Booster injection, also known as a booster shot or a booster dose, is a type of vaccination that is designed to enhance or extend the protection provided by an initial vaccination. It typically involves the administration of a smaller dose of the same vaccine to stimulate the immune system and maintain immunity against a particular pathogen. Synonyms for booster injection include reinforcing vaccine, supplementary immunization, additional shot, and follow-up vaccine. Other related terms include vaccine boost, vaccine extension, vaccine refill, and vaccine top-up. Regardless of the terminology used, booster injections play a critical role in preventing the spread of infectious diseases and protecting public health.