Data from Historic Phase IIb Clinical Trial for Tuberculosis Vaccine Candidate MVA85A Published in the Lancet

By Eric Akasa                                                                                                                                                                                                                                                                                                                                                                                                                                                              Data were published in The Lancet from a Phase IIb clinical trial evaluating the safety and efficacy of MVA85A in preventing tuberculosis (TB) in infants. MVA85A is a TB vaccine candidate designed to boost immune responses already primed by the Bacille Calmette-Guérin (BCG) vaccine, the currently licensed and widely used TB vaccine.

Data show that a single dose of MVA85A is not sufficient to confer statistically significant protection against TB disease or infection in infants who had been vaccinated at birth with BCG. There were 32 cases of TB disease in the infants that received BCG + MVA85A compared with 39 cases of disease among those receiving BCG + placebo. Non-significant vaccine efficacy was measured at 17.3% (95% CI -31.9% to 48.2%) at study completion. The vaccine candidate also did not provide statistically significant protection from infection with Mycobacterium tuberculosis, the bacterium that causes TB, which was a secondary efficacy endpoint.

“Although the results of this first efficacy trial of a new TB vaccine are not what we had hoped for, further analysis of the data should reveal a great deal about how the body’s immune system protects against TB and what is necessary to develop an effective vaccine,” said senior author Prof. Helen McShane, a Wellcome Trust Senior Clinical Research Fellow at the University of Oxford and the original developer of the vaccine. “The results from this study should let us know far more about the type and level of immune response required, and that will boost future efforts to develop an effective TB vaccine by Oxford and other researchers throughout the world. The difficulty of this task is one reason why there has not been a new TB vaccine since BCG was developed more than 90 years ago, but one is still urgently needed and I’m not about to give up now.” She adds.

MVA85A is the first novel, preventive TB vaccine candidate since BCG to complete a Phase IIb safety and efficacy study.

The study was successful in that the vaccine was well tolerated, there was no evidence of any harm to the trial participants, and it gave a clear answer. This study also showed it is possible to conduct a large infant efficacy clinical trial in an area of high TB incidence with robust endpoints for detecting disease, something that is expected to greatly benefit future testing of TB vaccine candidates.

Funding for this clinical trial was provided by Aeras, a nonprofit biotech with a social mission to develop TB vaccines, The Wellcome Trust, and the Oxford-Emergent Tuberculosis Consortium (OETC), a joint venture between the University of Oxford and Emergent Bio-Solutions. This Phase IIb study was sponsored by Aeras and conducted by the University of Cape Town’s South African Tuberculosis Vaccine Initiative (SATVI). The vaccine was originally developed and investigated by the University of Oxford.

It is anticipated that further analysis of the data and samples collected will be conducted for information that may be helpful for the development of new vaccine candidates. For example, blood samples will be used to identify markers that can predict whether a child will develop TB disease in the future. These biomarkers are termed “correlates of risk” and may substantially aid the development of new vaccines and contribute to different trial designs in the future.

 “Vaccine development is an incredibly difficult undertaking, and the scientific community has only become fully engaged in the development of TB vaccines in the last decade,” said Tom Evans, MD, Aeras interim CEO. “Because of the urgency to control the global TB epidemic, and despite these trial results, we remain steadfast in our belief that an improved TB vaccine will be developed and represents the best hope for eliminating the disease. The valuable scientific understanding gained from this trial will provide crucial information for the robust global portfolio of more than a dozen other TB vaccines undergoing clinical testing, a number that was unimaginable a decade ago.” He adds.

 “While we are clearly disappointed in the results announced today, this study does demonstrate that a large-scale clinical trial testing a vaccine in infants can be designed and run efficiently, adhering to the highest standards of good clinical trial practices in a setting with a high TB burden,” said Dr. Steve Chatfield, EVP and president of the biosciences division at Emergent Bio-Solutions, and chairman of the Oxford-Emergent Tuberculosis Consortium. “We are proud to have been part of this broad international collaboration that brought together academic, product development, manufacturing, and clinical trial expertise in an effort to make a positive impact on global health.”

 “Completion of the study has been a significant achievement by the MVA85A development partners and demonstrates the advantages of collaboration through a public-private partnership model to address global public health challenges,” said Dr. Jacqui Shea, general manager of OETC. “While MVA85A has not met its efficacy goal, this study should enable the TB vaccine community to better understand the immune response against TB and help to design future efficacy studies.”

According to Prof. Willem Hanekom, director of the South African TB Vaccine Initiative (SATVI), “We are proud to have completed the first efficacy trial of a new TB vaccine in 90 years, and believe the results will guide the TB vaccine field in the future,” “The TB epidemic in our country is devastating – half a million South Africans develop the disease every year. Prevention by an effective vaccine would be the best way to get the epidemic under control. With this goal in mind, our group will continue to test multiple new vaccine candidates in the Worcester area. We are very grateful for the commitment of the local community in this effort.” Hanekom adds.

Dr. Ted Bianco, Director of Technology Transfer at the Wellcome Trust, said that it is no mean feat to design and implement a trial of this kind and obtain a result as unequivocal as this. It is only through the difficult business of evaluating candidate vaccines in humans that we will really move forward in understanding how we might improve on BCG. I stand in admiration of the professionalism of this international team that understands the importance of well executed science, irrespective of the result one might have hoped for.

Study Design
This Phase IIb study was a double blind, randomized, placebo-controlled trial investigating the safety, immunogenicity and efficacy of MVA85A in BCG-vaccinated infants.

The study, which began in 2009, was the first to evaluate MVA85A’s ability to prevent TB disease following BCG vaccination. The study, in infants without TB disease or HIV infection, involved a ‘prime-boost’ strategy that used MVA85A to boost immune responses already primed by the BCG vaccine.

The study enrolled nearly 2,800 HIV-negative infants in the Western Cape province of South Africa. All of the infants that participated in the study received BCG at birth and then one half of the infants received a single dose of MVA85A at 4-6 months of age and the other half received a placebo (Candida skin test antigen). Approximately 93% of the infants enrolled completed the study and have been monitored for up to 37 months for any signs of TB disease. MVA85A was generally well tolerated and the vaccine had a safety profile comparable to other pediatric vaccines. The most frequent side effect observed was mild redness or swelling around the injection site following vaccination.

MVA85A is also being investigated in a Phase IIb efficacy study in people living with HIV in Senegal and South Africa, a Phase IIa study in infants born to HIV positive mothers in South Africa, and Phase I studies in the UK.