Lyophilized typhoid vaccine for intradermal use

Area of Science:

• Microbiology
• Immunology
• Vaccinology

Background:

• Current typhoid fever prophylaxis in Romania uses a heat-killed phenolized vaccine with a limited two-year shelf life.
• Long-term storage of vaccines is crucial for maintaining public health preparedness and emergency response capabilities.

Purpose of the Study:

• To develop and evaluate a lyophilized (freeze-dried) intradermal typhoid vaccine with an extended shelf life.
• To assess the stability, immunogenicity, and safety of the freeze-dried typhoid vaccine for potential mass immunization.

Main Methods:

• A heat-inactivated bacterial suspension (≥25 x 10^9 cells/ml) was freeze-dried at ≤30°C to achieve a residual moisture content of ≤5%.
• Potency was assessed through active and passive protection tests in mice, and immunogenicity was evaluated by measuring specific agglutinin production in humans and rabbits.
• Innocuity, toxicity in mice, and post-vaccinal adverse reactions in humans were investigated.

Main Results:

• The lyophilized typhoid vaccine demonstrated stability for at least five years when stored at 4°C without loss of potency.
• The vaccine induced specific agglutinin production in humans and rabbits, indicating immunogenicity.
• Tests showed the vaccine to be innocuous and non-toxic in mice, with minimal post-vaccinal adverse reactions in humans.

Conclusions:

• Lyophilization significantly enhances the long-term storage stability of intradermal typhoid vaccines, extending shelf life to a minimum of five years.
• The freeze-dried typhoid vaccine maintains potency and immunogenicity, making it a reliable option for emergency mass immunization, particularly with jet-injector devices.