A new tuberculosis vaccine, MVA85A, has recently been found to be less effective than initially thought, prompting widespread consternation in the press. The excellent NHS Choices website reports that “although the stories are based on solid science, the news is actually less worrying than the headlines suggest”. MVA85A is a booster vaccine that researchers hope might help improve the effectiveness of the existing BCG vaccine. Although the BCG is effective in the UK, new vaccines and boosters are needed as it is less effective in other countries. The effectiveness of BCG against tuberculosis is variable and has been found to be less effective in countries such as South Africa, where as many as 1% of the population has TB. An effective booster vaccine would therefore be useful. Although a recent study found the new vaccine is safe, it does not appear to have performed better than the placebo in children who had already had the BCG vaccine. Despite this setback, several further lines of investigation are being pursued by researchers, who now want to look at whether the MVA85A vaccine might work better in other sub-populations, and whether it might improve protection against pulmonary tuberculosis (lung infection) in people who have HIV, for example.
Another paper just published has found that whole genome sequencing of Mycobacterium tuberculosis provides more accurate information on clustering and longitudinal spread of the pathogen than the standard test (classical genotyping). Importantly, whole genome sequencing revealed that first outbreak isolates were falsely clustered by classical genotyping and do not belong to one recent transmission chain. By using whole genome sequencing, the authors estimated that the genetic material of M. tuberculosis evolved at a rate at 0.4 mutations per genome per year, suggesting that the bacterium grows in its natural host (infected people) with a doubling time of 22 hours, or 400 generations per year. This finding about the evolution of M. tuberculosis indicates how information from whole genome sequencing can be used to help trace future outbreaks. Importantly, as the costs of whole genome sequencing are declining, this test could soon become the standard method for identifying transmission patterns and rates of infectious disease outbreaks.
Whole Genome Sequencing versus Traditional Genotyping for Investigation of a Mycobacterium tuberculosis Outbreak: A Longitudinal Molecular Epidemiological Study. (2013) PLoS Med 10(2): e1001387. doi:10.1371/journal.pmed.1001387