A case-control study of BCG and childhood tuberculosis in Cali, Colombia

Effectiveness of BCG Vaccination Against Mycobacterium tuberculosis Infection in Adults: A Cross-sectional Analysis of a UK-Based Cohort

BACKGROUND

BCG appears to reduce acquisition of Mycobacterium tuberculosis infection in children, measured using interferon-gamma release assays (IGRAs). We explored whether BCG vaccination continues to be associated with decreased prevalence of M. tuberculosis infection in adults.

METHODS

We conducted a cross-sectional analysis of data from adult contacts of tuberculosis cases participating in a UK cohort study. Vaccine effectiveness (VE) of BCG, ascertained based on presence of a scar or vaccination history, against latent tuberculosis infection (LTBI), measured via IGRA, was assessed using multivariable logistic regression. The effects of age at BCG and time since vaccination were also explored.

RESULTS

Of 3453 recent tuberculosis contacts, 27.5% had LTBI. There was strong evidence of an association between BCG and LTBI (adjusted odds ratio = 0.70; 95% confidence interval, .56-.87; P = .0017) yielding a VE of 30%. VE declined with time since vaccination but there was evidence that LTBI prevalence was lower amongst vaccinated individuals even >20 years after vaccination, compared with nonvaccinated participants.

CONCLUSIONS

BCG is associated with lower prevalence of LTBI in adult contacts of tuberculosis. These results contribute to growing evidence that suggests BCG may protect against M. tuberculosis infection as well as disease. This has implications for immunization programs, vaccine development, and tuberculosis control efforts worldwide.

CLINICAL TRIALS REGISTRATION

NCT01162265.

Comparable CD4 and CD8 T cell responses and cytokine release after at-birth and delayed BCG immunisation in infants born in Australia

BACKGROUND

More than 120 million doses of BCG vaccine are administered worldwide each year. Most infants are given BCG at birth in accordance with WHO recommendations. However, the effect of the maturing neonatal immune system on the immune response and protection conferred by BCG remains uncertain. Previous studies investigating the influence of age at immunisation on the immune response induced by BCG have reported conflicting results. This study compared BCG given at birth and at two months of age in infants in Australia.

METHODS

Infants born in Melbourne were randomly allocated to immunisation with BCG-Denmark at birth or two months of age. Ten weeks after immunisation, anti-mycobacterial immune responses were measured in a whole blood assay using intracellular cytokine assays and xMAP multiplex cytokine analysis.

RESULTS

Result from 98 BCG-immunised infants were included in the final analysis. BCG immunisation at birth (n=54) and at 2months of age (n=44) induced comparable proportions of mycobacteria-specific cytokine-producing CD4 and CD8 T cells, as well as comparable proportions of polyfunctional (TNF(+) IL-2(+) IFN-γ(+)) CD4 T cells. Concentrations of cytokines in supernatants were also similar in both groups.

CONCLUSIONS

Cellular immunity measured 10weeks after BCG immunisation was similar in infants given BCG at birth and in those given BCG at 2months of age. Although definitive correlates of protection against TB remain uncertain, these results suggest that delaying BCG immunisation does not confer any immunological advantage in cellular immunity.

Effectiveness of the First Dose of BCG against Tuberculosis among HIV-Infected, Predominantly Immunodeficient Children

The objective of this study was to estimate the protective effect of Bacille Calmette-Guérin (BCG) vaccine against tuberculosis among (predominantly immunodeficient) HIV-infected children in Angola. A hospital-based case-control study was conducted with 230 cases, children coinfected with tuberculosis, and 672 controls, HIV-infected children from the same hospital, aged 18 months to 13 years. The presence of a vaccination scar was taken as a proxy marker for BCG vaccination. The crude effectiveness was 8% (95% CI: -26 to 32) and the adjusted effectiveness was 30% (95% CI: -75 to 72). The present study suggests that BCG does not have a protective effect against tuberculosis among immunodeficient HIV-infected children. Since BCG is no longer given to HIV-infected children, the study may not be replicated. Accepting that these findings should be considered with caution, they are nonetheless likely to be the last estimate of BCG efficacy in a sufficiently powered study.

The BCG controversy

The history of tuberculosis control by vaccination with Bacille Calmette-Guérin (BCG) is reviewed. Use of the vaccine is evaluated in light of conflicting results from trials of BCG efficacy. Explanatinations are suggested for the variations between trials, and the continued use of BCG as a vaccine against tuberculosis is discussed.

Comparative tuberculosis (TB) prevention effectiveness in children of Bacillus Calmette-Guérin (BCG) vaccines from different sources, Kazakhstan

BACKGROUND

Except during a 1-year period when BCG vaccine was not routinely administered, annual coverage of infants with Bacillus Calmette-Guérin (BCG) in Kazakhstan since 2002 has exceeded 95%. BCG preparations from different sources (Japan, Serbia, and Russia) or none were used exclusively in comparable 7-month time-frames, September through March, in 4 successive years beginning in 2002. Our objective was to assess relative effectiveness of BCG immunization.

METHODS/FINDINGS

We compared outcomes of birth cohorts from the 4 time-frames retrospectively. Three cohorts received vaccine from one of three manufacturers exclusively, and one cohort was not vaccinated. Cohorts were followed for 3 years for notifications of clinical TB and of culture-confirmed TB, and for 21 months for TB meningitis notifications. Prevention effectiveness based on relative risk of TB incidence was calculated for each vaccinated cohort compared to the non-vaccinated cohort. Although there were differences in prevention effectiveness observed among the three BCG vaccines, all were protective. The Japanese vaccine (currently used in Kazakhstan), the Serbian vaccine, and the Russian vaccine respectively were 69%, 43%, and 22% effective with respect to clinical TB notifications, and 92%, 82%, and 51% effective with respect to culture confirmed TB. All three vaccines were >70% effective with respect to TB meningitis.

LIMITATIONS

Potential limitations included considerations that 1) the methodology used was retrospective, 2) multiple risk factors could have varied between cohorts and affected prevention effectiveness measures, 3) most cases were clinically diagnosed, and TB culture-positive case numbers and TB meningitis case numbers were sparse, and 4) small variations in reported population TB burden could have affected relative risk of exposure for cohorts.

CONCLUSIONS/SIGNIFICANCE

All three BCG vaccines evaluated were protective against TB, and prevention effectiveness varied by manufacturer. When setting national immunization policy, consideration should be given to prevention effectiveness of BCG preparations.

To BCG or not to BCG? Preventing travel-associated tuberculosis in children

With the rise in travel to countries with a high prevalence of tuberculosis (TB), the risk of travel-associated TB is of increasing concern. However, the use of Bacille Calmette-Guérin (BCG) vaccine for the prevention of travel-associated TB is a neglected area. We review and discuss national and international recommendations and guidelines for the prevention of travel-associated TB in children. Three children who developed travel-associated TB disease are described to illustrate that current recommendations, and in particular the use of pre-travel BCG immunisation, are inconsistent and controversial. The wide variation in recommendations reflects the paucity of data on the effectiveness of BCG immunisation and other preventive strategies in this setting. Until evidence-based guidelines can be produced, we believe that a low threshold for recommending BCG immunisation for travelling children is the safest strategy. A practical approach to deciding which children should be immunised with BCG prior to travel is presented.

Vaccination strategies to prevent tuberculosis in the new millennium: from BCG to new vaccine candidates

Current global control efforts targeting tuberculosis (TB) include the treatment of latent TB infection, case detection and treatment with directly observed therapy short-course (DOTS), and BCG (bacille Calmette-Guérin) vaccination. However, BCG has been found to decrease only childhood TB morbidity and mortality but has a very limited effect in the transmission dynamics of the infection. These limitations of BCG are the driving force for the development of new TB vaccines. New TB vaccine candidates have entered clinical evaluation and many more are in the pipeline to undergo clinical testing. New vaccine candidates may offer better protection than that afforded by currently available BCG vaccines. Furthermore, combined vaccination schedules against TB seem to be a promising strategy in the new millennium.

The utility and interpretation of tuberculin skin tests in the Middle East

Tuberculin skin test (TST) interpretation can be confounded by Bacillus Calmette-Guerin (BCG) vaccination and infection with nontuberculosis mycobacteria (NTM). However, a wealth of epidemiologic information has allowed the formulation of recommendations for reasonably informed interpretation of the TST in most clinical situations. In the Middle East, the TST remains a useful test. BCG vaccination is given at birth, which should have minimal effect on TST reactions in adolescents or adults. In countries of the Middle East with moderate to high incidence of active smear-positive pulmonary TB (>20 per 100,000 per year), a positive TST will almost always indicate true TB infection. However, in Middle East countries with very low incidence of active TB (<10 per 100,000 per year), a positive TST will more likely be false positive because BCG vaccination is still routinely given; until BCG vaccination is abandoned, the TST will be less useful in these countries. These findings are applicable to countries in other regions of the world, and the utility TST will also be increased where the likelihood of TB infection is higher and lowered where TB infection is unlikely, yet BCG vaccination is still given.

BCG--different strains, different vaccines?

After nearly a century of use, BCG vaccines continue to generate controversy and confusion. Their ability to prevent tuberculosis in studies has been inconsistent. When they have been protective, no clear mechanism of action has been established. Furthermore, the existence of different BCG strains has been described since the 1940s. These strains vary according to several laboratory properties, which may or may not translate into a discernible effect on vaccination. With recent genomic comparisons, it is now clear that different BCG vaccine strains have evolved and differ from each other and from the original BCG first used in 1921. Some of these genetic alterations explain certain variations in laboratory properties of BCG. However, these mutations in BCG strains have yet to be shown to affect BCG-associated protection and/or adverse effects. Continuing research is attempting to assess the effect of these genetic alterations on properties of BCG strains, with the goals of suggesting the ideal BCG for vaccination and providing avenues for improvement on existing BCG vaccines.

BCG vaccine effectiveness in preventing tuberculosis and its interaction with human immunodeficiency virus infection

BACKGROUND

To explore Bacillus Calmette-Guérin vaccine (BCG) as a protective factor against tuberculosis (TB) and how human immunodeficiency virus (HIV) infection modifies the effect of BCG on TB.

METHODS

Two matched case-control studies were conducted. One study compared TB cases and controls who were HIV positive. The second compared TB cases and controls who were HIV negative. The study population consisted of 88 TB cases and 88 controls among HIV-positive individuals and 314 TB cases and 310 controls among HIV-negative individuals. Cases were new TB diagnoses, confirmed by either bacteriology, pathology, radiology or clinical response to treatment; controls were selected from people without TB symptoms and who sought medical attention in the same institution where a case was enrolled. BCG was assessed by the presence of a typical scar.

RESULTS

The level of protection against all clinical forms of TB was 22% among HIV positive individuals (odds ratio [OR] = 0.78, 95% CI : 0.48-1.26) and 26% among HIV negatives (OR = 0.74, 95% CI : 0.52-1.05). There was a significant difference (P = 0.002) in the level of protection against extrapulmonary TB (ETB) between HIV-negative (OR = 0.54, 95% CI : 0.32-0.93) and HIV-positive individuals (OR = 1.36, 95% CI : 0.72-2.57).

CONCLUSION

BCG has a modest protective effect against all forms of TB independent of HIV status, and BCG confers protection against extrapulmonary TB among HIV-negative individuals. However, HIV infection seems to abrogate the protective effect of BCG against extrapulmonary TB. Our data support the public health importance of BCG vaccine in the prevention of extrapulmonary TB among immunocompetent individuals.

Preventing tuberculosis with bacillus Calmette-Guérin vaccine: a meta-analysis of the literature

This article reviews a previously published meta-analysis of 1264 titles or abstracts and 70 selected studies for evaluation of the efficacy of bacillus Calmette-Guérin (BCG) vaccine in preventing tuberculosis. Following review, data from 26 studies were included in the analysis. These 26 studies reveal that vaccination with BCG significantly reduces the risk of tuberculosis by an average of 50%. This level of protection persists across a number of subgroups defined by age at vaccination and study design. Vaccination with BCG was significantly associated with a reduction in the incidence of pulmonary tuberculosis and extrapulmonary disease. In general, the results of this meta-analysis lend weight and confidence to arguments favoring the use of BCG vaccine.

Tuberculosis Risk and Prevention in Travelers-What about BCG?

Tuberculosis (TB) is one of the most important health problems in many tropical and developing countries, particularly since the advent of the human immuno- deficiency virus (HIV) epidemic. The level of TB transmission is much greater in these countries than in most of western Europe or North America. For example, the annual risk of infection with Mycobacterium tuberculosis is estimated to be 300 times higher in some subSaharan African countries1 than in the Netherlands.2 Travel guidelines and advice vary widely in the emphasis placed on TB and on specific recommendations for prevention. American sources generally advise that use of the bacille Calmette-Guérin (BCG) vaccine in travelers be limited to exceptional circumstances3 while some European authorities advocate broader use.4-6 This article reviews the risk of TB in travelers and possible approaches to its prevention, including the use of BCG vaccination.

Effectiveness of mass neonatal BCG vaccination in the prevention of pulmonary tuberculosis: a case-control study in Nagpur, India

SETTING

Government Medical College, Nagpur, India, a tertiary care hospital.

OBJECTIVE

To estimate the effectiveness of mass neonatal BCG vaccination in the prevention of pulmonary tuberculosis in Nagpur, India.

DESIGN

A hospital-based pair-matched case-control study with a case of 1:3, including 144 cases of pulmonary tuberculosis and 432 controls.

RESULTS

The overall vaccine effectiveness estimated in the present study was 60% (95% Confidence Interval [CI] 43%-72%). The protective effect was more in males in the age group 21-30 years. The prevented fraction was 39% (95% CI 24%-52%).

CONCLUSION

The moderate effectiveness demonstrated in this study needs to be substantiated for other forms of tuberculosis by undertaking community-based case-control studies, before attempting to justify the use of mass neonatal BCG vaccination strategy as a part of the national programme.

Field trials of tuberculosis vaccines: how could we have done them better?

Nineteen controlled trials of vaccination against tuberculosis are reviewed. Most involved very large numbers of participants and represented a wide variety of geographic and socioeconomic conditions. The trials were conducted under field conditions that sometimes verged on the primitive. Length of follow-up for tuberculosis ranged from 3 to 23 years, and up to 28 years for cancer. Under these circumstances, compromises and mistakes were made along with notable successes. With the current interest in the immunology of tuberculosis and other chronic infectious diseases giving rise to renewed hope for more efficacious vaccines, lessons from the past can be useful in planning the long-term evaluations that will be needed as these hoped-for vaccines become available.

A re-examination of the variations in the efficacy of BCG vaccination against tuberculosis in clinical trials

SETTING

The findings of the principal controlled trials of BCG vaccination against tuberculosis are reviewed.

OBJECTIVE

To investigate possible reasons for the wide variations in vaccine efficacy in different trials, and in particular for the apparent adverse effect in the first few years in the trial in Chingleput, South India.

OBSERVATIONS

(1) A substantial reduction, or even a reversal, of overall efficacy could result if the assessment of vaccine efficacy included a subgroup adversely affected by vaccination. (2) Several trials include in the assessment many subjects with weak initial tuberculin sensitivity, due either to environmental mycobacterial infection or to Mycobacterium tuberculosis infection. It is accepted that vaccine efficacy may be moderately reduced in the former subgroup. It is postulated that the latter subgroup may be at risk of reactivation of tuberculosis soon after vaccination, perhaps from focal reactions due to enhancement of their weak sensitivity. (3) The low levels of efficacy in several trials, and the early adverse effect in Chingleput, are broadly consistent with this hypothesis.

CONCLUSION

Clinical tuberculosis due to BCG vaccination of subjects with weak tuberculin sensitivity following M. tuberculosis infection may make an important contribution to the variations in efficacy found in clinical trials.

Immunology of tuberculosis

TB is a chronic, necrotizing infection caused by M. tuberculosis. The clinical manifestations of disease are the result of a balance between the host response and bacterial virulence. Cellular immunity is responsible for effective control of infection, but cytokines released during the process of cellular immunity may also cause harm to the host. Humoral immunity plays little part in protection against TB. Individuals with defective cellular immunity are much more susceptible to disease from M. tuberculosis and are more likely to have a disseminated form of TB.

Retrospective evaluation of the efficacy of the BCG vaccination campaign of newborns in Barcelona, Spain

The efficacy of the BCG vaccination campaign of neonates in Barcelona, carried out in the period 1966-1974, was evaluated with a study of cases and controls made during the period 1978-1988 in patients between the ages of 4 and 21 years. It shows that the efficacy of this vaccination campaign was 32%, that it was greater in men than women and that it decreased with the passage of time. The number of cases of tuberculosis prevented by this campaign is calculated at 13.4%. Given that the vaccine used offered maximum guarantees, the authors consider that this poor efficacy must be attributed to operational deficiencies in the vaccination campaign itself.

Use of BCG vaccine in shelters for the homeless. A decision analysis

As a result of many interacting variables, including crowded shelters and limited access to health care, homeless persons are at high risk for tuberculosis. Using traditional approaches, control of tuberculosis in this population has been difficult. Decision analysis was used to investigate the cost-effectiveness of BCG (bacillus Calmette-Guérin) vaccination in persons attending homeless shelters. This vaccination was cost-effective over a wide range of assumptions. Using conservative assumptions, a vaccine that was at least 40 percent effective would result in a net cost savings. If the efficacy of the vaccine were 50 percent, $4,000 would be saved, 12 life-years gained, and 23 cases of active tuberculosis prevented for every 1,000 persons vaccinated. Further study of the BCG vaccine in homeless persons and other populations at risk is warranted.

Tuberculosis: commentary on a reemergent killer

Tuberculosis remains the leading cause of death in the world from a single infectious disease, although there is little knowledge of the mechanisms of its pathogenesis and protection from it. After a century of decline in the United States, tuberculosis is increasing, and strains resistant to multiple antibiotics have emerged. This excess of cases is attributable to changes in the social structure in cities, the human immunodeficiency virus epidemic, and a failure in certain major cities to improve public treatment programs. The economic costs of not adequately addressing the problem of tuberculosis in this country are estimated from an epidemiological model.

Protective efficacy of BCG against leprosy in Northern Malawi

The effectiveness of a BCG vaccination programme in protecting against leprosy was assessed by case-control and cohort analyses of data from the Lepra Evaluation Project in Karonga District, Northern Malawi. Results indicate that BCG provides at least 50% protection against leprosy in this population and that protection is independent of age, sex, schooling status, or location within the project area. Agreement between these findings and those from a controlled trial in Uganda indicates that BCG is sufficiently effective against leprosy in East and Central Africa to be considered an important element of leprosy control in that region.