The Knoxville Cough, also known as the Two Day Flu, the Sickness, the Asian Cough, and the Death Flu, among other names, is a virulent H5N1 strain of the avian influenza which emerged in 2021. It received its namesake from Knoxville, Tennessee where the disease was suspected to originate.
It is unknown how the influenza virus first came to be, though it was speculated that it first appeared in Knoxville, Tennessee in 2021. Initially the disease was regarded as simply a more virulent strain of the annual influenza until the severity of the outbreak had spread across the United States and other parts of the world. By July 2021 the Knoxville Cough caused more than 100,000 deaths worldwide and was officially labeled a pandemic by the World Health Organization. As the United States was already under a state of martial law, travel restriction were imposed in areas where cases of the influenza were identified, such as in St. Paul, Minnesota and Akron, Ohio.
Around this time, a governmental emergency broadcast stated that this national flu epidemic was in progress in all fifty states of America, and announced that although the U.S. government was attempting to develop a vaccine, the safest precaution for Americans was to stay indoors and avoid public meeting areas, and that hospitals were overloaded with flu cases, thus unable to accept more patients; the broadcast also mentioned dusk to dawn curfews for Albany, Elizabeth, Jersey City, Newark, New York, and White Plains.
By August 2022, the Knoxville Cough had ravaged various countries, with the United States particularly hard-hit (as its crumbling infrastructure and the high price of petroleum made the distribution of aid materials difficult and in some cases impossible), and by this point had killed six million Americans and in total at least eighteen million people around the world, though likely more, and was one of the factors sealing America's decline. At this point, though peak H5N1 activity had likely passed for most of the world, the virus still circulated in some regions into 2023. Furthermore, Mexico closed its borders to the U.S. to prevent the Knoxville Cough from coming into its country, although with promises to continue to provide material assistance. The President of the United States in his farewell address in 2025, shortly after the detonation of the GKR EMP blast across America, describes the Cough as "the most vicious pandemic in human history".
According to Homefront: The Voice of Freedom, it is briefly mentioned that there were rumors it was caused by an "engineered virus from an unfriendly nation", but such rumors were never actually proven.