Table 1.

Characteristics of the 2 Typhoid Vaccines Currently Recommended by the World Health Organization: Ty21a and Vi Polysaccharide

	Ty21a Vaccine	Vi Capsular Polysaccharide Vaccine
Vaccine type	Live attenuated	Subunit
Composition	Chemically mutated Ty2 strain of S. typhi	Purified Vi capsular polysaccharide of Ty2 S. typhi strain
Immunogenic properties	▪Elicits mucosal IgA and serum IgG antibodies against O, H, and other antigens, as well as cell-mediated responses ▪No booster effect has been shown	▪Elicits serum IgG Vi antibodies ▪T-cell independent (no booster response)
Route of administration	Oral	Parenteral (subcutaneous or intramuscular)
Minimum age vaccine is licensed for use	2 years old for liquid formulation and 5 years old for capsule formulation	2 years old
Formulation	▪Enteric-coated capsules, or ▪Liquid suspension (lyophilized vaccine + buffer mixed with water upon use)	Solution of 25 µg combined with buffer
Number of doses required for complete vaccine regimen	3 to 4	1
Storage requirements	Requires storage at 2º to 8ºC	Requires storage at 2º to 8ºC
Shelf life in higher temperature	14 days at 25 °C	6 months at 37 °C 2 years at 22 °C
Safety/tolerability	High	High
Efficacy at 3 years (95% CI)	51% (36–62%)	55% (30–70%)
Length of protection	At least 5–7 years	At least 3 years

Abbreviations: CI, confidence interval; Ig, immunoglobin; S. typhi, Salmonella enterica serovar typhi.