Typhim Vi Mechanism of Action

Pharmacotherapeutic group: bacterial vaccines. ATC code: J07AP03.
Pharmacology: Pharmacodynamics: ANTI-TYPHOID VACCINE: This vaccine is prepared from purified Vi capsular polysaccharides of Salmonella typhi. Immunity appears between 1 to 3 weeks after the injection. Protection lasts around 3 years.
A double-blind, randomized, controlled efficacy clinical study was conducted in a highly endemic area in Nepal, in children and adults from 5 to 44 years. A total of 3,457 subjects received TYPHIM Vi. Compared with the control group (23 valence-pneumococcal polysaccharide vaccine), vaccine efficacy conferred by a single dose of vaccine TYPHIM Vi was 74% (CI 95%: 49; 87) against blood culture-confirmed cases of typhoid fever throughout the 20 months of active surveillance.
Seroconversion rate (defined as 4-fold rise of anti-Vi antibody levels) was collected in 19 clinical trials. These trials were conducted in endemic and non-endemic areas in adults and children from 2 years of age representing a total of 2,137 evaluable subjects. In the adult population, the seroconversion rate ranged from 62.5% to 100% four weeks after a single injection, with similar magnitude of anti-Vi immune response in non-endemic areas compared to endemic areas.
Anti-Vi antibody persistence depends on endemicity, with a trend for better persistence in endemic areas (documented up to 10 years in 83 children at levels equal or above 1 μg/mL considered as a serological indicator of protection against typhoid fever). In non-endemic areas, anti-Vi antibodies persist for 2 to 3 years with rates above 1 μg/mL around 41% after two years and 35.6% after 3 years of vaccination with TYPHIM Vi. Revaccination should be carried out with a maximum interval of 3 years if the subject is still exposed to the risk.
Paediatric population: In a double-blind, randomized, controlled efficacy clinical study conducted in a highly endemic area in South Africa, a total of 5,692 subjects from 5 to 15 years of age received TYPHIM Vi. Compared with the control group (meningococcal polysaccharide vaccine of groups A and C), vaccine efficacy conferred by a single dose of vaccine TYPHIM Vi was 55% (CI 95% : 30 ; 71) against blood culture- confirmed cases of typhoid fever during a 3-year follow-up.
Immunogenicity was assessed in both endemic and non-endemic areas in paediatric population aged from 2 to 17 years. In 9 clinical studies including 733 evaluable children, four weeks after a single injection of TYPHIM Vi, the seroconversion rate ranged from 67% to 100%, with a magnitude of anti-Vi immune response similar to that documented in adult.
Pharmacokinetics: Not applicable.
Toxicology: Preclinical safety data: Non-clinical data revealed no special hazard for humans based on conventional studies of acute toxicity, repeat dose toxicity, local safety and hypersensitivity.