The most common causes of vaccine compromise include failures related to the host, the vaccine itself, the pathogen, and errors in storage, handling, and administration. Host-related causes include immunocompromise due to medical conditions (e.g., diabetes, HIV, cancers), immunosenescence (weaker immune response in infants and the elderly), obesity, genetics, and medications that impair immune response. Immunocompromised individuals may have insufficient or absent immune responses to vaccines. Vaccine-related causes are often improper storage (e.g., exposure to freezing or temperatures above recommended range) and handling, which can reduce vaccine effectiveness. Improper administration (wrong injection method or site, incorrect dosing) also compromises vaccine efficacy. Pathogen factors like antigenic drift (mutations in virus strains) can cause vaccines to be less effective if circulating strains differ significantly from the vaccine strains. Additional causes include study design factors affecting perceived vaccine effectiveness and apparent but false vaccine failures, where vaccines do not cover emergent or mismatched strains. In summary, vaccine compromise is commonly due to immunocompromised hosts, improper vaccine storage or administration, and mismatch between vaccine and circulating pathogens.