Vaccine lot numbers are critical identifiers used to track batches of vaccines throughout their lifecycle, from production to administration. These unique codes, assigned by manufacturers, enable traceability for safety monitoring, quality control, and recalls. In the U.S., lot numbers are recorded in the Vaccine Adverse Event Reporting System (VAERS), while globally, they are overseen by national regulatory authorities and the World Health Organization (WHO). This article explores how vaccine lot numbers are composed, the character rules they follow, and whether ambiguous characters like “O” or “l” are avoided to prevent confusion with “0” or “1.” What Are Vaccine Lot Numbers? A vaccine lot number is a unique identifier assigned to a specific batch of vaccines produced under identical conditions, such as during a single manufacturing run or at…