I got a random event in the game, I assume it was a mega event, where a plauge strikes everyone. I was told the only hope for each civilization is to research "cure plauge" or "plauge cure". I went into the research screen and it didn't show up on the list. I then looked on the tech tree link window on the same screen but at the bottom. I was able to find it and click on it and research it that way. I already had the prerequiste for it.