What Is the Significance of an Accelerated BCG Reaction in Children Living in Low Tuberculosis Incidence Countries?

In high tuberculosis (TB) incidence countries, accelerated Bacille Calmette-Guérin (BCG) reactions are considered markers of prior Mycobacterium tuberculosis exposure and may prompt investigation. Their significance in low-incidence countries is unclear. We aimed to describe the frequency, clinical characteristics and outcomes of accelerated BCG reactions in children vaccinated in Australia.

We conducted a retrospective case series at a quaternary hospital in Sydney, NSW. All children receiving intradermal Danish strain 1331 BCG between December 2023 and December 2024 were included. Accelerated reaction was defined as induration (≥ 0.5 cm) within 72 h, pustule formation within 5-7 days, or healing with scar formation at 10-15 days. Demographics, TB exposure risks, investigations and outcomes were collected.

Among 304 vaccinated children, 14 (5%) developed accelerated reactions. Median age was 3 years (IQR 6-45 months). Four had recently travelled to high-incidence countries; none had close contact with an individual with TB. Most reactions (12/14) occurred within 24-48 h. Six children underwent investigation due to epidemiological risk or young age; all results were negative. No child was diagnosed with M. tuberculosis infection or disease. All reactions resolved without antimycobacterial therapy.

In this single-centre cohort in a low TB incidence setting, accelerated BCG reactions occurred in one in 20 vaccinated children and were self-limiting. No association with M. tuberculosis infection was identified. These findings should be interpreted with caution and warrant confirmation in larger, multicentre studies. In the interim, a risk-based approach to investigation may be appropriate in low-incidence settings such as Australia.