October 9, 2014
Worldwide tuberculosis rates have been on a steady decline in recent years, but as resistance to commonly used antibiotics to treat the disease grows, most scientists and health advocates argree that a vaccine is the best route for prevention.
A new study suggests that a tuberculosis vaccine with low efficacy in adolescents and adults could be more successful at reducing rates of the disease than a vaccine intended for infants.
Using a model with data from 91 countries, researchers from the London School of Hygiene and Tropical Medicine and the World Health Organization found that vaccines targeted at adolescents and adults could prevent TB and be cost-effective, and even save money, before 2050 if the efficacy were as low as 20% with a 10-year duration.
Detailed in the Proceedings of the National Academy of Sciences, the researchers estimated that a 10-year duration vaccine with 60% efficacy could prevent 17 million cases of TB between 2024 and 2050 in low-income countries. By contrast, if a vaccine were targeted at infants, the model suggests that fewer than one million cases of TB would be averted. Since adolescents and adults are the main sources of the spread of TB, the authors say prevention is key in this population.
There is only one vaccine against TB in existence, the Bacillus Calmette-Gu¨¦rin vaccine, or BCG. The vaccine is recommended for infants, but its effectiveness varies widely, anywhere from 0% to 80% for a duration of 15 years. BCG can prevent TB that has spread beyond the lungs, but it's not reliable against pulmonary TB, the most severe form of the disease. Another problem with BCG is that its protective effect seems to vary according to geography and the laboratory in which the vaccine strain was grown. It also becomes less effective with age, so BCG is rarely given to adults because it's less effective in older people.
Research to develop new, more effective TB vaccines has proven difficult. While many candidates have been effective in animals, up to two-thirds of the world's population is already infected with the bacterium that causes tuberculosis. So vaccines intended to be administered before exposure are not likely to have much of an impact of curbing TB rates in endemic areas.