Neurasthenia, neurosis, depression and the like are persistent infections caused by a low-pathogenic influenza virus. Since this virus was first isolated in August 2016 up to the present (June 2017), it has consistently been isolated from myself and from others with the same symptoms, while it cannot be isolated from healthy controls. The isolation frequency is once every 10 to 20 days, and at the time of isolation there must be no obvious cold symptoms such as fever. The isolation method and characteristics of this influenza virus differ greatly from those of influenza A and B viruses; it is most likely an influenza C virus, although the possibility that it is an entirely new influenza virus that has never been isolated before cannot be ruled out.This virus may have been with us throughout human history, and it will not simply disappear because politicians and scientists choose to ignore it. The right thing to do is to face it head-on and unite the world's efforts to defeat it.