Today the World Health Organization said trials of a single-dose Ebola vaccine, VSV-EBOV, that began in March were so successful that it would immediately extend vaccinations to "all people at risk" after contact with an infected person. The trial, which has shown 100% efficacy, included 4,000 close contacts of 100 Ebola patients. Half were vaccinated immediately and half were vaccinated three weeks after identification of an infected patient so results could be compared. Beginning this week, everyone will receive the vaccine at the same time. More research is needed and also more time to produce a supply of vaccine.