Lyophilized typhoid vaccine for intradermal use.

The prophylaxis of typhoid fever in Romania is usually achieved with fluid heat-killed phenolized vaccine. However the shelf life of this vaccine is only two years. The long term storage of an intradermal typhoid vaccine is made possible by lyophilization. A heat-inactivated bacterial suspension with a high concentration of organisms, at least 25 X 10(9) cells per ml, was freeze-dried at a temperature not higher than 30 degrees C. The final vaccine obtained had a residual moisture content of not more than 5%. Active and passive protection tests in mice, specific agglutinin production in humans and rabbits, the innocuity and the toxicity for mice, and the investigation of post-vaccinal adverse reactions in man, showed that the lyophilized typhoid vaccine could be stored at 4 degrees C for at least five years without loss of potency. Consequently, the vaccine may be stored without risk of deterioration for rapid emergency mass immunization with Jet-injector apparatus.