Comparing vitamin D receptor gene polymorphisms in rs11568820, rs7970314, rs4334089 between COVID-19 patients with mild and severe symptoms: a case control study oleh Noushin Mohammadifard, Ladan Sadeghian, Razieh Hassannejad, Elham Khosravi, Mojgan Gharipour, Simin Karimi, Shidokht Hosseini, Mahtab Sepahifar, Ghazaleh Bahrami, Fahimeh Haghighatdoost, Nizal Sarrafzadegan