The initial part of the study was designed to determine the dose and safety of the individual vaccines using an open-label dose escalation method. Study volunteers were randomly allocated to two groups of four that received 5 x 10^7 pfu id of either FP9 CS or MVA CS. When a good safety profile was evident one week after this dose, another set of four volunteers per group received a higher dose (1 x 10^8 pfu id) of FP9 CS or MVA CS. After the investigators had achieved a satisfactory safety profile with a higher dose of both vaccines given alone, they proceeded to administer the vaccines in combination using the heterologous prime-boost regime. The vaccines were administered at 4-week intervals. Eight volunteers received FP9 CS at week 0 followed by MVA CS at week 4 (FM group). Another set of 8 volunteers received FP9 CS at weeks 0 and 4, followed by MVA CS at week 8 (FFM). Following vaccination, volunteers were observed for 1 hour and given a course of antipyretic (paracetamol) to take if required. A physician and a study nurse could be contacted by the volunteers at anytime during the course of the study. In addition, home visits were made by field workers on days 1, 2, 7 and 28, after each vaccination, to record adverse events using a standard questionnaire.