As pandemic influenza H1N1 unfold all over the world in 2009, illness severity was one of many most important areas of curiosity. The case fatality ratio (CFR) is a consultant measurement of severity of a illness that straight captures virulence (ie, the conditional threat of loss of life for sufferers with a illness or an infection), whereas mortality (ie, the danger of loss of life in a inhabitants) relies upon not solely on the illness severity but in addition the danger of an infection in a inhabitants. As a result of there have been a number of conflicting estimates of the CFR for pandemic H1N1,1, 2, 3, 4, 5, 6 I provide an interpretation of those stories and determine key areas that should be clarified.