Select a language:

Pandemic Influenza


CDC Pandemic Intervals Framework, 

An influenza pandemic is a global outbreak of a novel influenza A virus that emerges and is able to infect people easily and spread from person to person in an efficient and sustained way.  Since these viruses are new, people generally do not have immunity to them and vaccine is not readily available, so infection rates, morbidity and mortality can be high.    The last influenza pandemic was in 2009 when influenza A (H1N1)pdm09 emerged and spread rapidly across the United States and world.  Between April 2009 and April 2010, the Centers for Disease Control and Prevention (CDC) estimated there were approximately 60.8 million cases, 274,304 hospitalizations and 12,469 deaths in the U.S. due to influenza A (H1N1)pdm09.  See for more information.

An influenza pandemic can emerge anywhere and spread globally.  During a pandemic, hospitals and healthcare may be overwhelmed and schools and businesses may close.  As part of efforts to lessen (mitigate) the effects of the pandemic on the community, non-pharmaceutical interventions (NPIs) may be recommended.  For more information, see Community Mitigation Guidelines to Prevent Pandemic Influenza, United States, 2017.

The CDC and World Health Organization (WHO) monitor for novel viruses which are emerging and evaluate their potential pandemic risk.  See Summary of Influenza Risk Assessment.

Last reviewed January 14, 2019