In a single-centre , double-blind phase 1/2a study , young volunteers ( aged 18-28 years ) were randomly assigned with a computer-generated list in equal numbers to one of eight groups and were given one injection or two injections intramuscularly at an interval of 4 weeks of a standard dose ( 10 ( 8 ) plaque forming units [ pfu ] ) or a ten times lower dose ( 10 ( 7 ) pfu ) of the MVA-H5-sfMR ( vector encoding the haemagglutinin gene of influenza A/Vietnam/1194 / 2004 virus [ H5N1 subtype ] ) or MVA-F6-sfMR ( empty vector ) vaccine .