Abstract
BackgroundSerotypes 22F and 33F have been added to a new pneumococcal-conjugate vaccine (PCV-15) because of their prevalence in causing invasive pneumococcal diseases (IPD). MethodWe measured anti-polysaccharide 22F, 33F, 19A and 6A antibodies in children before and after pneumococcal colonization and acute otitis media (AOM) episodes caused by these specific-serotypes. A two-step method for construction of correlate of protection (COP) models included using a generalized estimating equation for the relationship between antibody level, age and colonization history followed by logistic-regression modelling that included colonization or AOM episodes as independent variables, and age adjusted antibody level as the predictor. ResultsA vaccine-induced serum antibody level of 0.45 μg/ml for 22F, 0.51 μg/ml for 6A and 4.1 μg/ml for 19A correlated with prevention of pneumococcal colonization by respective serotypes (insufficient number of cases for 33F to find COP against colonization). Antibody levels of 0.25 μg/ml for 22F, 33F and 6A and 2 μg/ml for 19A correlated with prevention of AOM by the respective serotypes. ConclusionsA COP threshold of anti-22F, 33F, 19A and 6A serum antibodies for NP colonization and AOM in young children can be derived using GEE and logistic regression modelling.
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