Mild phenotype: Multiple serotypes (> 50% for children 2 to 5 years or > 30% for patients 6 to 65 years) without protective titers or without a 2-fold increase in titers Moderate phenotype: Protective titers to ≥ 3 serotypes but fewer than the expected number for their age Severe phenotype: Protective titers to ≤ 2 serotypes, and the titer, if present, tends to be low (< 1.3 - 2.0 microg / mL [< 1.3 - 2.0 mg / L]).