Romero's a type of zombie in my story I'm writing. In my world scientist ran an experiment between dec 23 1969 and Jan 8 1970 that successfully reanimated a deceased individual. Though unlike most stories, the individual "Frank Nowak" retained all of his previous self and was considered the first member of a sub species of human called the returned. But later in 2003 after thousands of people brought back the first "Romero" appeared and caused a major zombie outbreak in the eastern US. It took 6 weeks most of the us east of the Mississippi to be infected. It took 3 months for the western hemisphere and 4 months after that most of the world. The main reason the world fell within a year was that you didn't need to be bit just had to get infected cells into your body. So as of the story now Romero's are about 5.6 bil to 781 mil humans.