Sir,. Typhoid fever is widely prevalent in India and three fairly good vaccines are currently available for protection viz.,. Whole-cell typhoid vaccine, ...
Typhoid Vaccination After Enteric Fever Sir, Typhoid fever is widely prevalent in India and three fairly good vaccines are currently available for protection viz., Whole-cell typhoid vaccine, Vi-polysaccharide vaccine, and Oral Ty21a vaccine. Booster doses of all the three vaccines are recommended after at least three years. 1 There are however, no clear guidelines on the issue of vaccination after an attack of enteric fever. If Vipolysaccharide vaccine, whole-cell vaccine, and Oral Ty21a vaccine induce an immunity lasting at least 3 years (boosters are recommended every 3-5 years), it is to be expected that infection by the whole organism would also induce an immunity lasting at least for the same duration. On the basis of theoretical grounds, it has been suggested that the oral vaccine might not add anything more to the gut-immunity induced by infection by the virulent S. typhi. 2 After an extensive literature-search, no recommendations and/or clinical studies could be located regarding this issue. One frequently comes across many children vaccinated against typhoid within 3 months of recovering from an attack of typhoid fever. Some authors have come across patients with recurrent typhoid fever,3but it seems to be a rare occurrence in clinical practice. Although it is clear that any child who suffers one attack of typhoid fever is at high risk for subsequent exposure in endemic countries,3
the practice of vaccinating for typhoid after such a short period of recovering from the illness appears to be flawed and is also not supported by clinical research. There is a need to carry out studies to determine the duration of immunity against re-infection, after an attack of typhoid fever. The Committee on Immunization of IAP should also consider the issue and put forward appropriate recommendations. Till such time it seems prudent that vaccination against typhoid should be done at least 3 years after an attack of enteric fever. Devendra Mishra Senior Research Associate, Department of Pediatrics, All India Institute of Medical Sciences, New Delhi-110029. E-maih dr_dmishra@rediffmaiLcom REFERENCES
1. Committee on Immunization. Parthasarthy A, Dutta AK, Bhave SY, eds. IAP Guidebook on Immunization. 2nd edn., Mumbai IndianAcademyof Pediatrics,2001;32-34. 2. JohnTJ. Typhoidvaccinationafterentericfever(reply).Indian Pediatr1999;36 : 724-725. 3. BhattaraiMD. Typhoid fever in children. Lancet 1999; 354: 2001-2002.
Author's Reply The author has raised an important issue regarding the guidelines of typhoid immunization following an attack of typhoid fever. It is recommended that typhoid vaccine may be given 3 months after recovery from an attack of fever. Pathogenesis of styphi clinical infection is complex in nature. The protective immune response is probably played by secretary intestinal antibody (in preventing mucosal invasion), circulating antibody (against bacteremic organism and cell mediated immunity (to eliminate intracellular bacilli). With parenteral vaccines, the circulating antibody response is substantial and provides the predominant protective effect. In contrast, with live attenuated oral vaccines, the circulating antibody response may be modest, but vigorous intestinal secretory immunoglobulin (sIgA) and cell mediated immunity occur that are believed to be responsible for protection. Unfortunately, with S. typhi the critical antigen responsible for protection is not agreed on and data are Indian Journal of Pediatrics, Volume 71mAugust, 2004
somewhat contradictory. With parenteral killed whole cell vaccine, elicitation of serum H (flageller) antibodies in human correlates with protection, whereas stimulation of O and vi antibodies does not. 1a~,4In contrast, with live oral vacines the mucosal IgA and systemic cell mediated immune response appear in large part to be directed toward the O and H antigen and not to the vi antigen. 5~'7'8'9 In fact the Ty21a live attenuated oral typhoid vaccine lacks vi antigen,1~yet provides significant protection. The term enteric fever is used to describe typhoid fever caused by S. typhi as well repenence parathyphoid fever caused by S. paratyphi A & B. If the diagnosis is in doubt whether it is typhoid or paratyphoid, there is full justification of giving typhoid vaccine after an interval of 3 months. However, doubt arises whether to vaccinate following an attack of typhoid fever. This leads to the question of comparison of vaccine derived immunity with natural immunity (acquired after typhoid fever). Several studies in the literature suggest that the 767
