With high hopes, a team led by the South African Tuberculosis Vaccine Initiative inoculated 2,797 infants in the country, half with a vaccine called MVA85A and half with a placebo.
The only vaccine currently available in the fight against TB is Bacille Calmette-Guérin, a live vaccine first used in 1921 and originally derived from a cow tuberculosis strain.
An inadequate vaccine is not the field’s only problem: the four main drugs currently used to treat tuberculosis are also decades old, take six months to rid the body of the bacilli, and are becoming obsolete due to the spread of multidrug-resistant and extensively drug-resistant TB. Despite the gloomy outlook, many researchers are still plugging away, through pharmaceutical-nonprofit partnerships and redesigned basic research efforts, to achieve a happy ending.
The failure of the MVA85A vaccine trial in South Africa last year was disappointing, but at least a dozen other TB vaccine candidates continue in clinical trials.
Most of these reflect one of two general strategies for preventing tuberculosis: improve the existing BCG vaccine or, more commonly, boost its effect with a secondary vaccine.
The MVA85A vaccine, for example, was a modified viral vector expressing Mtb antigen 85A designed as a booster to BCG. Vaccine development is hindered by lack of cellular or molecular markers that directly correlate with immune protection from TB, making it difficult to predict how well a vaccine might protect against TB based on the responses of a handful of individuals.
AERASWith TB drugs and vaccines still in early clinical phases, some scientists are going back to the basics to see if a better molecular understanding of the bacterium itself could assist these programs.