“…Moreover, the range of factors examined by these retrospective or cross-sectional studies was rather limited. Factors significantly or non-significantly associated with Covid-19 were sex 1 , age 1 , ethnicity 2 , urbanisation 3 , residence in a multifamily unit 4 , BMI and obesity 2,5,6 , smoking 2,7 , physical fitness and forced expiratory volume 2 , the number of daily contacts 3 , wearing masks and washing hands 3 , socioeconomic deprivation 2 , particular AB0 blood groups [8-10], Rh factor [10], vitamin D deficiency [11], high-density lipoprotein level 2 , use of immunosuppressants 8 , and a growing set of comorbidities – cardiovascular disease, chronic obstructive pulmonary disease (COPD), chronic kidney disease, dementia, hypertension and functional dependence 6 , and toxoplasmosis 9 . Other factors, such as contact with animals, have been suggested only on a theoretical basis 10 or are merely discussed in non-scientific sources, such as popular literature or the internet.…”