non-B.1.1.7 SARS-CoV-2 [41; 42]. The emergency of SARS-CoV-2 variants has again emphasized the importance of infection control in HD settings because of the increased infectivity, virulence, and adverse outcome associated with these virus stains. The HD unit of Chang Gung Memorial Hospital at Keelung is the largest renal care center in the region. We have successfully contained the COVID-19 infection and no secondary transmission was noted, despite the presence of one confirmed HD case infected from the household. National universal measures were rapidly implemented in addition to our specific preventive strategies from the beginning of the outbreak. Although we have provided a successful care model in preventing COVID-19 transmission in an HD facility, several works should be further addressed. First, many of our specific preventive plans were both resource- and time-consuming and may not be applicable to other private HD settings or areas of low prevalence rates. Our HD unit is a hospital-affiliated setting caring for approximately 500 HD patients, in which multidisciplinary infrastructure and medical resources are adequate to support all of the measures.