The study is a double-blind (within dose level), placebo-controlled Phase I study to assess the safety, reactogenicity and tolerability of two intranasal dose levels of SynGEM®: a low dose level (140 μg F-protein/2mg BLPs) and a high dose level ( 350 μg F-protein/5mg BLPs), each administered twice according to a prime-boost schedule 28 days apart at Day 1 and Day 29. The two dose levels will be recruited sequentially.