Explanation:

Explanation

Context-Hyderabad-based Bharat Biotech has developed a typhoid vaccine (Typbar TCV) which has better efficacy than the previously used vaccinations in preventing typhoid fever.

• Typbar TCV is a type of conjugate vaccine which has already been pre-qualified by the World Health Organisation’s Strategic Advisory Group of Experts on Immunization (WHO-SAGE).
• This enables the procurement and supplies of this vaccine to UNICEF, Pan-American Health Organisation (PAHO) and GAVI-supported countries, the Hyderabad-based company said in a statement.
• Currently, two typhoid vaccines viz. Polysaccharide Typhoid Vaccine and Live, Weakened Typhoid Vaccine are used in India. However, their efficacy is lower than the conjugate vaccine as they offer 60-70% protection, unlike the conjugate vaccine which confers nearly 82% protection.

Typbar TCV

• The vaccine containing polysaccharide of Salmonella typhi Ty2 conjugated to Tetanus Toxoid. Vi Capsular polysaccharide of Salmonella typhi alone elicit B cell responses, but the conjugation of bacterial polysaccharide to a protein carrier provides foreign peptide antigens that are presented to the immune system eliciting antigen-specific CD4+ Th cells, referred to as T-dependent antibody responses. A hallmark of T-dependent responses, which are also elicited by toxoid is to induce both higher-affinity antibodies and long-term immune memory.
• Typbar TCV is the first typhoid vaccine, clinically proven to be administered to children from six months of age to adults and confers long term protection against typhoid fever
• Typbar TCV is the only approved vaccine for children and infants less than 2 years of age.

Typhoid

• Typhoid is caused by the salmonella typhi bacteria, and is spread through contaminated food and water. According to WHO, every year nearly 1.2 crore cases of typhoid are reported globally. Death from typhoid is put at more than 1.28 lakh globally each year. And this is mostly reported among children and young adults in Asia and sub-Saharan Africa.
• A typhoid conjugate vaccine offers a good solution to protect children from falling ill and from drug-resistant typhoid.

Conjugate vaccine

• Conjugate vaccines consist of antigens (polysaccharides or oligosaccharides) that are chemically coupled to a protein carrier (PC). Coupling of the saccharides to protein converts polysaccharides to T-dependent antigens, which elicit robust immune responses in infants and adults. These “glycoconjugate” vaccines elicit T-cell help for B-cells that produce IgG antibodies to the conjugated polysaccharide. Glycoconjugates thus induce PS-specific IgM-to-IgG switching, memory B-cell development, affinity maturation, and long-lived T-cell memory.