A New Vaccine in the Fight Against Typhoid Fever

Posted 9 November 2017

This blog post was written Margot Groves Robinson of Stanford University who is attending the ASTMH Annual meeting as a Benjamin H. Kean Travel Fellow in Tropical Medicine

Rising rates of antimicrobial resistance have made typhoid fever “essentially an untreatable disease” in parts of the world where broad spectrum treatments are inaccessible, said Dr. Kathleen Neuzil of the University of Maryland School of Medicine at a session at TropMed17 today. However, the fight against typhoid fever has recently gained a new weapon, the Typhoid Conjugate Vaccine (TCV).
Typhoid fever is a serious public health challenge that infects more than 20 million people each year, primarily in Asia and sub-Saharan Africa, and accounts for 222,000 deaths annually. It is a systemic bacterial infection caused by Salmonella Typhi, usually through eating contaminated food or water. Illness can be characterized by fever, headache, nausea, and loss of appetite.
Just last month, the TCV was officially recommended by the WHO SAGE Working Group on Typhoid Vaccines for administration to children 6 months of age and older2.
To compare the conjugate vaccine’s effectiveness against the current standard polysaccharide vaccine, Dr. Andrew Pollard of Oxford University had conducted a human challenge model test at the Centre for Clinical Vaccinology and Tropical Medicine in Oxford. According to Dr. Pollard, human challenge models, in which healthy volunteers are deliberately infected with infectious agents and monitored for symptoms, allow for studies of vaccine efficaciousness without requiring large numbers of volunteers.
The 112 participants were randomly assigned to receive a conjugate typhoid vaccine, a standard polysaccharide typhoid vaccine, or a control vaccine. Published in the Lancet in September, the study results showed similar efficacies between the conjugate versus the polysaccharide vaccine (54.6% versus 52.0%1), indicating that the TCV is at least as efficacious as the standard polysaccharide vaccine.
Interestingly, the odds of viral shedding were found to be three times lower for subjects vaccinated with TCV as compared with the polysaccharide vaccine, which is exciting evidence that the new vaccine may be able to bolster herd immunity in endemic areas.
It is an exciting time for typhoid disease prevention, and more information will continue to become available in the coming weeks and months.