Background The BCG vaccine's ability to prevent Mycobacterium tuberculosis infection (MTI) remains highly debated. In Greenland, BCG vaccination was introduced in 1955, but was temporarily discontinued (1991–1996) due to nationwide policy changes. The study aimed to use the transient stop in BCG vaccination to evaluate the effect of vaccination on MTI prevalence and TB incidence.

Methods MTI study: A cross-sectional study (2012), comprising East Greenlanders born during 1982–2006, evaluated the effect of BCG vaccination on MTI prevalence; a positive interferon γ release assay defined an MTI case. Associations were estimated using logistic regression. TB study: a cohort study covering the same birth cohorts with follow-up until 2012 evaluated the vaccine's effect on TB incidence. A personal identifier allowed for follow-up in the TB notification system. Associations were estimated using Cox regression.

Results MTI study: Included 953 participants; 81% were BCG-vaccinated; 29% had MTI, 23% among vaccinated and 57% among non-vaccinated. BCG vaccination reduced the odds of MTI, OR 0.52 (95% CI 0.32 to 0.85), p=0.01. Vaccine effectiveness against MTI was 20%. TB study: Included 1697 participants followed for 21 148 person-years. 6% were notified with TB, 4% among vaccinated and 11% among non-vaccinated. BCG vaccination reduced the risk of TB, HR 0.50 (95% CI 0.26 to 0.95), p=0.03, yielding a vaccine effectiveness of 50%.

Conclusions BCG vaccination was effective in reducing both MTI and TB disease among children and young adults in a TB high-endemic setting in Greenland.