Introduction
The Bacille Calmette-Guérin (BCG) vaccine, as the only available vaccine against Mycobacterium Tuberculosis, is recommended by the World Health Organization (WHO) in numerous countries (1, 2). According to the expanded program of immunization (EPI) in Iran, all children receive BCG vaccination at birth. BCG is derived from live attenuated Mycobacterium Bovis and there are possible local, regional or systemic complications following the vaccine injection (2, 3). The strain of the BCG vaccine, the child’s immune response, and injection technique especially dosage and administration route are considerable factors for the development of the possible complications (4, 5). Mycobacterial infection is the most common culprit for cold abscess, known as an abscess without severe inflammation. The abscess also can be a result of incorrect intramuscular BCG vaccine injection (6, 7). Here, we report three cases of BCG-induced cold abscess as a result of erroneous injection of vaccine into the infant’s thigh muscle.