I've been following the story about the scientists who have been working to figure out how H5N1 bird flu might become transmissible from human to human, the controversial research they used to study that question, and the federal recommendations that are now threatening to keep that research under wraps. This is a pretty complicated issue, and I want to take a minute to help you all better understand what's going on, and what it means. It's a story that encompasses not just public health and science ethics, but also some of the debates surrounding free information and the risk/benefit ratio of open-source everything.

H5N1, the famous bird flu, is deadly to humans. Of the 566 people who have contracted this form of influenza, 332 have died. But, so far, the people who have caught bird flu don't seem to have contracted the disease from other humans, or passed it on. Instead, they got it from birds, often farm animals with whom the victims were living in close contact. H5N1 was first identified 14 years ago, and there's never been a documented case of it being passed from person to person.

But that doesn't mean such a leap is impossible.

That's because of how the influenza virus works. Influenza is made up of eight pieces of RNA, containing 10 genes, and they all replicate independently of one another and there's no system for error correction*. That means you have more opportunity for mutations to arise that change what the virus does and who it can infect. Think of it like dice. Genetic replication is like putting a die in a jar, shaking it up and seeing what you get. Everybody does that. But influenza has eight die, not one. So it accumulates mutations faster. As a bonus, influenza viruses that infect the same host can share genes—essentially creating a baby virus that carries traits from different parents.

That's why, despite 14 years of relatively low-risk behavior, scientists are still concerned about what H5N1 might do in the future. All it would take, theoretically, is the right roll of the dice, and suddenly you have a flu virus with a 60% kill rate that can pass from person to person.

At least, theoretically. Could that actually happen? And, if so, how likely is it that the "right" bad combination of genes will come up? You can see why these are important questions to ask, and that brings us to the controversy.