Bivalent conjugate vaccines for typhoid and paratyphoid fever


Rubhana Raqib


Enteric fever is caused by Salmonella enterica serovars Typhi and paratyphi serovars Paratyphi A, Paratyphi B, and Paratyphi C that can cause severe and sometimes life-threatening systemic bacterial infection in humans. Clinical features are indistinguishable between the two serovars and humans are the only known reservoir. Risk for infection is high in low-income and lower-middle-income countries, particularly in south and southeast Asia in settings where there is scarce access to safe water and poor sanitation systems. Over a quarter of all cases of enteric fever in Asia are attributable to Paratyphoid A with an estimated 3·39 million cases of paratyphoid fever occurring globally and an estimated 19 108 deaths. Moreover, the burden of paratyphoid disease is progressively increasing. Treatment with antibiotics can reduce death; however, treatments for both typhoid and paratyphoid fever can often become complicated and expensive due to heightened rates of resistance to multiple antimicrobials. For both types of fever, vaccination is the best preventive measure other than safe food and water intake and good hygiene practices. Three types of licensed vaccines are available for typhoid fever (typhoid conjugate vaccines [TCVs], typhoid vaccine live oral Ty21a, and Vi capsular polysaccharide vaccines). However, no licensed vaccines are yet available against paratyphoid fever. Despite major progress made in the availability of different typhoid vaccines, particularly the conjugate vaccines, preventing typhoid fever alone will not be effective in combating overall enteric fever if paratyphoid fever is also not contained.

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