Avidity refers to the overall strength of the binding interaction between an antibody and its antigen. It is a measure of how tightly an antibody can bind to multiple sites on an antigen, which can enhance the effectiveness of the immune response. Avidity is influenced by factors such as the affinity of the antibody for each binding site and the number of binding sites available on the antigen. In immunology, avidity is important for understanding how well the immune system can recognize and respond to pathogens. High avidity interactions can lead to more effective neutralization of viruses or bacteria, making it a key concept in vaccine development and therapeutic antibody design, particularly in relation to diseases like COVID-19.