This highly contagious disease, typhoid fever (or abdominal typhoid), is caused by the bacterium Salmonella Typhi, which is transmitted by ingesting infected food. Symptoms include fever, abdominal pain and, in some cases, diarrhea and intestinal bleeding.

The disease is endemic in many developing areas of Africa, Central and South America and Asia, where it is a serious public health problem. The WHO estimates between 11 and 20 million cases each year, and continued urbanisation and climate change could cause the incidence to increase further.

In the case of the oral formulation, 3 tablets must be taken every other day (so day 1, day 3, and day 5), and protection begins about 10 days after the last dose. There is 1 dose for the intramuscular formulation, to be administered at least 2 weeks before potential exposure.

The oral formulation is composed of the live attenuated strain Ty21a, while the intramuscular formulation contains purified capsular polysaccharides (the molecules that make up the outer structure of the bacterium) of strain Ty2.