Given the substantial global burden of invasive pneumococcal disease, the introduction of protein conjugate pneumococcal vaccines may provide a useful option for protecting individuals at risk. Optimism stems from a large prospective study showing that a protein conjugate pneumococcal vaccine prevented 94% of invasive disease in young children.1 The clinical effectiveness of this vaccine now needs to be established among other children and adults at risk. These include people with increased exposure to Streptococcus pneumoniae , immunological defects due to HIV infection, bone marrow transplants, multiple myeloma, nephrotic syndrome, anatomical or functional asplenia, and older people with chronic conditions. The efficacy of the vaccine is unpredictable because the immune defects are different in each group. The need for a strict, objective assessment of the vaccine is further enhanced by serious concerns raised recently when this vaccine was unexpectedly found to increase the rates of pneumonia in HIV infected individuals.2 The lack of knowledge of the basic mechanism underlying pneumococcal vaccine failures indicates that adequate evidence should …