The attenuated Salmonella strains used in the Vaxonella platform were acquired by Prokarium from Emergent BioSolutions in 2012 and are very safe and immunogenic vaccine delivery vectors, due to mutations in the aroC and ssaV genes. Salmonella enterica serovar Typhimurium strain WT05 is used in murine models to test the recombinant vaccine plasmids – these are then transformed into S. enterica serovar Typhi strain ZH9 for use in humans. ZH9 has completed five phase I and three phase II clinical trials as the typhoid vaccine Typhella®, dosed to over 400 volunteers (adults and children) and proven to be safe and well-tolerated. The SPI-2 mutation is in the ssaV gene of the type III secretion system used in invasion of host cells, which is illustrated below.

A clinical trial involving ZH9 was featured on the BBC News in May 2013 (see link).