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Summary
Early typhoid vaccines showed limited efficacy. Live oral vaccines, like Ty 21a, offer 95% resistance to typhoid fever for three years, but immunity is not absolute.
Area of Science:
- Microbiology
- Immunology
- Vaccinology
Context:
- Parenteral and oral typhoid vaccines were developed early but lacked prospective efficacy evaluations until the 1950s.
- Whole-cell parenteral vaccines demonstrated 60-90% efficacy for 3-5 years.
- Effectiveness of earlier oral killed typhoid vaccines remained unproven.
Purpose:
- To review the historical development and prospective evaluation of typhoid fever vaccines.
- To compare the efficacy of various typhoid vaccine formulations.
- To highlight advancements in live oral typhoid vaccines.
Summary:
- Acetone-inactivated and heat-phenol-killed parenteral vaccines showed 60-90% efficacy for 3-5 years.
- Live oral vaccines from avirulent mutants, such as Ty 21a, demonstrated superior effectiveness.
- The Ty 21a vaccine provided 95% resistance to clinical illness for three years in a field trial.
Impact:
- Typhoid vaccine development has progressed from less effective whole-cell preparations to more promising live oral attenuated strains.
- The Ty 21a vaccine represents a significant advancement in typhoid fever prevention.
- Understanding that immunity is not absolute is crucial for vaccinees to maintain hygiene practices.