More than 1,300 people in South Korea are under mandatory quarantine as health officials scramble to contain the largest outbreak of Middle East respiratory syndrome, or MERS, outside the Arabian Peninsula. So far, at least 30 people in South Korea have contracted the virus, which has no known vaccine or cure. Two of them have died since the outbreak began May 20.
Scientists are trying to figure out why a single imported case led to so many secondary infections.