Distinguish between Antigen and antibody, Active immunity and passive immunity, and explain why the body does not develop full immunity against some diseases like malaria.

• Antigen: A foreign substance, usually a protein or polysaccharide, that triggers an immune response in the body, leading to the production of antibodies.
• Antibody: A protein produced by plasma cells (a type of B lymphocyte) in response to an antigen. Antibodies specifically bind to antigens to neutralize them or mark them for destruction by other immune cells.

• Active immunity: Immunity developed when an individual's own immune system produces antibodies in response to an antigen, either through natural infection or vaccination. It is long-lasting.
• Passive immunity: Immunity acquired by an individual receiving antibodies produced by another organism. This immunity is immediate but temporary, as the body does not produce its own antibodies (e.g., antibodies passed from mother to child, or through antiserum injection).

The body does not develop full immunity against diseases like malaria because the causative parasite, Plasmodium, exhibits significant antigenic variation. This means the parasite frequently changes its surface proteins, making it difficult for the immune system to recognize and mount a sustained, effective response against all forms of the parasite. The complex life cycle of the parasite also contributes to immune evasion.

Prevention is better than cure because it avoids the onset of disease, thereby preventing suffering, disability, and potential death. It also reduces healthcare costs, minimizes the spread of infectious diseases, and maintains overall public health and productivity, whereas a cure often involves costly and sometimes painful treatments after the damage has already occurred.