Comparative tolerability and immunogenicity of Typherix or Typhim Vi in healthy adults: 0, 12-month and 0, 24-month administration

This study was carried out to compare the immunogenicity and tolerability of Typherix, a recently developed typhoid Vi polysaccharide vaccine, with Typhim Vi, the first available Vi polysaccharide vaccine, in healthy adults. Three different production lots of Typherix were also compared. All subjects were randomised to receive an initial dose of Typhim Vi, or one of three production lots of Typherix, and subsequently randomised to receive a second dose of vaccine at 12 or 24 months. Adverse events were recorded by patients for 6 days after vaccination. Anti-Vi antibodies were measured in serum on days 0, 7, 14 and 28, at months 6, 12 and 24, and 1 month after the second dose (month 13 or 25). A total of 400 healthy subjects aged between 18 and 50 years received the first dose of vaccine. Significantly fewer patients in the three Typherix groups than in the Typhim Vi group reported adverse events (17 to 21% vs 44%, respectively). Seropositivity rates were 95.7 to 97.9% among subjects in the three Typherix groups at day 14, and 96.8% in the Typhim Vi group (no significant between-group differences). The only significant difference between the vaccines in seropositivity was observed at day 7 (71.8% for Typherix vs 86.4% for Typhim Vi). Of subjects receiving the second dose of Typherix at 12 and 24 months, 77% and 61% were seropositive before revaccination, compared with 69% and 46% for Typhim Vi (no significant difference). There were no significant differences in seropositivity or adverse events between the two vaccines after administration of the second dose (12 or 24 months). The initial dose of Typherix was associated with fewer adverse events than Typhim Vi. On the basis of serum Vi titres, the two vaccines demonstrated equivalent immunogenicity, with 0, 12-month and 0, 24-month administration. There were no differences between the three different production lots of Typherix.