No virus is more feared than Ebola. So scientists were alarmed when a new species of Ebola emerged in Uganda in 2007.
They worried that the Bundibugyo ebolavirus, as it's called after the township in western Uganda where it was discovered, wouldn't be thwarted by the promising experimental vaccines already being developed against other lethal Ebola species.
Scientists can't just keep adding new viral species or strains to vaccines. "Generally the more strains you put into a vaccine, the less likely it will work," says vaccine researcher Nancy Sullivan of the National Institute of Allergy and Infectious Diseases.