Retrospective cohort study exploring the impact of universal Tuberculosis (TB) vaccination cessation on the epidemiology of paediatric TB in Ireland, 2011-2021.

BACKGROUND:Since 2010, Ireland's Tuberculosis (TB) crude incidence rate (CIR) remains below 10 per 100,000 population defining it as a low TB incidence country. Ireland maintained a universal BCG vaccination programme until its discontinuation in 2015 due to lack of vaccine supply. This study explores the impact of discontinuing a national universal BCG vaccination programme on the epidemiology of paediatric TB cases. METHODS:We retrospectively analysed TB notifications aged 0-6 years old reported to the Irish National TB Surveillance System between 2011 and 2021. Key epidemiological characteristics and temporal trends in TB age specific incidence rates (ASIRs) were compared between 0 and 6 year old cases born during a period of universal BCG vaccination (2007-2015) and 0-6 year old cases born after BCG vaccination ceased (2015-2021). RESULTS:No significant temporal trend was detected in the overall 0-6 year old ASIR by notification year during 2011-2021 (IRR:0.95; 0.86-1.1). However, the temporal trend for cases born during universal vaccination showed a significant decline (0.74; CIR: 0.62-0.89) while cases born after BCG vaccination ceased had a non-significant increase (1.2; CIR: 0.73-1.86). A significantly declining temporal trend was detected among cases born in Ireland during universal vaccination (IRR:0.73; 0.62-0.86), but no significant trend was detected in the cases born outside Ireland during universal vaccination (IRR:0.83; 0.53-1.31). No significant trend was detected in cases born after vaccination ceased in either cases born in Ireland (IRR:1.0; 0.60-1.65) or those born outside Ireland (IRR:0.64; 0.29-1.40). CONCLUSIONS:Universal BCG cessation has not yet directly impacted on TB cases among 0-6 year olds in Ireland. However, interruption of the previously declining temporal trend in this cohort during universal vaccination may be an early warning of a future increase. Paediatric TB cases remain an important cohort for timely surveillance to monitor trends in this primarily unvaccinated cohort to evaluate the long-term effects.