Tuberculosis Vaccines

Tuberculosis is a major concern across the world because of the virulence of the disease and its potential for a fatal outcome. It is estimated that as much as a third of the world’s population bears some form of the disease, 10% of which will suffer from an activated condition that could be fatal. The problem presented by TB is further compounded by the spread of drug resistant strains of the bacterium responsible for the disease.

BCG is the vaccination currently employed across the world to prevent the spread of TB. Unfortunately BCG’s effectiveness has proven to be extremely variable, and the reasons for this remain unclear. There is a growing need for a method of immunising against TB that is universally effective, and with which the disease can be eliminated through global vaccination programmes.  This article looks at some of the vaccines currently being developed to replace BCG.

Alternatives to BCG: MVA85A

MVA85A is one of a number of new, up and coming vaccines that will hopefully help in the prevention of tuberculosis. This vaccine is under development at Oxford University, and has been shown to be both safe and effective in combination with BCG.

MVA85A is also known as modified vaccinia Ankara 85A, it is an excellent example of a new class of vaccination technologies being developed. The vaccine is made up of a modified version of the Ankara virus which carries a molecule called an antigen, a substance found on the surface of the bacterium which causes tuberculosis. The body recognises the antigen and responds to it as if it were an actual infection, thereby acquiring immunity against the actual disease without being exposed to it.

Such a vaccine has the advantage of remaining safe for use even amongst vulnerable populations like the immunocompromised, a group of patients who cannot safely receive the existing BCG vaccine.

Phase I trials of this vaccine have been successful and phase II trials are currently underway.

Alternatives to BCG: rBCG30

This vaccine was devised at UCLA and takes a different approach towards immunising against tuberculosis. rBCG30 is an abbreviation for recombinant Bacillus Calmette-Guerin, and is a vaccine derived from the BCG vaccine currently used across the world to immunise against TB. Unfortunately BCG has two main drawbacks, the first is the fact that its effectiveness varies extensively from region to region across the world, the second is that BCG is composed of live, attenuated virus, which makes it unsafe for use amongst certain, at-risk populations.

rBCG30 attempts to stabilise the effectiveness of BCG, and make it suitable for use amongst a broader range of people, by deriving an antigen from the strains of tuberculosis bacteria used for immunisation.

Alternatives to BCG: 72F fusion protein

The 72F fusion protein vaccine takes a similar approach to that of the vaccines mentioned so far in this article. The creators have attempted to generate a vaccine derived from components of the tuberculosis bacterium. A fusion protein is a larger protein generated from the unison of two smaller ones, in this case, both antigens from the surface of the tuberculosis bacterium. The use of two antigens can generate a powerful and lasting immunisation.

Unfortunately while there are a number of different candidates for a future tuberculosis vaccine, few of these have progressed far enough in the development process to promise a real alternative to BCG anywhere in the near future. Technologies and our understanding of vaccines and bacteria are constantly improving, which means that as time goes on better replacement vaccines will undoubtedly be developed.

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