Why can COVID-19 fatality in space be significantly higher than on Earth?

Astronauts are exposed to a wide variety of stressors ranging from radiationand microgravity to persistent fluids shifts, circadian shifts and thepsychological stress of prolonged isolation and confinement. on deep spacemissions, beyond the range of the earth's magnetosphere, ionizing radiationmay increase oxidative stress and dna damage, immune systemdysregulation and alter the effectiveness of the cellular defense mechanisms.by reviewing the health problems reported by astronauts participated inprevious space missions, it is evident that viral infections are not rare inspace. recent reports suggest that covid-19 can last for a long time incommunities. although nasa implements countermeasures designed to limitcrew illness during space missions such as a pre-flight quarantine, it is notclear whether an outbreak can be prevented. currently, it is not likely thatastronauts could get a viral infection, but the consequences of potential lifethreateningviral diseases such as covid-19 should be better characterized. inthis paper we discuss why covid-19 fatality in space might be significantlyhigher than on the earth. the reasons for such an increased risk include 1)uselessness of social distancing due to microgravity 2) immune systemdysregulation 3) possibly higher mutation rates of rna viruses such as thenovel coronavirus (sars-cov-2) 4) existence of strong selective pressure and5) decreased maximum oxygen uptake. given these considerations, thecombined effects of microgravity, space radiation (and possibly other majorspace stressors) on the immune system of astronauts exposed to sars-cov-2and possible interactions of the virus, space stressors and host should becarefully investigated.