Reactivation of BCG vaccination SCAR after influenza vaccination: a case report.

The Bacillus Calmette-Guerin (BCG) vaccine, a live attenuated vaccine derived from Mycobacterium bovis, is widely used for tuberculosis prevention and has been linked to various immunological responses beyond its intended purpose. A 23-years-old healthy and allergy-free man was vaccinated for the current year's influenza on his left arm. Two days after inoculation, the patient's BCG scar on his left arm was erythematous, while the influenza vaccination site (located 3 cm from the BCG scar) remained unchanged. A possible ipsilateral relationship between the BCG scar and the influenza vaccine site is suggested. BCG vaccination influences the increase in TNF-α and IL-6 production following influenza vaccination. In BCG-vaccinated subjects, hemagglutinin-inhibition antibody responses against the A(H1N1)pdm09 vaccine strain is markedly enhanced, with a trend toward more-rapid seroconversion. Understanding this BCG and influenza vaccines interaction is crucial for healthcare providers to differentiate between benign post-vaccination reactions and those that may require further clinical evaluation.