A single dose, combined vaccine against typhoid fever and hepatitis A: Consistency, immunogenicity and reactogenicity

Background:Vaccines against hepatitis A and typhoid fever are well established and have an excellent safety and immunogenicity profile. Yet these diseases, which share the same geographic distribution, remain an important cause of morbidity in travelers to endemic countries. Combined vaccination provides dual protection and improves compliance and coverage for travelers. Methods:This multicenter study evaluated the consistency of three lots of combined hepatitis A and typhoid fever vaccine. A total of 462 healthy subjects, aged 15-50 years, were enrolled and randomly allocated to 3 groups. The single dose of vaccine contains 25 mug typhoid Vi polysaccharide and at least 1,440 ELISA units of inactivated hepatitis A in a 1 mt dose. Results: Bioequivalence of all production lots was shown in terms of safety and immunogenicity. Pain at injection site was the most frequent reported local symptom, and headache was the most frequent reported general symptom. As early as 14 days after immunization >95% of the subjects were positive for anti-Vi antibodies and >86% were positive for anti-HAV antibodies. The GMTs and seropositivity rates were maintained during the 6 month follow-up. Conclusion:The first combined vaccine against typhoid fever and hepatitis A was safe and elicited a very good immune response, with the majority of subjects seropositive at 1 month for both antigens. This combined vaccine offered more convenience and rapid seroconversion to travelers.