Covid-19 is a global pandemic causing unprecedented morbidity and mortality in thegeneral population. It appears to have a greater effect on the elderly or those withunderlying health problems but is not exclusively confined to these groups. As peopleage, particularly toward the end of their lives, the response of the immune system beginsto drop away, an occurrence known as immunosenescence. It is known that there exist agroup of people that do not respond to immune stimulation in a normal way but who may toobservers be considered fit and healthy. The leukocyte immune test (LIT) relies upon thesupramaximal stimulation of white cells outside of the body to determine theirreactiveness when stimulated. It is intended to study patients admitted to Barts Healthwith diagnosed Covid-19. 4 ml blood will be taken of which 10microlitres will be used forthe LIT. The remainder will be used for measurement of antibody levels previouslyassociated with poor outcome following cardiac surgery. The patients will be followed upto see the proportion that progress to requirement for critical care, advancedventilatory support, renal failure and in-hospital mortality. If a link can beestablished between a poor outcome following admission to hospital with Covid-19 and theimmune response on admission, as predicted by means of the LIT, then it may enable betterformulation of potential treatment strategies. Being able to measure at point ofadmission the responsiveness of someone's immune system may mean that treatmentstrategies such as the administration of passive immunization either via convalescentplasma or gammaglobulin will be better guided. If the LIT proves able to identify thosepeople at risk of severe disease it may be able to identify individuals amongsthealthcare workers that may benefit from passive immunisation or avoidance of high-riskexposure to Covid-19.