Immunogenicity of a Bivalent Typhoid-Paratyphoid Conjugate Vaccine Against Diverse Salmonella Paratyphi A Isolates.
Martina Carducci, Eleanna Sarakinou, Luisa Massai et al.
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In 30 seconds
This exploratory analysis of a phase 1 randomised controlled trial assessed O:2-specific IgA and IgM responses and serum bactericidal activity after two doses of a bivalent typhoid-paratyphoid conjugate vaccine. It included 46 participants who received vaccine with or without alum, 169 days apart. Both formulations elicited IgA, IgM and bactericidal responses against diverse Salmonella Paratyphi A isolates; responses were higher without alum. At day 29 after dose 1, IgA rose 74.14-fold without alum and 16.65-fold with alum, and remained above baseline through day 197.
Key findings
- At day 29 after dose 1, O:2-specific IgA rose 74.14-fold without alum and 16.65-fold with alum.
- The nonadjuvanted formulation produced significantly higher IgA responses and bactericidal activity at day 29 (P < .05).
- Anti-O:2 IgM strongly correlated with bactericidal antibodies against homologous and heterologous S Paratyphi A strains.
- Both formulations elicited IgA responses that remained well above baseline through day 197.
Why it matters
The findings extend evidence of vaccine immunogenicity beyond the vaccine-homologous strain, showing bactericidal activity against diverse S Paratyphi A isolates. The association between IgM and bactericidal antibodies also supports its relevance as an immune-response marker. These results inform further evaluation of a bivalent vaccine intended to address typhoid and paratyphoid, while remaining early-phase immunogenicity evidence rather than proof of clinical protection.
What to keep in mind
This was an exploratory analysis of 46 participants in a phase 1 trial; immune responses were measured, not clinical protection.