Harvard Expert Estimates Very Low Mortality Rate for 2009 H1N1 Pandemic

A Harvard epidemiologist, Marc Lipsitch, estimates the mortality rate for disease due to the 2009 H1N1 virus at 0.007%-0.045%, according to Reuters. This estimate is at least an order of magnitude lower than the US mortality rate calculated by using CDC case, hospitalization, and death data (~0.75%*) and even lower than the crude mortality rate according to WHO data (>1%).

Lipsitch proposes that the mortality risk due to the 2009 H1N1 virus is comparable to that of a "moderate" influenza season—less than 0.1%.** The epidemiologist bases his calculation on reports of influenza-like illness throughout the world, as well as reports of hospitalizations and confirmed deaths.

Working backward, one can conclude that Lipsitch estimates the number of people infected so far with the 2009 H1N1 virus worldwide at several million.

* Calculated by multiplying the US hospitalization ratio from April 15 to July 24, or 0.114, by a recent in-hospital death ratio (eg, 0.065) and then multiplying by 100.

** Although CDC data suggest a death rate for seasonal flu that is higher than 0.045%. According to the Centers, 5%-20% of the US population is affected each year by seasonal influenza. The US population is approximately 300 million, so that means 15-60 million are infected annually. About 36,000 people die of seasonal flu, for an annual mortality rate of 0.06%-0.24%. About 200,000 are hospitalized, for a hospitalization rate of 0.3%-1.3%.

Depiction of H1N1 virus from Wikipedia.