Vaccination & COVID 19

A conjugate vaccine is a type of subunit vaccine which combines a weak antigen with a strong antigen as a carrier so that the immune system has a stronger response to the weak antigen. The first glycoconjugate vaccine for use in humans, a Haemophilus influenzae type b (Hib) conjugate, was licensed in the USA in 1987 and shortly thereafter was introduced into the US infant immunization schedule. The success of the Hib conjugate vaccines in reducing the incidence of invasive Hib disease in childhood has accelerated the development of conjugate vaccines designed to prevent infection by other encapsulated bacteria. The imperative driving the development of such vaccines has been the need to find a vaccine formulation that renders bacterial capsular polysaccharides immunogenic in those most at risk of infection.

Pathogens such as Neisseria meningitidis serogroup C, Streptococcus pneumoniae and Hib are all major causes of childhood meningitis as well as other infection syndromes and have in common polysaccharide capsules (although of different structure) that act both as virulence determinants and targets for protective antibody. The importance of these pathogens in the young can partly be explained by the poor immunogenicity of some polysaccharides in this age group and the consequent inability of infants and young children to mount protective antibody responses. Vaccines containing Hib or pneumococcal capsular polysaccharides alone have thus failed to consistently protect this high risk group from infection