Development and validation of a multiplex bead assay and seroprevalence of IgG antibodies against 13 pneumococcal serotypes in United Kingdom children

Streptococcus pneumoniae causes significant global morbidity and mortality and is responsible for many cases of septicaemia, meningitis and pneumonia. Protective antibodies against capsular polysaccharides (> 90 serotypes) can be acquired naturally or induced by vaccination. In April 2010, a 7-valent conjugate vaccine (PCV7; serotypes 4, 6B, 9V, 14, 18C, 19F and 23F) was replaced by a 13-valent conjugate vaccine (PCV13; PCV7 serotypes plus 1, 3, 5, 6A, 7F and 19A) in the United Kingdom immunisation schedule. Response to vaccine can be evaluated by determining serotype-specific immunoglobulin G (IgG) antibody concentrations. The Vaccine Evaluation Unit of Public Health England currently use a multiplex fluorescent bead based assay to determine IgG concentrations for serotypes in PCV13 (excluding serotype 6A). In this thesis, this assay has been developed to include serotype 6A and successfully validated in terms of specificity, accuracy, reproducibility, linearity and stability. A seroprevalence study was conducted to test the assay, using sera from children aged < 4 years old in 2009 and 2012 (pre and post PCV13 introduction, respectively). Results showed no differences in antibody concentrations against serotypes present in both vaccines between 2009 and 2012. Additional serotypes in PCV13 had significantly higher geometric mean concentrations of IgG in 2012 compared to 2009, except for serotype 3, and an increase in the proportion of individuals with a protective antibody concentration ≥ 0.35 μg/mL. The 13-plex assay is a useful tool in assessing the effectiveness of PCV13.