In a paper titled "Human infection with avian influenza A H7N9 virus: an assessment of clinical severity" published in the Lancet, the authors have concluded that the fatality risk for patients that enter a hospital after having contracted the H7N9 avian flu virus at 36%.
The authors obtained information about laboratory-confirmed cases of avian influenza A H7N9 virus infection reported as of May 28, 2013, from an integrated database built by the Chinese Center for Disease Control and Prevention. They estimated the risk of fatality, mechanical ventilation, and admission to the intensive care unit for patients who required hospital admission for medical reasons. They also used information about laboratory-confirmed cases detected through sentinel influenza-like illness surveillance to estimate the symptomatic case fatality risk.
Based on the mortality rate of 36%, human infections with avian influenza A H7N9 virus seem to be less serious than has been previously reported. Many mild cases might already have occurred. Continued vigilance and sustained intensive control efforts are needed to minimise the risk of human infection.
While somewhat more benign than the previous strain identified in 2003, we are still seeing the emergence of difficult to transmit, but highly lethal strains from time to time. We still believe it only to be a question of time until a specific strain becomes more virulent.