Reactogenicity and immunogenicity of a single dose of typhoid Vi polysaccharide vaccine in children aged between 4 and 14 years

Background: The current study evaluated the reactogenicity and immunogenicity of Typherix(TM),(2) a new typhoid Vi polysaccharide vaccine, in children aged between 4 and 14 years. Methods: This phase III, open, single-group study was conducted at a single centre in South Africa. Healthy children aged between 4 and 14 years received a single 0.5ml dose containing typhoid Vi polysaccharide vaccine 25 mug via intramuscular injection in the left deltoid. Safety and reactogenicity were assessed from solicited and unsolicited signs and symptoms reported during the 5- and 28-day postvaccination follow-up periods. Seropositivity rates against Vi were calculated at 28 days and 6 months after vaccination, and geometric mean titres (GMTs) were also calculated. Results: A total of 199 children received the vaccine. The according-to-protocol immunogenicity analysis included 185 subjects and showed seropositivity rates of 99.5% [GMT of 2578 enzyme-linked immunosorbent assay (ELISA) units/ml] at day 28 and 94.5% (GMT of 1022 EL.U/ml) at 6 months. Of the 199 subjects included in the reactogenicity analysis, 52.8% reported clinical symptoms, 50.3% reported general symptoms, and 4.0% local symptoms. Solicited symptoms were reported in 46.7% of subjects. Local symptoms and signs were mild and involved mainly swelling. General solicited symptoms were most frequently fever (31.7% of subjects) and headache (14.1%). All general solicited symptoms were mild or moderate except for four reports of fever >39 degreesC. Unsolicited symptoms (mild or moderate) were recorded in 25.1% of subjects, and were most frequently abdominal pain and coughing. No serious adverse events were reported. Conclusions: Typherix(TM) typhoid Vi polysaccharide vaccine proved to be well tolerated and immunogenic when administered parenterally to children aged between 4 and 14 years.