Typhoid vaccination are of three types that are Whole-cell inactivated vaccines, Live attenuated oral vaccine (Ty2 1 strain), and parenteral Vi capsular polysaccharide vaccine. However, only the polysaccharide vaccine is currently available in Asian countries.
Contents: Each dose contains 25 mgIO.5 ml of capsular polysaccharide units (Vi antigen).
Supply & storage: It is supplied as single dose vials and should be stored at 2-8°C.
Dosage & administration: Irrespective of the age, 0.5 ml dose should be given deep SC/TM at age-appropriate sites.
Schedule of typhoid vaccination: Being a polysaccharide vaccine, it is not effective before 2 years of age. Subsequently, only single dose is required, with boosters at every 3-5 years. lAP recommends typhoid re-vaccinations every 3 years upto 18 years of age.
Protective value is . 70-80% for 5 years.
Side-effects of typhoid vaccination are rare, except local pain and erythema.
Other important issues:
• Whole cell inactivated typhoid vaccine, used earlier but not available at present, was a trivalent vaccine against typhoid, paratyphi A & paratyphi B (TAB vaccine).
Although cheaper, more protective (>80%) and effective at an earlier age (6 months onwards) than current polysaccharide vaccine, its production was stopped in late 80s due to high incidence of adverse effects. (Dose: 0.25 ml SC, 2 doses one month apart).
However, as these side-effects of typhoid vaccination were mainly due to paratyphoid components, lAP recommends reintroduction of whole-cell inactivated vaccines without paratyphi component in immunization schedule.
Adverse effects may be minimized by use of acetone-killed whole-cell vaccine rather than earlier phenol-heat inactivated vaccine.
• Oral typhoid vaccination is a live vaccine, which may be used only in children >6 years, as three doses of single capsule on alternate days. Entire schedule needs to be repeated at 3 years interval.
Protective efficacy is 70-80% for 5 years. Currently this vaccine is not marketed in India.
• Widal test reports should be interpreted with caution after typhoid vaccination, due to persistence of elevated ‘H’ titers for many years.