Reactivation of a Bacillus Calmette–Guérin Scar Following Routine Infant Vaccination

ABSTRACT

A 4‐month‐old infant developed erythema and induration at a Bacillus Calmette–Guérin (BCG) scar shortly after routine DTaP‐IPV‐Hib and pneumococcal vaccination. Laboratory findings were normal, and the lesion resolved spontaneously without treatment. This case highlights a rare, benign, self‐limited inflammatory reaction following routine childhood immunization.

Key Clinical Message

This is the first time that BCG vaccine reactivation has been reported after DTaP‐IPV‐Hib and conjugate pneumococcal vaccines.

1. Introduction

Bacillus Calmette–Guérin (BCG) scar reactivation is characterized by erythema, induration, swelling, or crusting at the site of a previous BCG inoculation. This finding has most commonly been associated with Kawasaki disease (KD) and has also been reported in multisystem inflammatory syndrome in children (MIS‐C), measles infection, influenza vaccination, tumor necrosis factor inhibitor therapy, and COVID‐19 vaccination [1, 2, 3, 4, 5]. The underlying mechanism remains unclear but is thought to involve immune‐mediated activation of local inflammatory pathways at the prior inoculation site. Although transient inflammatory reactions following vaccination are observed, reactivation of BCG scar following routine infant immunization has extremely rarely been reported.

2. Case Presentation

A 4‐month‐old boy presented with a 2‐day history of erythema and induration at the site of a previous BCG vaccination scar. He was born at term following an uncomplicated pregnancy and delivery and had no significant past medical history. Growth and developmental milestones were appropriate for age. The BCG vaccine had been administered at 1 month of age in the left deltoid region. A papule subsequently developed at the inoculation site and healed spontaneously, leaving a typical scar. Four days before presentation, the patient had received routine four‐month immunizations, including diphtheria, tetanus, acellular pertussis, inactivated poliovirus, and Haemophilus influenzae type b (DTaP‐IPV‐Hib), together with conjugated pneumococcal vaccines. There was no history of fever, respiratory symptoms, diarrhea, rash, recent infection, or trauma. No other adverse event following immunization (AEFI) was reported after this or previous vaccinations, and no local reaction was observed at the other injection sites.

Physical examination revealed a well‐appearing infant with normal vital signs. Well‐demarcated erythema and induration measuring approximately 10 × 12 mm were present at the BCG scar on the left deltoid region (Figure 1A). No ulceration, discharge, fluctuance, tenderness, conjunctivitis, oral mucosal involvement, cervical lymphadenopathy, edema of the extremities, or skin rash was observed.

FIGURE 1.

(A) Well‐defined erythema and induration at the site of the previous Bacillus Calmette–Guérin vaccination scar on the left deltoid region, observed 4 days after administration of DTaP‐IPV‐Hib and pneumococcal vaccines. (B) Nearly complete resolution of the lesion 3 weeks later without intervention.

Laboratory investigations demonstrated normal hemoglobin level, white blood cell count, platelet count, C‐reactive protein level, liver function tests, and urine microscopy. The lesion began to regress spontaneously on day 6 after onset and resolved completely within 3 weeks without treatment (Figure 1B). No desquamation, recurrence, or systemic symptoms developed during follow‐up and next vaccination.

3. Discussion

BCG scar reactivation is a well‐recognized finding in KD and has also been described in MIS‐C, viral infections such as measles, and following influenza and COVID‐19 vaccination [1, 2, 3, 4, 5]. Proposed mechanisms include nonspecific innate immune activation, cross‐reactivity between mycobacterial heat‐shock protein 65 and its human homologue, and locally enhanced cytokine responses (e.g., TNF‐α, IL‐6) [1, 2, 3, 4, 5]. Our patient received four non‐live, adjuvant‐containing vaccines simultaneously (DTaP‐IPV‐Hib and conjugated pneumococcal vaccine), precluding attribution to a single antigen; the absence of a live viral component favors a nonspecific, adjuvant‐ or cytokine‐driven local response, as proposed for influenza and inactivated COVID‐19 vaccines [4], rather than the antigenic cross‐reactivity postulated after live‐antigen exposures such as measles infection [5]. Unlike most previously reported cases, which occurred in the context of KD or MIS‐C with systemic febrile illness, our patient remained entirely well, with normal inflammatory markers and no mucocutaneous or cardiovascular findings, supporting a benign, vaccine‐related phenomenon. Vaccine manufacturer and lot numbers were not documented in the immunization record, a limitation shared with several prior reports.

To our knowledge, this is the first reported case of BCG scar reactivation following routine infant immunization with DTaP‐IPV‐Hib and conjugated pneumococcal vaccines. Awareness of this phenomenon may help clinicians avoid unnecessary investigations, antimicrobial therapy, and hospitalization.

4. Conclusion

Routine childhood immunization may rarely induce transient inflammatory reactivation at BCG inoculation sites. In otherwise healthy infants without systemic manifestations, this reaction appears to be benign and self‐limited.

Author Contributions

Fatih Demircioğlu: methodology, data curation, writing – review and editing, writing – original draft, conceptualization, investigation, formal analysis, supervision, visualization. Ayşe Sena Demircioğlu: data curation, methodology, investigation, visualization.

Funding

The authors have nothing to report.

Consent

Written informed consent was obtained from the patient's legal guardian for publication of this case report.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The authors have nothing to report.