Covid's natural born victims
![Covid's natural born victims](http://cellgs.e2ecdn.co.uk/ArticleImages/severe-covid1.jpg?w=755&h=500&mode=pad&quality=85)
Why do some people fall seriously ill and die with Covid whilst others are asymptomatic? A remarkable characteristic of Covid-19 is the way it affects individuals so differently: Around 40% of people infected with SARS-CoV-2 are asymptomatic. A further 40% experience mild, upper respiratory tract symptoms. The remaining 20% develop pneumonia, of which 10% will become hypoxic, leading to critical illness in around 3%. In addition to age, sex and underlying health issues, the ability to deploy key immunomodulatory cytokines has emerged as an important risk factor for mortality.