According to the World Health Organisation, people ill with TB can infect 10–15 other people through close contact over the course of a year
A South African study has found that revaccination with the Bacille Calmette-Guerin (BCG) vaccine significantly reduces sustained TB infections in adolescents. Introduced in 1921, BCG is the only TB vaccine currently licensed.
The results of the phase II clinical trial conducted by Aeras, a non-profit organisation, will be presented at the 5th Global Forum on TB Vaccines that starts in Delhi tomorrow. In the prevention-of-infection Phase 2 trial conducted in South Africa, the experimental vaccine candidate, H4:IC31, also reduced sustained infections, although not at statistically significant levels. However, the trend observed for H4:IC31 is the first time a subunit vaccine has shown any indication of ability to protect against TB infection or disease in humans.
TB kills an estimated 480,000 Indians every year and more than 1,400 every day. India also has more than a million ‘missing’ cases every year that are not notified and most remain either undiagnosed or unaccountably and inadequately diagnosed and treated in the private sector. According to the World Health Organization (WHO), about one-third of the world’s population has what is called a latent TB infection, which means people have been infected by TB bacteria but are not (yet) ill with the disease and cannot transmit the disease. People infected with TB bacteria have a lifetime risk of falling ill with TB of 10 percent. People ill with TB can infect 10–15 other people through close contact over the course of a year. Without proper treatment, 45% of HIV-negative people with TB on average and nearly all HIV-positive people with TB will die.
The trial results though not statistically significant, offer hope of arresting the transmission of TB especially in populations in which infection rates are really high
Mark Hatherill, MD, Director of the South African Tuberculosis Vaccine Initiative (SATVI) at the University of Cape Town, and the study’s principal investigator, said: “We are pleased to have performed the first-known randomized, placebo-controlled prevention-of-infection trial for TB and to have demonstrated that vaccination has the potential to reduce the rate of sustained TB infection in a high-transmission setting. While neither vaccine proved to be statistically significant in preventing an initial TB infection, we are extremely encouraged by the signals observed for both vaccines in preventing sustained TB infections. We believe the results from this novel trial design will provide significant scientific benefit to the field in understanding TB infection, and based on this positive signal, we look forward to testing the potential of such vaccines to prevent TB disease among uninfected adolescents in a larger, more traditional prevention-of-disease clinical trial.”
The study involved 990 HIV-negative, healthy adolescents (12 to 17 years of age) who had been vaccinated as infants with BCG. All participants were randomized evenly into three study arms: placebo, H4:IC31, or BCG revaccination. All participants were screened to ensure they were not infected with Mycobacterium tuberculosis (Mtb) prior to vaccination in the study. The data showed that both vaccines appeared to be safe and produced an immune response in the adolescents studied. No vaccine-related serious adverse events were reported in the study, and the most common vaccine-related adverse event was injection site swelling in BCG revaccinated participants, typical for BCG vaccination.
Linda-Gail Bekker, a lead investigator for the trial, the Chief Operating Officer at the Desmond Tutu HIV Foundation and President of the International AIDS Society, said: “We would like to thank all the study participants and their families for participating in this novel clinical trial. We believe the results are important and warrant further investigation into other subunit vaccines and a reevaluation of BCG revaccination as a potential strategy to prevent TB in high-incidence countries. An effective TB vaccine remains an urgent global goal.”
