The infections are typically characterized by either meningitis or sepsis, and are caused by encapsulated organisms including Streptococcus pneumoniae.
[2][4] The disease progresses rapidly from the above mentioned symptoms to coma to refractory septic shock and finally death in as little as 24 hours.
[4] The spleen contains many macrophages (part of the reticuloendothelial system), which are immune cells that phagocytose (eat) and destroy bacteria.
These types of antibodies and complement are immune substances called opsonizers, molecules that bind to the surface of bacteria to facilitate phagocytosis.
When the spleen is no longer present (asplenia), IgG and C3b are still bound to bacteria, but they cannot be removed from the blood circulation due to the loss of the splenic macrophages.
[4][2] The Centers for Disease Control and Prevention's annual vaccine recommendations includes specifics for individuals without a functioning spleen.
The CDC recommends against live vaccines and has specific advice for travellers, which includes malaria avoidance for asplenic individuals.