Within each cohort, in an observer-blind fashion, subjects will be randomized to receive three vaccinations, four weeks apart, of either 1790GAHB vaccine (at five antigen concentrations) or GAHB placebo. A Data Safety Monitoring Board will be in place to receive a summary of all safety data obtained during one week follow-up post-first vaccination with the lower dose. Based on evaluation of the safety data, the Data Safety Monitoring Board will make a recommendation, as to whether the next cohort should be vaccinated with higher antigen concentration or not.