- Immunocompromised subjects, including but not limited to subjects with: known human immunodeficiency virus infection (CD4 count < 200/mm3); known neutropenia (< 1500 neutrophils/mm3); chronic corticosteroid therapy (≥ 10 mg/day prednisolone therapy or equivalent for at least the past 3 months); immunosuppressant treatment, other than corticosteroids, within the previous 6 months; splenectomized subjects or subjects with known hyposplenia or asplenia.