The superflu is a plague that exterminates 99.4 % of the population of humans in The Stand. The virus, which causes the plague is also called Captain Trips. It will ignite the events of The Stand, which will lead to ultimate battle between good and evil in a post apocalyptic world.
The superflu was a biological weapon created by the American government, which got loose and spread across America and then the world. It had a 99.4% communicability rate and a 99% mortality rate. The US government forced news services to print and broadcast the official line, which was that there was nothing wrong going on, it was just the normal flue, and the situation was being under control.
Hospitals soon over filled to capacity and entire towns were quarantined as soldiers were deployed on the roads and highways, blocking off the entrances and exits. It wasn't long before evidence to the contrary began to spread. Photos, videos, and eyewitness accounts revealed to the world the truth. Soldiers dumping bodies into harbors from trucks and barge-trains full of plague victims that were towed out to the sea to be dumped.
Posters went up on college and university campuses throughout the country. Flyers that were variations on the theme of government complicity and cover-up with the superflu, which spread panic. Rebellious journalists, news staff, and talk radio broadcasters began to print and broadcast the truth, alerting the public to the lethal pandemic and the government coverup. To suppress the news, soldiers massacred protesting college students, executed news employees, and blew up the buildings of news broadcasters.
As the superflu wound down, there was a second epidemic of a sort. Within the United States, it killed approximately 16% of the survivors. Men, women, and children who were died of natural causes (e.g. heart attack), injuries that could not be treated (e.g. fractured skull), dangerous animals (e.g. bitten from a venomous snake), or their own actions (e.g. drug overdose).