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Protective effect of BCG vaccination in a nursery outbreak in 2009: time to reconsider the vaccination threshold?
J Eriksen1, J Y Chow, V Mellis
1European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden. jaran.eriksen@ki.se
Insights
BCG vaccination significantly protected children against tuberculosis infection during a London nursery outbreak. This suggests widespread BCG immunization could prevent many Mycobacterium tuberculosis infections in young children.
Area of Science:
- Public Health
- Infectious Disease Epidemiology
- Vaccinology
Background:
- A tuberculosis (TB) outbreak occurred in a London nursery involving a smear-positive pulmonary TB case in a nursery teacher.
- The index case had been symptomatic for 9 months while working, indicating potential for significant transmission.
- The study aimed to assess the protective effect of Bacillus Calmette-Guérin (BCG) vaccination against latent Mycobacterium tuberculosis infection.
Purpose of the Study:
- To describe a tuberculosis outbreak in a nursery setting.
- To evaluate the effectiveness of BCG vaccination in preventing latent Mycobacterium tuberculosis infection.
- To identify risk factors associated with TB transmission in young children.
Main Methods:
- Screening involved chest X-ray and interferon-gamma release assay (IGRA) for nursery children, staff, and contacts.
- A 'stone-in-the-pond' approach was used for contact tracing and screening.
- Multivariable logistic regression analysis was employed to assess factors including BCG vaccination status.
Main Results:
- 12 active TB cases and 43 latent TB cases (72% children) were identified among 168 children, 31 staff, and 57 contacts.
- BCG vaccination showed a significant protective effect against M. tuberculosis infection in children (OR 0.25).
- Being taught by the index case was strongly associated with acquiring TB infection (OR 18.91), with an estimated vaccine effectiveness of 66%.
Conclusions:
- The nursery outbreak demonstrated extensive transmission of tuberculosis, particularly among very young children.
- BCG vaccination appears to provide a protective effect against TB infection, as indicated by positive IGRA results in this cohort.
- The findings support the role of BCG vaccination in preventing TB infection in high-risk pediatric settings.
Background:
In July 2008 a case of smear-positive pulmonary tuberculosis (TB) in a white UK-born nursery teacher was notified in London. The case had been symptomatic for 9 months while working in the nursery. The outbreak is described and the protective effect of BCG vaccination against latent Mycobacterium tuberculosis infection as measured by an interferon gamma release assay (IGRA) is assessed.
Methods:
Screening by chest X-ray and IGRA of nursery children, staff and their contacts was conducted using a 'stone-in-the pond' approach. Information was collected on various factors including BCG vaccination status, and data were analysed using multivariable logistic regression.
Results:
Overall, 168 children, 31 staff members and 57 other adults associated with the nursery were screened for TB. There were 12 cases of active TB and 43 cases of latent TB (72% children). 37.5% (95% CI 18% to 56%) and 40% (95% CI 30% to 50%) had a positive IGRA among teachers and children, respectively. 42% of children and 60% of adults were BCG vaccinated. In the adjusted analysis, BCG vaccination showed a significant protective effect against M tuberculosis infection in children (OR 0.25, 95% CI 0.09 to 0.69) and being taught by the index case was associated with acquiring TB infection (OR 18.91, 95% CI 4.43 to 80.79). A vaccine effectiveness of 66% was calculated, implying that 21 of the 32 infections could have been avoided if all children had been vaccinated with BCG.
Conclusions:
This outbreak shows extensive transmission of TB among very young children. BCG seems to have a protective effect against TB infection as assessed by positive IGRA in this cohort.
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