Tuberculosis (TB), an airborne disease caused by Mycobacterium tuberculosis, is one of the top ten leading causes of mortality globally. From the World Health Organisation (WHO) Global tuberculosis report 2020, 10 million people developed TB in 2019. 1.4 million people died of TB disease; 820,000 people living with HIV developed TB in 2019. Researchers estimate that a quarter of the world’s population may have TB infection.
Due to the increased availability of antiretroviral medications, the number of TB cases have reduced worldwide. However, the infection is still a burden in low- and middle-income countries. It accounted for about 97% of the TB in 2019.
In Uganda, TB incidence is 200 per 100,000 population with a mortality rate of 35 per 100,000 population. Out of the estimated 100,000 TB cases in the country, we notified only 65,897 in 2019. The emerging drug-resistant TB is a growing public health crisis. The WHO estimates that 1% of the new cases and 12% of those previously treated were drug-resistant TB in 2019. Uganda initiated treatment for drug-resistant TB to 384 patients, of whom 74% got cured.
A century after developing it, Bacille Calmette-Guérin (BCG) vaccine is the only licensed TB vaccine to date. We use it to prevent TB disease in infants and children but, its efficacy is variable. No vaccine exists to prevent TB among adults. Adults and adolescents are the most vulnerable population to acquiring and spreading TB.
However, we are optimistic that a TB vaccine may be around the corner. When adolescents received a second shot of the BCG vaccine in a phase II trial in South Africa in 2018, sustained TB infections occurred less. In another phase IIb study, an adjuvanted TB vaccine candidate (M72) protected the participants against active disease. It had an efficacy of 50%. The findings are fascinating.
Follow-up studies are warranted. And if they confirm the preliminary results, they will provide scientists with incredible intuition to render advancements into securing an effective TB vaccine.
That said, according to IAVI, three clinical trials are testing three novel TB vaccines.
- A live, attenuated MTBVAC vaccine candidate is undergoing a phase Ib/IIa dose-defining safety and immunogenicity study in South Africa. Scientists are comparing it with BCG in adults with and without latent TB infection.
- In South Africa and Tanzania, there’s a phase II study among adults using H56 TB protein vaccine candidate together with the IC31® adjuvant to ascertain if it decreases the rate of recurrent TB disease in HIV-uninfected adults already successfully treated for pulmonary TB.
- The vaccine candidate VPM1002 is undergoing a phase III study in Gabon, Kenya, South Africa, Tanzania, and Uganda. Scientists aim to evaluate its efficacy and safety compared to BCG in preventing TB infection in HIV- exposed and HIV-unexposed newborn infants.
Unlike COVID-19, no one has naturally recovered from TB disease. We must bridge the funding gap if we want to realise an effective TB vaccine soon.