The World Health Organization cautioned that the virus might linger for a long time. “It is important to put this on the table: This virus may become just another endemic virus in our communities, and this virus may never go away,” said Mike Ryan, the head of the W.H.O. emergency response team. “This virus may become just another endemic virus in our communities, and this virus may never go away,” Mike Ryan, head of the organization’s health emergencies program, said at a news briefing. “H.I.V. has not gone away but we’ve come to terms with the virus and we have found the therapies and we have found the prevention methods, and people don’t feel as scared as they did before.” “There are no promises in this and there are no dates,” he said, tamping down expectations that the invention of a vaccine for the coronavirus will provide a quick and complete end to what has become a global health and economic calamity. A good vaccine might be developed, but there is no telling when, he added, calling it “a moon shot.” If infected people become immune or resistant, then when enough people have had the virus, there will be fewer left who can catch it or spread it, making outbreaks more manageable. But no one knows how long that will take.