HHS Pandemic Planning Scenarios

This graph displays the HHS Pandemic Planning Scenarios based on the Pandemic Severity Assessment Framework. The Pandemic Severity Assessment Framework uses a combined measure of clinical severity and transmissibility to characterize influenza pandemic scenarios. The horizontal axis is the scaled measure of clinical severity, ranging from 1 to 7, where 1 is low, 4 is moderate, and 7 is very severe. The vertical axis is the scaled measure of transmissibility, ranging from 1 to 5, where 1 is low, 3 is moderate, and 5 is highly transmissible. On the graph, HHS pandemic planning scenarios are labeled across four quadrants (A, B, C and D). From left to right, the scenarios are “seasonal range,” “moderate pandemic,” “severe pandemic” and “very severe pandemic.” As clinical severity increases along the horizontal axis, or as transmissibility increases along the vertical axis, the severity of the pandemic planning scenario also increases.

Quadrant A is located in the lower left hand corner and the corresponding HHS pandemic planning scenario is the “seasonal range.” Within this quadrant, influenza activity is characterized by low clinical severity (1 to 4 range) and low transmissibility (1 to 3 range). The 2011-2012 and the 2014-2015 influenza seasons are plotted as examples of past flu seasons that fall within this range.

Quadrant B is located in the upper left hand corner and the corresponding HHS pandemic planning scenarios are “seasonal range” and “moderate pandemic.” In quadrant B, influenza activity is characterized by low clinical severity (1 to 4 range) and moderate to high transmissibility (3 to 5 range). The 2009 pandemic is plotted on the graph as “seasonal range,” with clinical severity at 2 and the transmissibility at 3. The 1968 pandemic is plotted on the graph as a “moderate pandemic,” with clinical severity at 3 and a transmissibility at 4. The 1957 pandemic is also plotted on the graph as a “moderate pandemic,” but with increased clinical severity at 4.

Quadrant D is located in the upper right hand corner and the corresponding HHS pandemic planning scenarios are “severe pandemic” and “very severe pandemic.” Within this quadrant, influenza activity is characterized by moderate to very clinically severe (4 to 7 range) and moderate to high transmissibility (3 to 5 range). The 1918 pandemic is plotted on the graph as a “very severe pandemic,” with clinical severity at 7 and transmissibility at 5.

Quadrant C is located in the lower right hand corner and all four HHS pandemic planning scenarios are possible in this quadrant. In quadrant C, influenza activity is characterized by high clinical severity (4 to 7 range) and low to moderate transmissibility (1 to 3 range). No past flu seasons or pandemics are identified to fall within this range.