Health - New TB vaccine offers glimmer of hope to HIV positive people

Jaya Shreedhar

It can reduce the risk of HIV-infected people falling sick with TB.

A new Tuberculosis vaccine that can reduce the risk of HIV-infected people falling sick with TB, has been developed by a U.S. National Institutes of Health-sponsored trial in Dar-es-Salaam. Announcing the results of the ‘Dar Dar’ trial of the prime boost Mycobacterium vaccae (MV) vaccine at the 39th Union World Conference on Lung Health in Paris recently, Executive Director of the International Union Against TB and Lung Diseases (IUATLD) Nils Billo said the re sults were among “the most exciting and promising for people living with HIV in recent times.”

The trial was a collaboration between the Muhimbili University of Health and Allied Sciences in Tanzania and the U.S. Dartmouth Medical School (DMS) and cited by the investigators as a fine example of North-South cooperation in responding to an international health problem.

The seven-year study enrolled about 2,000 HIV positive volunteers who had received childhood BCG and whose CD4 count was 200 or more cells per microlitre of blood. The CD4 is a white blood cell that plays a critical role in the immune response and is normally above 800 cells per microlitre. Half the volunteers received five doses of the Mycobacterium vaccae two months apart over a year. The other half acted as a control arm receiving a dummy vaccine or placebo. Dr. Ford von Reyn, Professor of Medicine, DMS and principal investigator of the study said, “the vaccine was found to boost lymphocyte counts and protect against all forms of definite TB among 20 of the 1,000 who received it. There is no risk of getting TB infection from the vaccine itself as it is an inactivated form. The technology used to create the vaccine is low cost and that will help ensure its affordability in those countries where it will be needed most.”

TB is the world’s leading cause of death among PLHIV. Over a third of the global total of 33 million PLHIV is co-infected with TB and will likely die without treatment. One in five people with a severely weakened immune system can develop active TB within a year, an extraordinarily high risk. The risk of TB goes up as immunity comes down.

Preventing HIV positive people from falling sick with TB ranks among the leading public health challenges in China, India and the countries of sub-Saharan Africa. People whose immunity is down because of HIV infection, can have TB that manifests in a very atypical way, for example, without a persistent cough. Such people miss getting diagnosed with TB at the health care services and can die as a result. If cases of TB among PLHIV are diagnosed, the chance of them getting cured of TB is much worse than among those without HIV infection. In Malawi, for instance, four out of ten TB patients with HIV co infection die before the completion of anti-TB treatment. People who complete anti-TB treatment and are pronounced fully cured of TB run a high risk of getting TB again, owing to their low immunity.

A TB vaccine that will afford permanent protection is badly needed. It is too early to know if the Mycobaterium vaccae vaccine can do that. “Our follow-up with the study volunteers shows that the vaccine is affording a 40 per cent protection so far in these three to four years. We need to study its durability,” observed Dr. Robert Horsburgh, Chairman, Department of Epidemiology, Boston University Department of Public Health.

It is clear that the M.vaccae vaccine will have a profound impact on TB control among PLHIV in India as elsewhere. Dr. Anthony Harries, Senior Adviser to the IUATLD said, “these results suggest that about 6,000 cases of TB can be averted among a population of 2 million PLHIV within three years if 50 per cent of them received it.” The current armamentarium to prevent TB consists of the BCG vaccine which is given to children at birth. While it protects children from acquiring serious TB, it does not afford much protection to adults. Besides, BC being a live vaccine, could theoretically cause TB in PLHIV. The only other weapon available is giving HIV infected patients a daily dose of a single anti-TB drug — Isoniazid — to prevent them from getting TB. This measure is acknowledged to fuel the spread of Isoniazid resistant TB, but is still adopted as the lesser of the two evils. “The new vaccine would overcome both these challenges. I see it becoming part of a whole package of pre-Anti Retroviral Therapy care that can keep people with HIV healthy for many years,” said Prof. Harries. It is for future research to unravel how the vaccine may benefit people with CD4 counts lower than 200. While the Dar Dar study focused on a group at high risk for TB, the potential of the new vaccine to prevent TB among HIV negative individuals in TB prevalent areas is open to exploration. Meantime, it may be two years before Mycobacterium vaccae will become available.