A study found a national incidence of around 360 typhoid cases per 100,000 people, translating to approximately 4.5 million cases annually.

The Indian Council of Medical Research (ICMR) released an Expression of Interest (EoI) for companies to help validate and commercialise a new vaccine candidate developed by the National Institute for Research in Bacterial Infections (ICMR-NIRBI), Kolkata (erstwhile ICMR-NICED) that may help tackle enteric fever caused by both Salmonella typhi and S. paratyphi A.

Key features of the technology include:

• Isolation and Characterization of OMVs:

  • Outer Membrane Vesicles (OMVs) were isolated from Salmonella Typhi and Salmonella Paratyphi A.

  • These OMVs were comprehensively characterized to identify associated antigens, such as lipopolysaccharide (LPS) and Vi-polysaccharide.

• Immunization and Immune Response:

  • Adult mice were immunized orally with three doses of the bivalent OMV-based immunogen (25 μg/200 μl).

  • The immunization induced robust humoral responses, including significant serum IgG levels against LPS and Vi-polysaccharide.

  • It activated specific immune cell populations, such as CD4+, CD8+, and CD19+ cells, in the spleen of immunized mice.

  • The vaccine also stimulated Th1 and Th17 cell-mediated immune responses.

• Protective Efficacy:

  • Immunization with the bivalent OMVs provided protection against systemic infection caused by lethal doses of heterologous Salmonella strains in adult mice models.

  • The protective effect was found to be mediated by a combination of humoral and cell-mediated immune responses.

• Novel Mechanism of Protection:

  • Anti-OMVs antibodies generated through immunization significantly inhibited bacterial motility and their ability to penetrate mucin layers.

  • This new candidate vaccine is considered superior to the current typhoid conjugate and Vi-polysaccharide based vaccines, as the latter only protect against enteric fever caused by S. typhi strains.

  • The EoI now calls for companies to partner with ICMR on validating these results through vaccine trials and help develop and commercialise vaccines for use.

  • ICMR will provide funding and technical support through expert guidance for the same.