New TB vaccine offers glimmer of hope to HIV positive people

[Guest guest]

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. 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. 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.

Copyright 2000 - 2008 The Hindu

http://www.thehindu.com/2008/10/24/stories/2008102455451100.htm