On Apr. 15, 2009, a novel influenza A virus (then referred to as ‘swine origin influenza A virus’) was first detected in a 10-year-old patient in California, who was tested for influenza as part of a clinical study. Laboratory testing at CDC confirmed that this virus was new to humans, and it spread quickly across the country and the world.

This new H1N1 virus contained a unique combination of influenza genes not previously identified in animals or people.