WHO - Assessing Severity of an Influenza Pandemic

"The major determinant of the severity of an influenza pandemic, as measured by the number of cases of severe illness and deaths it causes, is the inherent virulence of the virus. However, many other factors influence the overall severity of a pandemic’s impact.

Even a pandemic virus that initially causes mild symptoms in otherwise healthy people can be disruptive, especially under the conditions of today’s highly mobile and closely interdependent societies. Moreover, the same virus that causes mild illness in one country can result in much higher morbidity and mortality in another. In addition, the inherent virulence of the virus can change over time as the pandemic goes through subsequent waves of national and international spread. "

WHO considered the following factors before characterizing the severity of the current pandemic influenza as "moderate":

• properties of the virus;
• population vulnerability;
• subsequent waves of spread;
• capacity to respond; and
• an assessment of the current situation

Detailed information and a breakdown of these factors can be viewed on WHO's website: http://www.who.int/csr/disease/swineflu/assess/disease_swineflu_assess_20090511/en/index.html


Additionally, this week's WHO Weekly Epidemiological Record is entitled Considerations for Assessing the Severity of an Influenza Pandemic. The information in this document is presented in both English and French. http://www.who.int/entity/wer/2009/wer8422.pdf