There is a vaccine for tuberculosis available that has saved many, many lives but it has an odd feature — in some people it just doesn’t work. That would be fine if it didn’t work in a few people, as happens with many vaccines, but in some parts of the world, the vaccine has an 80 percent failure rate. What’s going on there?
Enter researcher Peter Andersen with a hypothesis about that as well as a lab full of mice to test it.
Andersen’s hypothesis was simple. The TB vaccine exposes human beings to a weakened version of Mycobacterium bovis — a from of TB that afflicts cows. Exposure to this causes an immune response which will also protect people from the human form of the disease.
So why doesn’t it always work. Well, in some parts of the world people frequently come into contact with Mycobacterium tuberculosis — the strain that causes tuberculosis in human beings — long before having the vaccine.
Andersen hypothesized that what was happening was this. Some people were being exposed to a weak strain of human TB. This produced an immune response which that rendered the vaccine ineffective. People were essentially being immunized against the vaccine. Then, later in life, they were still vulnerable to the human form of TB.
To test this theory, Andersen used a mouse model of tuberculosis. He infected mice with three strains of mycobacteria taken from a part of Malawi where the bovine version of the disease does not exist. Then, later, he exposed the mice to the Mycobacterium bovis vaccine. Lo and behold, the vaccination did not work. In each case, when later exposed to full blown tuberculosis, the mice all contracted the disease.
Vaccines made from dead versions of TB, however, did protect the mice. There are currently several vaccines being developed that used dead versions of TB rather than weakened versions of live virus, and Andersen’s research is the first suggesting that these vaccines might offer protection to people for whom the traditional vaccine will not work.
Source:
New TB vaccines ‘in pipeline’. The BBC, February 13, 2002.