Background: The current study evaluated the reactogenicity and immunogenicity of Typherix, a recently developed Vi polysaccharide typhoid vaccine, in adolescents.
Methods: This phase II, open, single-group study was conducted at a single centre in South Africa. Healthy adolescents, aged between 11 and 18 years received a single 0.5ml dose of typhoid Vi polysaccharide vaccine 25 microg via intramuscular injection in the left deltoid. Safety and reactogenicity were assessed from solicited and unsolicited symptoms and signs reported during the 5-day and 28-day postvaccination follow-up periods. Seroconversion rates were calculated at 28 days after vaccination.
Results: A total of 100 adolescents received the vaccine. Seropositivity to Vi antigen was measured in 95 subjects and showed a rate of 98.9% [geometric mean titre (GMT) of 1966 enzyme-linked immunosorbent assay (ELISA) units/ml] at day 28. Of 99 subjects included in the reactogenicity analysis, 46.5% reported clinical symptoms, 40.4% general symptoms, and 18.2% local symptoms or signs. Solicited symptoms were reported in 46.5% of subjects. Local solicited symptoms involved mainly soreness. General solicited symptoms were most frequently headache (19% of subjects) and general aches (13%). All solicited symptoms were mild or moderate except for two reports of fever >39 degrees C. Unsolicited symptoms (all moderate) were recorded in 8.1% of subjects, and were most frequently of an upper respiratory tract nature and viral-like syndrome. No serious adverse events were reported.
Conclusions: The typhoid Vi polysaccharide vaccine Typherix proved to be well tolerated and immunogenic when administered to adolescents.