Tuberculosis is the world's deadliest infectious disease, sickening eight million people and killing two million every year. A century-old vaccine prevents childhood forms of the disease. But there's a desperate need for a vaccine that's effective against the adult form of the disease, which is highly contagious and is growing resistant to drug treatment. Renewing hope on this front, two human trials of vaccines that could be protective against the adult form of the disease began in the United States earlier this year.

Select from the choices above to read the entire article.