Every year, 1.5 million people die from tuberculosis, and in South Africa, 1% of the population develops active TB annually. The problem is that most TB arises from dormant infections—latent TB—acquired in childhood, which reactivates later in life. Current TB control focuses on treating active cases, but this won’t eliminate TB in high-burden countries because new cases keep emerging from the vast pool of people with latent infections. The existing BCG vaccine offers little protection in Africa, and a recent vaccine trial disappointed. This trial tests a simple, cheap intervention: weekly vitamin D supplements for 5,400 schoolchildren in Cape Town townships, where 88% of people have low vitamin D levels. Vitamin D boosts white blood cells’ ability to kill TB bacteria, and a small Mongolian study found it cut latent TB risk by 59%. If this larger trial confirms that, vitamin D could become a safe, low-cost tool to prevent children from acquiring latent TB in the first place. That would give TB control programmes a new strategy to reduce the reservoir of future active cases, potentially helping meet the WHO’s 2050 elimination target. Two billion people worldwide have latent TB, and 1 billion are vitamin D deficient, so the global impact could be substantial.
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1) Context of the research Tuberculosis (TB) kills 1.5 million people each year. South Africa has one of the TB rates in the world: 1% of the population develops TB each year. The World Health Organisation aims to eliminate TB by 2050. TB usually arises when a dormant infection with TB bacteria, termed 'latent TB infection' (LTBI) becomes active. LTBI is usually acquired in childhood following inhalation of TB bacteria coughed up by a person with infectious active TB. By the time they reach adulthood, approximately 80% of people in South Africa will have acquired LTBI. In 10-20% of these people, LTBI will reactivate to cause active TB disease in their lifetime. Preventing people - especially children - from acquiring LTBI in the first place could therefore reduce the number of people who go on to develop active TB. Currently, however, conventional approaches to TB control focus instead on finding and treating people with infectious active TB in order to break the cycle of transmission. This strategy will not eliminate TB in countries where it is very common because new cases of active TB will continue to arise from the many people who have LTBI. The existing TB vaccine, BCG, has been shown to offer very limited protection against TB in Africa - if any - and a recent trial of a new vaccine had disappointing results. New strategies to protect children from acquiring LTBI will therefore be needed if the 2050 elimination target is to be met. We propose that supplementation with vitamin D - the sunshine vitamin - could boost immunity to TB bacteria, and thereby prevent LTBI in children exposed to infectious TB. Vitamin D has long been recognised to boost immunity to TB bacteria. Before the discovery of antibiotics, cod liver oil (rich in vitamin D) and sunbathing (which boosts vitamin D levels) were both used to treat TB. Laboratory experiments show that vitamin D helps white blood cells to kill TB bacteria. Studies in patients show that those with lower vitamin D levels are more susceptible to acquiring LTBI after exposure to an infectious TB case. Moreover, a recent clinical trial in 120 schoolchildren in Mongolia showed that vitamin D supplementation reduced risk of acquiring LTBI by 59%. Although promising, this study was small, and a much larger trial is needed before vitamin D can be recommended for TB prevention. 2) Aims and objectives The primary aim of this research is to determine whether a weekly vitamin D supplement, taken by mouth for 3 years, can reduce the risk of acquiring LTBI among schoolchildren in an area where TB is very common. We will achieve this by conducting a clinical trial in 5,400 primary schoolchildren in townships around Cape Town, where we have previously shown that 88% of people have low vitamin D levels. Participants will have a blood test for LTBI at baseline: those who test negative will be allocated to receive weekly doses of vitamin D or placebo (dummy medication with identical taste and appearance) at random. Study staff will visit children weekly for 3 years to give doses of study medication and check for TB symptoms. At the end of the study, rates of LTBI will be compared between children who received vitamin D vs placebo. 3) Potential applications and benefits If results are positive, vitamin D could be used to prevent LTBI in children. Vitamin D deficiency affects 1 billion people worldwide, and 2 billion are estimated to have LTBI: results of our study could therefore have global importance. Several groups could benefit from the study. Vitamin D deficient people at risk of TB would benefit from the discovery of a cheap, safe method of reducing their TB risk. The TB control community would benefit from the discovery of a new tool for TB control. TB researchers would benefit from new scientific insights into the effects of vitamin D. Study participants will benefit, as they will receive screening for TB which they would not otherwise have had.
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