Killed oral Shigella vaccine made from Shigella flexneri 2a protects against challenge in the rabbit model of shigellosis

The protective efficacy of an orally administered heat-killed virulent stra in of Shigella flexneri 2a (5 weekly oral doses) was evaluated in 25 rabbit s (14 immunized and 11 non-immunized controls) against challenge with the s ame strain of Shigella using the rabbit model of shigellosis. All 11 non-im munized rabbits developed bloody diarrhoea following challenge and 6 (54%) died. None of the 14 immunized rabbits developed diarrhoea (all had pellet stools) but 3 (21%) died from causes not associated with diarrhoea. Protect ion from diarrhoea and dysentery following oral immunization with a killed Shigella species was 100% and highly significant. Death following challenge was 2.5-fold higher in the non-immunized group (p = 0.115) but was not sig nificant. These promising results suggest that further studies should be un dertaken to develop a killed oral vaccine against shigellosis.