Childhood BCG Vaccine May Continue to Protect Adults From TB

Laurie Barclay, MD

February 13, 2013

Bacillus Calmette–Guérin (BCG) vaccine has a protective effect against tuberculosis (TB) in adults decades after vaccination, according to a cross-sectional study. The observation, posted online September 27, 2012, and published in print February 11, 2013, in a special themed issue of Thorax coinciding with World TB Day, has important implications for national policy of BCG vaccination.

Several articles in the special issue note the resurgence of Mycobacterium tuberculosis as a highly successful pathogen with rising incidence rates.

"BCG vaccine has a documented protective effect against [TB] meningitis and disseminated TB in children, and is used as a complementary strategy for TB control," write Pei-Chun Chan, from the Third Division, Centers for Disease Control; the Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University; and the Department of Pediatrics, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, and colleagues. "Greater than 80% of neonates and infants are covered by BCG in countries where the vaccine is part of the national childhood immunisation programme."

"However," they add, "the protective effect of BCG against pulmonary TB in previous studies remains controversial."

Therefore, they designed the current study to determine whether the effect of BCG vaccination against TB infection lasts until adulthood. The investigators determined the prevalence of latent TB infection (LTBI) among HIV-negative men in a northern Taiwan prison holding more than 3000 men; the participants gave written informed consent before screening. The definition of LTBI was a QuantiFERON-TB Gold In-tube (QFT-IT; Cellestis) result of 0.35 IU/mL or more (≥0.7 IU/mL for recent LTBI). The investigators then studied the relationship between the number of BCG scars and LTBI stratified by age.

The overall prevalence of LTBI was 25% among the 2385 participants. With increasing age, the prevalence of LTBI increased, going from 14% at age 18 to 34 years to 32% at 35 to 54 years and to 50% at 55 years or older (P < .001 by the Cochran-Armitage Trend Test). For all LTBI and recent LTBI in all 3 age groups, the number of BCG scars was inversely correlated with QFT-IT result (P < .001 by Cochran-Mantel-Haenszel statistics).

Limitations of this study include its cross-sectional design, the use of the number of BCG scars as a proxy for BCG vaccination record, and a possible birth cohort effect.

"Our results suggest that BCG vaccine seems to have a protective effect in adults decades after vaccination according to the number of recent infections," the study authors write. "This finding has important implications for national policy of BCG vaccination. Further prospective cohort studies on the protective effect of BCG vaccination against TB infection in adults are warranted."

The Centers for Disease Control, Taiwan, supported this study. The study authors have disclosed no relevant financial relationships.

Thorax. 2013;68:263-268. Abstract