Typhoid vaccines are known to the medical science for more than a century. Wright in 1896 introduced typhoid vaccine for the first time. Vi polysaccharide of S. typhi was recognized as the only important antigen involved in inducing protective antibodies Felix & Pitt(1935).The new type of typhoid vaccines were developed by reexamination of the protective role of the capsular polysaccharide (Vi antigen) Robbins J.D., Robbins J.B.(1984).
Vi Polysaccharide typhoid vaccine
Vi antigen also called as the virulence antigen of Salmonella typhi has been described as an important antigen capable of inducing immune response in children >2 years of age. Extensive clinical trial conducted in Nepal showed that the Vi polysaccharide is immunogenic and efficacious.
This vaccine was introduced in India in 1995.It contains a very small component of the outer layer of the bacteria (Vi polysaccharide), which provides high degree of protection , with almost minimal adverse effects profile. Additionally instead of two injections with whole cell type vaccine ,Vi polysaccharide typhoid need only one injection. This vaccine provides protection which lasts for at least 2 years. Hence booster injection is recommended every 3 years.
Since Vi Polysaccharide typhoid vaccine does not induce immune response in infants and children below 2 years of age, hence they had remained unprotected against typhoid fever so far.
Research by Szu, S.C. et al. (1987),Kossaczka Z.et al.(1997,1999) led to the development & availability of Vi conjugate typhoid vaccine in India (Peda TyphTM) for the first time in the world by Bio-Med (P) Ltd.
Vi conjugate typhoid Vaccine -Peda TyphTM
The need to find an alternative has been on for past several years. The scientists of the N.I.H.,U.S.A. & the A.I.I.M.S., New Delhi, India had been successful in developing Vi polysaccharide conjugated with recombinant protein antigens e.g.
- Recombinant exotoxin A of P.aeruginosa.
- ‘OMP’ of S.typhi produced in E.Coli.
Research by Szu, S.C. et al .(1987),Kossaczka Z.et al.(1997,1999) led to the development and availability of Vi conjugate typhoid vaccine in India (Peda TyphTM) and for the first time in the world.
BIO-MED scientists have developed a unique process of conjugation using a time tested natural protein Tetanus toxoid. This method has proved very effective and safe as tested in animal studies and in the multicentric clinical trials on infants, children and adults.
The Vi conjugated typhoid vaccines have been demonstrated to induce ‘T’ cell dependent response with much higher antibody levels providing protection in >90% Lin F.Y.et al .(2001), Lanh M.N. et al.(2003).
The Peda Typh TM availability promises control of typhoid in infants, children and adults. This vaccine is amenable to booster vaccination and is expected to confer much better grade immunity in much higher percentage of vaccinees.