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

## TL;DR

A man's BCG vaccination scar became inflamed after an influenza shot nearby, suggesting a possible immune interaction between the two vaccines.

## Contribution

This case report highlights a potential immunological link between BCG and influenza vaccines based on a localized reaction.

## Key findings

- A BCG scar showed erythema two days after an influenza vaccination nearby.
- BCG vaccination may enhance TNF-α and IL-6 production following influenza vaccination.
- BCG-vaccinated individuals may have stronger and faster antibody responses to influenza vaccines.

## Abstract

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.