The rise of measles vaccination changed all that, and by 2000, the disease had been declared eliminated from the United States, after public-health officials detected no transmission of the virus for a full year. But now measles outbreaks are igniting across the country in communities where vaccination rates have dropped—most recently in South Carolina, where officials have documented more than 130 infections, nearly all of them among unvaccinated people. The U.S. has now clocked nearly a year of continuous measles transmission; come January, the country will very likely lose the elimination status that took nearly four decades of vaccination to gain.