The study, reported by medical journal Lancet, was conducted on 2,794 South African infants as part of the randomised phase II trials between July 15, 2009 and May 4, 2011. This was the first big study on infants since the Bacillus Calmette-Guerin (BCG) vaccine was introduced in 1921. South African experts who were conducting the trials said the reason for failure needs to be explored.
The impact of this failure on India could be debilitating as it is the highest TB burden country, accounting for 21 per cent (2.2 million cases) of the total global cases (about 8.7 million a year). This despite the fact that BCG vaccine is part of the universal immunisation programme of the government of India. The vaccine is believed to be 80 per cent effective in preventing TB infection.
The candidate vaccine failed to protect South African infants who had already had BCG. Apparently it induced modest immune responses against TB in infants but were insufficient to protect them against the disease. The responses were much lower than those previously seen in adults.
The trials were conducted by the South African Tuberculosis Vaccine Initiative, Institute of Infectious Disease and Molecular Medicine, and School of Child and Adolescent Health, University of Cape Town.
“This is the first efficacy trial of a new TB vaccine since BCG, a significant step in itself, and there is much that we and others can learn from the study and the data it has produced,” said Helen McShane of the University of Oxford who developed the vaccine.
The Lancet authors however left a window of hope especially with respect to the vaccine’s dismal performance. They reasoned that since infants are not the most responsible group that transmit infection, there is a chance that MVA85A could “potentially protect” adolescents or adults against TB.
This is based on the fact that “immunologically immature infants don’t respond as well to this vaccine as adults do”.
“MVA85A could also potentially have high efficacy in people of all ages against severe forms of TB, including pulmonary tuberculosis, without preventing infection or mild forms of disease,” the world’s leading medical journal noted.
The important finding of the trial, they argued, is the safety of the vaccine.