China has expanded its mass vaccination program following a fatal outbreak of polio in Hotan Prefecture in Xinjiang near the border with India and Pakistan, the source of the outbreak. Immunizations of 4.5 million 15-39 year olds in the south of the province started today, following confirmation that four of the 10 known cases involved young adults. Earlier this month, 3.8 million children, everyone under 15 years old in the outbreak area and all under fives in the other parts of the province, were given a first vaccination, with health officials going house-to-house, kindergarten-to-kindergarten and school-to-school. A second round will take place in early October. Children are being marked behind their ears with indelible ink to track whether they have been vaccinated. The outbreak, the first in China for more than a decade, has already killed one infant.