Countries around the world have been stockpiling the antiviral drug Tamiflu in preparation for a possible avian-flu pandemic. But a review published in the journal Lancet last week cast doubt on the drug’s effectiveness. Researchers in Rome analyzed existing studies and concluded there is no “credible evidence” that Tamiflu works against bird flu. While acknowledging that the drug has considerable limitations—to be effective, it must be administered soon after flu symptoms appear—the World Health Organization questioned the review’s conclusions, and said it won’t change its recommendation that governments keep stocking up on the drug. For now, there’s little choice: while Tamiflu isn’t a magic bullet, says Dr. Jeremy Farrar, a doctor in Vietnam who has treated bird-flu victims, “it remains the best drug we have.”