Aids researchers and advocates were devastated in 2007, when a much anticipated vaccine against HIV unexpectedly failed to protect anyone in a clinical trial of 3,000 people. Even worse, the experimental inoculation, developed with money from the Merck pharmaceutical company and the National Institute of Allergy and Infectious Diseases, actually increased the chances that some people would later acquire HIV. Millions of dollars and more than a decade of research had gone into creating the vaccine. Meanwhile, in that same 10-year period, 18 million people died of AIDS, and millions more were infected.
The Merck vaccine failed in large part because investigators do not yet know how to create the perfect vaccine. Yes, a number of vaccines have been spectacularly successful. Think of polio and smallpox. In truth, though, luck played a big role in those successes. Based on limited knowledge of the immune system and of the biology of a pathogen, investigators made educated guesses at vaccine formulations that might work and then, perhaps after some tinkering, had the good fortune to be proved right when the vaccine protected people. But all too often lack of insight into the needed immune response leads to disappointment, with a vaccine candidate recognized as ineffective only after a large human trial has been performed.