Conjugate vaccines

conjugate vaccines

1. CONJUGATE VACCINES Presented by Anusiya G (18MBT015)

2. Introduction A conjugate vaccine is a substance that is composed of a polysaccharide antigen fused to a carrier molecule. Designed by chemically linking a sugar chain with peptide antigen. Polysaccharide antigens on the surface of the bacterial cells are covered by slime layer thus remain protected from WBCs in human blood. Besides, the immature immune systems of very young people eg . Babies, children often have difficulty recognizing certain polysaccharide antigens . For establishing immunity through overcoming these problems where ordinary vaccines may not be effective, conjugate vaccines become a choice of interest.

3. A conjugate vaccine is created by covalently attaching a poor antigen (polysaccharide ) to a strong antigen (protein) thereby eliciting a stronger immunological response to the poor antigen . However peptide/protein and protein/protein conjugates have also been developed. For example, Haemophilus influenzae type B ( Hib ) Vaccine. Pneumoccocal Vaccine. Meningococcal Vaccine.

4. History The idea first appeared in experiments involving rabbits in 1927. The first conjugate vaccine (   Haemophilus influenzae  type b ( Hib ) ) used in humans became available in 1987 .  This was theconjugate , which protects against  meningitis . The vaccine was soon incorporated with the schedule for infant immunization in the United States.  Soon after the vaccine was made available the rates of Hib infection dropped, with a decrease of 90.7% between 1987 and 1991 .  Infection rates diminished even more once the vaccine was made available for infants.

5. Comparison

6. Mechanism

7. For bacteria with a polysaccharide coating, the immune response creates  B cell s independent of  T cell  stimulation . Polysaccharide + protein carrier=> T cell responce   . P olysaccharides -cannot be loaded onto the   MHC of  APC, because   MHC  can only bind peptides whereas conjugate vaccines can be loaded. This promote a more rapid and long-lasting immunologic memory . This conjugation - increases efficiency of the vaccine as a non conjugated vaccine against the polysaccharide antigen is not effective in young children .  By combining the bacterial polysaccharide with another antigen, the immune system is able to respond.

8. Implementation Haemophilus influenzae B ( Hib ) The first glyco conjugate vaccine for use in humans, a Haemophilus influenzae type b ( Hib ) conjugate licensed in USA in 1987. Hib is a major cause of meningitis in children <5 years old as well as a cause of pneumonia. Formulations of Hib conjugates with different protein carriers including tetanus toxoid , diphtheria toxoid , mutant diphtheria toxin and outer membrane protein have been developed and vary both quantitatively and qualitatively in their immunogenicity.

9. Implementation Streptococcus pneumoniae There are current three vaccines in use for the prevention of S.pneumoniae , consisting of 10 and 23 polysaccharides conjugated to H.influenzae or diphtheria carrier proteins . The polysaccharides that cover bacteria vary greatly even within a single species of bacteria . In Streptococcus pneumoniae there are more than 90 different serotypes due to variation in the bacterial polysaccharide coat. Therefore , polysaccharide vaccines often consist of a panel of polysaccharides to increase protection.

10. ADVANTAGES These vaccines are cost effectives . Improved immune and memory response Longer lasting protection Prevents asymptomatic Carriage of Disease. Pathogens that remain protected by encapsulation are destroy , so vaccination is possible against encapsulated bacteria.

11. DISADVANTAGES Preparation is more complex and complicated. Vaccine may cause mild side effects, these includes slight fever , allergic reaction, tenderness, swelling and redness at the site of the shot. Loss of immunogenicity during conjugation. Immunogenic response is restricted to selected antigens.