Vaccine Update :- Protection against enteric fever might be best achieved by a vaccine that stimulates IgG antibodies to "Vi" capsular polysaccharide in serum, IgG antibodies to "O" antigen in serum and cell mediated immune response. Live attenuated vaccine (Ty21a) is not able to elicit anti Vi antibodies may be because Vi expression is highly regulated. So new candidate vaccine - CVD-909 [oral attenuated typhoid vaccine] has been developed which expresses Vi antigen. In trials it induced both CD4 (+) and CD8 (+) mediated cell mediated immunity.

Safety concerns :- By and large both Vi Antigen polysaccharide & Ty21a oral vaccine are considered very safe and immunogenic but there may be few unexpected symptoms like dizziness and pruritis with Vi vaccine; fatigue and myalgia with Ty21a vaccine. In occasional cases reactive arthritis has also been reported.

IAPCOI stand on Typhoid vaccine :- IAPCOI strongly recommends use of this vaccine for all children. At present out of 3 types of vaccines (Vi polysaccharide, whole cell inactivated and oral Ty21a vaccine) only Vi vaccine is freely available in our country. It should be given to children above 2 years of age and after 3-5 years booster is required. In view of its high cost IAPCOI advocates its large scale manufacturing in public sector to reduce its cost.

WHO position on Typhoid vaccines :-

Both vaccines (Parenteral Vi based polysaccharide vaccine and live attenuated oral Ty21a) are of assured quality and safety. So the old heat inactivated whole cell vaccine should now be replaced by less reactogenic and equally efficacious modern vaccines.

Immunization of school age children and young adults in recommended in highly endemic areas where typhoid fever in these age groups is a significant public health problem, especially where antibiotic resistant S typhi strains are also prevalent. In these settings immunization with typhoid fever should be continued until socio-economic upliftment finally interrupt transmission of S. typhi. Typhoid vaccines can be given along with DPT vaccine wherever appropriate.

Neither the Vi based polysaccharide vaccine nor the Ty21a vaccine is licensed for children less than 2 years of age. However, while waiting for improved vaccines against enteric fever, further studies and trials are recommended to assess the protective efficacy of the currently licensed vaccines in the youngest age groups.