The eradication of smallpox was meant to be the harbinger of future triumphs over infectious diseases. But it’s looking more and more like a one-off. Polio was meant to have followed smallpox by 2000, but this deadline has been shifted forward several times.

Similarly, tuberculosis refuses to go away. As a recent Lancet review reminds us, a third of the world is infected with Mycobacterium tuberculosis, and two million people die from tuberculosis every year, even though the BCG vaccine has been available for more than 75 years. For reasons unknown, this vaccine doesn’t seem to “work” in much of the world. The …