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Efficient vaccination strategy against typhoid fever
Vaccine 18 (2000) 2321
www.elsevier.com/locate/vaccine
Letter to the editor Ecient vaccination strategy against typhoid fever Quanti®cation of antibody response to Salmonella typhi Vi polysaccharide vaccine, Typhim Vi1, in HIVinfected individuals revealed that typhoid polysaccharide antigen Vi was a T-cell independent type 2 antigen [1]. The immune response in the recipient of the vaccine was dependent on the number and function of Tlymphcytes, severely curtailed during an HIV infection. Undoubtedly, further investigations would be required to improve the antigenicity of the future immunogen that would not depend on the number and function of T-lymphocytes. Such an immunogen would as well address vast populations in developing countries where protein-calorie malnutrition, vitamin A de®ciency exist simultaneously and lead to severe numerical and functional defect in T-lymphocytes [2]. Prospective S. typhi polysaccharide Vi antigen based vaccine formulations even if they were not relying on T-lymphocyte number and functional competence, might not protect against S. typhi infections by bacterial isolates lacking Vi antigen. Infection with such strains, that cause a disease indistinguishable from the Vi-positive strains [3], would not be protected by Vi polysaccharide vaccine, existing Typhim Vi1, or the future generation improved formulations. The ecient formulations would be useful only if they tackle typhoid episodes by Vi-positive and Vi-negative S. typhi strains. Typhoid fever is reported to spare children aged 6 months to 3 years [4]. That has been confounded by precise, clinical and microbiological investigations in an urban poor area in India, when the incidence of typhoid fever was highest in the age group under 5 years of age in relation to those aged 5±19 years and between 19 and 40 years [5]. Prospective typhoid immunization of masses using the oral typhoid vaccine, Ty21a alone or the combined oral, bivalent, CVD 103HgR/Ty21a for cholera and typhoid [6], would not be of much use in infants or children under 5 years of age. Oral vaccine, Ty21a is not recommended in chil-
dren aged less than 6 years [7]. Furthermore, it is not indicated in those with immune suppression [7]. To conclude, ®scal input to produce a better vaccine against typhoid that would not fare poorly in those with poor T-cell function [1,2], and tackle infection by Vi-negative S. typhi strains eciently would prove more than cost-eective. Ideally, a single dose oral vaccine would be successful for mass prophylaxis in infants and young children. A liquid formulation like the Sabin live poliovirus vaccine would be successful in children as they would resent any preparation, like the gelatin capsule formulation of Ty21a [7]. The rising incidence of typhoid fever in endemic and non-endemic areas would be mitigated only through a future T-lymphocyte independent, oral, rather broad spectrum preparation. References [1] Kroon FP, van Dissel RJ, Rovensbergen E, Nibbering PH, van Furth R. Impaired antibody response after immunization of HIV-infected individuals with the polysaccharide vaccine against Salmonella typhi (Typhim Vi1). Vaccine 1999;17:2941±5. [2] Semba RD, Muhilal, Ward BJ, et al. Abnormal T-cell subset proportions in vitamin-A de®cient children. Lancet 1993;341:5±8. [3] Hornick RB, Gresiman SE, Woodward TE, et al. Typhoid fever: pathogenesis and immunological control (second of two parts). N Engl J Med 1970;283:686±91. [4] Mahle WT, Levine MM. Salmonella typhi infection in children younger than ®ve years of age. Pediat Infect Dis J 1993;12:627± 31. [5] Sinha A, Sazawal S, Kumar R, et al. Typhoid fever in children aged less than 5 years. Lancet 1999;354:734±7. [6] Foster RH, Noble S. Bivalent cholera and typhoid vaccine. Drugs 1999;58:91±6. [7] Physicians' Desk Reference, 52nd ed. Montvale: Medical Economics Company, 1998.
0264-410X/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 4 - 4 1 0 X ( 0 0 ) 0 0 0 1 4 - 1
Subhash C. Arya Centre for Logistical Research and Innovation, M-122, (of part 2), Greater Kailash II, New Delhi, 110048, India E-mail address: [email protected]
www.elsevier.com/locate/vaccine
Letter to the editor Ecient vaccination strategy against typhoid fever Quanti®cation of antibody response to Salmonella typhi Vi polysaccharide vaccine, Typhim Vi1, in HIVinfected individuals revealed that typhoid polysaccharide antigen Vi was a T-cell independent type 2 antigen [1]. The immune response in the recipient of the vaccine was dependent on the number and function of Tlymphcytes, severely curtailed during an HIV infection. Undoubtedly, further investigations would be required to improve the antigenicity of the future immunogen that would not depend on the number and function of T-lymphocytes. Such an immunogen would as well address vast populations in developing countries where protein-calorie malnutrition, vitamin A de®ciency exist simultaneously and lead to severe numerical and functional defect in T-lymphocytes [2]. Prospective S. typhi polysaccharide Vi antigen based vaccine formulations even if they were not relying on T-lymphocyte number and functional competence, might not protect against S. typhi infections by bacterial isolates lacking Vi antigen. Infection with such strains, that cause a disease indistinguishable from the Vi-positive strains [3], would not be protected by Vi polysaccharide vaccine, existing Typhim Vi1, or the future generation improved formulations. The ecient formulations would be useful only if they tackle typhoid episodes by Vi-positive and Vi-negative S. typhi strains. Typhoid fever is reported to spare children aged 6 months to 3 years [4]. That has been confounded by precise, clinical and microbiological investigations in an urban poor area in India, when the incidence of typhoid fever was highest in the age group under 5 years of age in relation to those aged 5±19 years and between 19 and 40 years [5]. Prospective typhoid immunization of masses using the oral typhoid vaccine, Ty21a alone or the combined oral, bivalent, CVD 103HgR/Ty21a for cholera and typhoid [6], would not be of much use in infants or children under 5 years of age. Oral vaccine, Ty21a is not recommended in chil-
dren aged less than 6 years [7]. Furthermore, it is not indicated in those with immune suppression [7]. To conclude, ®scal input to produce a better vaccine against typhoid that would not fare poorly in those with poor T-cell function [1,2], and tackle infection by Vi-negative S. typhi strains eciently would prove more than cost-eective. Ideally, a single dose oral vaccine would be successful for mass prophylaxis in infants and young children. A liquid formulation like the Sabin live poliovirus vaccine would be successful in children as they would resent any preparation, like the gelatin capsule formulation of Ty21a [7]. The rising incidence of typhoid fever in endemic and non-endemic areas would be mitigated only through a future T-lymphocyte independent, oral, rather broad spectrum preparation. References [1] Kroon FP, van Dissel RJ, Rovensbergen E, Nibbering PH, van Furth R. Impaired antibody response after immunization of HIV-infected individuals with the polysaccharide vaccine against Salmonella typhi (Typhim Vi1). Vaccine 1999;17:2941±5. [2] Semba RD, Muhilal, Ward BJ, et al. Abnormal T-cell subset proportions in vitamin-A de®cient children. Lancet 1993;341:5±8. [3] Hornick RB, Gresiman SE, Woodward TE, et al. Typhoid fever: pathogenesis and immunological control (second of two parts). N Engl J Med 1970;283:686±91. [4] Mahle WT, Levine MM. Salmonella typhi infection in children younger than ®ve years of age. Pediat Infect Dis J 1993;12:627± 31. [5] Sinha A, Sazawal S, Kumar R, et al. Typhoid fever in children aged less than 5 years. Lancet 1999;354:734±7. [6] Foster RH, Noble S. Bivalent cholera and typhoid vaccine. Drugs 1999;58:91±6. [7] Physicians' Desk Reference, 52nd ed. Montvale: Medical Economics Company, 1998.
0264-410X/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 4 - 4 1 0 X ( 0 0 ) 0 0 0 1 4 - 1
Subhash C. Arya Centre for Logistical Research and Innovation, M-122, (of part 2), Greater Kailash II, New Delhi, 110048, India E-mail address: [email protected]