Abstract: Vitamin A in resistance to and recovery from infection: relevance to SARS-CoV2 C. B. Stephensen1* and G. Lietz2* 1 Immunity and Disease Prevention Research Unit, USDA Western Human Nutrition Research Center, and Nutrition Department, University of California, Davis, CA, USA 2 Human Nutrition Research Centre, Population Health Sciences Institute, Newcastle University, Newcastle upon Tyne NE2 4HH, UK (Submitted 12 September 2020 – Final revision received 30 December 2020 – Accepted 13 January 2021) Abstract SARS-CoV2 infects respiratory epithelial cells via its cellular receptor angiotensin-converting enzyme 2, causing a viral pneumonia with pronounced inflammation resulting in significant damage to the lungs and other organ systems, including the kidneys, though symptoms and disease severity are quite variable depending on the intensity of exposure and presence of underlying conditions that may affect the immune response. The resulting disease, coronavirus disease 2019 (COVID-19), can cause multi-organ system dysfunction in patients requiring hospitalisation and intensive care treatment. Serious infections like COVID-19 often negatively affect nutritional status, and the resulting nutritional deficiencies may increase disease severity and impair recovery. One example is the viral infection measles, where associated vitamin A (VA) deficiency increases disease severity and appropriately timed supplementation during recovery reduces mortality and hastens recovery. VA may play a similar role in COVID-19. First, VA is important in maintaining innate and adaptive immunity to promote clearance of a primary infection as well as minimise risks from secondary infections. Second, VA plays a unique role in the respiratory tract, minimising damaging inflammation, supporting repair of respiratory epithelium and preventing fibrosis. Third, VA deficiency may develop during COVID-19 due to specific effects on lung and liver stores caused by inflammation and impaired kidney function, suggesting that supplements may be needed to restore adequate status. Fourth, VA supplementation may counteract adverse effects of SARS-CoV2 on the angiotensin system as well as minimises adverse effects of some COVID-19 therapies. Evaluating interactions of SARS-CoV2 infection with VA metabolism may thus provide improved COVID-19 therapy. Key words: SARS-CoV2: COVID-19: Vitamin A: Retinoic acid: Immunity: Angiotensin-converting enzyme 2 (ACE2): Lipofibroblasts The Coronaviridae family of single-stranded RNA viruses includes four genera: alpha-, beta-, gamma- and deltacoronavirus(1). Seven coronaviruses are known to infect humans. Two (229E and NL63) from the alpha genus and two (OC43 and HKU-1) from the beta genus cause mild upper respiratory tract infections and symptoms of the common cold. The remaining three human coronaviruses are also in the beta genus but cause severe lower respiratory tract infections, respiratory failure and death. These viruses are MERSCoV, which causes the Middle East respiratory syndrome; SARS-CoV1, which causes severe acute respiratory syndrome, and SARS-CoV2, which is causing the current pandemic of coronavirus disease 2019 (COVID-19) (1,2). SARS-CoV2 spreads readily from person-to-person due to the long incubation period of 2–14 d following infection(3) and, according to data available to the WHO, has infected 75 million people and caused 1·7 million deaths worldwide between December 2019 and December 2020(4). SARS-CoV2 infection causes..