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Protective activity of Vi capsular polysaccharide vaccine against typhoid fever
K P Klugman1, I T Gilbertson, H J Koornhof
1Department of Medical Microbiology, University of the Witwatersrand.
Insights
A single dose of Vi capsular polysaccharide (CPS) vaccine provides significant protection against typhoid fever in children. This typhoid vaccination is safe, effective, and induces a sustained antibody response.
Area of Science:
- Immunology
- Vaccinology
- Infectious Diseases
Background:
- Typhoid fever remains a significant global health concern, particularly in developing regions.
- Effective vaccination strategies are crucial for controlling typhoid fever outbreaks.
- The Vi capsular polysaccharide (CPS) antigen is a key target for typhoid vaccines.
Purpose of the Study:
- To evaluate the protective efficacy and safety of a single intramuscular injection of Vi capsular polysaccharide (CPS) vaccine against typhoid fever.
- To assess the immunogenicity and duration of antibody response following Vi CPS vaccination.
- To compare the efficacy of Vi CPS vaccine with a control vaccine (meningococcal A + C CPS) and unvaccinated individuals.
Main Methods:
- A randomized, double-blind, controlled trial involving 11,384 children vaccinated with Vi CPS and a control group.
- 21 months of surveillance for blood-culture-proven typhoid fever cases.
- Measurement of anti-Vi antibodies using radioimmunoassay and enzyme-linked immunosorbent assay.
- Assessment of local side-effects post-vaccination.
Main Results:
- Vaccination with Vi CPS demonstrated significant protective efficacy against typhoid fever, ranging from 60% to 81% compared to control and unvaccinated groups.
- A substantial increase in anti-Vi antibodies was observed post-vaccination, with levels remaining elevated at 6 and 12 months.
- The Vi CPS vaccine was associated with minimal local side-effects, indicating a favorable safety profile.
Conclusions:
- A single intramuscular dose of 25 micrograms of Vi capsular polysaccharide (CPS) is a safe and effective typhoid vaccine.
- The vaccine induces a robust and sustained antibody response, crucial for long-term protection.
- Vi CPS vaccination represents a valuable tool for the prevention and control of typhoid fever.
Abstract:
The protective efficacy against typhoid fever of a single intramuscular injection of 25 micrograms of the Vi capsular polysaccharide (CPS) was assessed in a randomised double-blind controlled trial. Vaccination of 11,384 children was followed by 21 months' surveillance. 47 blood-culture-proven cases of typhoid occurred in children who received meningococcal A + C CPS vaccine and 19 cases in those vaccinated with Vi CPS. Protective efficacy was 60% calculated from the day of vaccination and 64% from 6 weeks after vaccination. Surveillance also included 11,691 unvaccinated children; 173 cases occurred in this group. Protective efficacy in relation to the unvaccinated group was 77.4% and 81.0% after 21 months, calculated immediately and 6 weeks after vaccination, respectively. Vaccination was associated with minimum local side-effects, and an increase in anti-Vi antibodies occurred, as measured by radioimmunoassay and enzyme-linked immunosorbent assay. Antibody levels remained significantly raised at 6 and 12 months post vaccination. Vi CPS is thus a safe and effective means of typhoid vaccination.