There were 18,500 lab-confirmed deaths from the the 2009 pandemic influenza A H1N1 that were reported to the World Health Organization (WHO). This obviously did not include every person who died from H1N1 and it was likely only a small percentage of the actual deaths caused by the pandemic. A report
in The Lancet Infectious Diseases
estimated that deaths may have been 15 to 30 times this amount.
The researchers estimate that globally there were 151,700 to 575,500 deaths from H1N1. The estimate includes an average of 201,200 respiratory deaths, with a range estimate of 105,700 to 395,600. It also includes an additional average estimate of 83,300 cardiovascular deaths, with a range of 46,000 to 179,900.
The researchers also say 80% of the respiratory and cardiovascular deaths were in people younger than 65 years and 59% occurred in southeast Asia and Africa.
Here are the methods the researchers used to come up with the estimates:
We calculated crude respiratory mortality rates associated with the 2009 pandemic influenza A H1N1 strain by age (0—17 years, 18—64 years, and >64 years) using the cumulative (12 months) virus-associated symptomatic attack rates from 12 countries and symptomatic case fatality ratios (sCFR) from five high-income countries. To adjust crude mortality rates for differences between countries in risk of death from influenza, we developed a respiratory mortality multiplier equal to the ratio of the median lower respiratory tract infection mortality rate in each WHO region mortality stratum to the median in countries with very low mortality. We calculated cardiovascular disease mortality rates associated with 2009 pandemic influenza A H1N1 infection with the ratio of excess deaths from cardiovascular and respiratory diseases during the pandemic in five countries and multiplied these values by the crude respiratory disease mortality rate associated with the virus. Respiratory and cardiovascular mortality rates associated with 2009 pandemic influenza A H1N1 were multiplied by age to calculate the number of associated deaths.