E. H. LaBrec

Failure of Parenteral Vaccines to Protect Monkeys Against Experimental Shigellosis

Summary Monkeys injected subcutane-ously with either a combination of heat-killed or acetone-killed S. flexneri 2a vaccines or with vaccines made from living, virulent S. flexneri are not rendered resistant to experimental oral challenge with the homologous organism.

Biological properties of freeze-dried attenuated Shigella vaccines.

Summary Two Shigella flexneri 2 a strains of reduced virulence were lyophilized and their biological properties determined. When tested 19 to 23 months after drying for their ability to cause intestinal inflammation or death in starved guinea pigs, to produce keratoconjunctivitis, and to invade HeLa cells, reconstituted freeze-dried material acted in a manner similar to that of freshly grown bacteria. Reconstituted freeze-dried cells, used as oral vaccines, protected monkeys against experimental challenge with virulent S. flexneri 2a. There was no correlation between the ability to produce rises in circulating antibody and the capacity to protect against illness.