2.1. Study design
The study was part of our previous retrospective study of Covid-19 patients in Yogyakarta and Central Java provinces, Indonesia.36 Briefly, the study was conducted from May 2021 to February 2022. We collected nasopharyngeal swabs of outpatient or hospitalized patients with Covid-19 for RT-PCR testing in the Laboratory of Covid-19, Faculty of Medicine, Public Health and Nursing, Universitas Gadjah Mada, Yogyakarta. During the study period, 352 confirmed Covid-19 patients (based on RT-PCR), consisting of 164 males and 188 females, were recruited.