Why was the 2009 pandemic so mild?

Abstract

The WHO declared the first pandemic of the 21^st century in June 2009 [influenza A(H1N1)pdm09]. The exact burden of the pandemic is still unknown and data continues to emerge on the direct and indirect costs associated with this pandemic. In this review we explore why the 2009 pandemic was so mild, what we might have done better to control and manage it then suggest some lessons for the future.

Compared to previous influenza pandemics, the 2009 pandemic would be considered mild. It raises questions as to whether the pandemic virus was less virulent compared with previous pandemics and/or whether advances in modern medicine helped to keep the mortality low. This is the first pandemic that has been tackled with the combination of antivirals, antibiotics, vaccines for both the virus and bacterial super-infections as well as advanced intensive-care management.

The pandemic influenza virus showed some remarkable antigenic and genetic similarities with the 1918 pandemic H1N1 virus. Related to this, it spared the elderly who are usually at much higher risk of influenza morbidity and mortality during seasonal epidemics and pandemics.

Keywords

Influenza - pandemic - mild