Elsevier

Vaccine

Volume 26, Issue 18, 24 April 2008, Pages 2253-2259
Vaccine

Assessing the impact of different BCG vaccination strategies on severe childhood TB in low-intermediate prevalence settings

https://doi.org/10.1016/j.vaccine.2008.02.038Get rights and content

Summary

The decrease in overall incidence of TB in industrialised countries, together with the increasing concern for adverse events following BCG immunization, has led to important modifications of BCG policies in the last decades. This article adapts and validates – with surveillance data – a theoretical model estimating the impact of different national BCG vaccination policies on severe childhood TB in low to intermediate TB prevalent countries. The model shows that a universal BCG programme could be beneficial in settings with prevalence levels around 30 sputum smear positive per 100,000. In settings with prevalence levels below 15 per 100,000 the benefit of universal BCG vaccination should be carefully assessed, particularly where prevalence is below 5 per 100,000 and universal vaccination might lead to an excess of adverse events per case prevented. To this purpose the model also provides a tool to assess the theoretical impact of a policy change towards selective ‘high-risk groups’ vaccination.

Introduction

The Bacillus Calmette-Guérin (BCG) vaccine is one of the most widely used of all current vaccines [1].

Whilst BCG efficacy against pulmonary TB – particularly in adults – is highly variable, more consistent results are available on BCG efficacy against tuberculous meningitis and miliary tuberculosis (severe forms of TB) [2], [3].

BCG vaccination often results in local adverse effects, but serious complications are rare. Globally, incidence of fatal adverse events has been rarely reported, ranging from 0.01 to 43.4 cases per million vaccines. Such severe adverse events usually occur in infants with impaired immunity [4].

In Western Europe the most frequently reported adverse event is suppurative lymphadenitis; osteitis and occasionally disseminated BCG infection have also been reported [5], [6].

The decrease in overall incidence of TB in industrialised countries, together with the increasing concern for adverse events following immunization (AEFI), has led to important modifications of BCG policies in the last decades [7], [8]. BCG vaccination has been discontinued or has been limited to children ‘at risk’ in a growing number of countries in the European Union (EU) [9]. Policy changes are currently under discussion in other EU countries.

Decision on discontinuing universal BCG vaccination should rest upon a cost–benefit analysis taking into account several variables, namely the expected number of severe TB cases in children, the expected number of AEFI, and the number needed to vaccinate per severe TB case prevented.

We provide a theoretical model to assess cost–benefit of different options of BCG vaccination strategies in low to intermediate TB burden countries with respect to prevention of severe TB cases in childhood.

Section snippets

Methods

We aimed at adapting a model that would allow us to estimate the effects of withdrawal or change in BCG vaccination strategy in low to intermediate TB prevalence settings.

Results

Main outcomes of the modelapplied to the 5 settings are showed in Table 1.

TB prevalence (SS + per 100,000 population) ranges from 1.7 (setting A, 5th percentile) to 33.4 (setting E, 95th percentile), corresponding to ARI values ranging from 0.01 to 0.20 per 100,000 population.

The number of prevented severe TB cases in the hypothetical 100,000 children birth cohort (100% vaccine coverage, 80% vaccine efficacy) ranges from 0.6 to 12.0, with a NNV ranging from 161,499 to 8317. The expected number of

Discussion

The purpose of our work was to adapt a model that would estimate the effects of withdrawal or change in BCG vaccination under different settings. We did not specifically address the issue of deriving ARI from prevalence of disease but we merely applied previously developed methodologies. We recognize that prevalence estimates carry a degree of uncertainty. Furthermore, calculations were made on the basis of smear positive prevalence only, disregarding the possible transmission from smear

Conclusion

In our work we aimed at providing a tool to facilitate assessment of BCG policies in low to intermediate burden settings.

The theoretical model we discussed is particularly relevant to the European countries where smear positive TB prevalence ranges from 1 to 88 per 100,000. According to the model, in European countries, where the prevalence level is under 5 per 100,000, it appears that universal vaccination might lead to an excess of adverse events per severe TB case prevented. In countries

Acknowledgments

The authors would like to thank Dr. Victoria Romanus and Dr. Bernadette Bourdin-Trunz for commenting and providing valuable suggestions on the early draft of the work.

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