The problem is that such experiments themselves risk spreading virulent flu in the population, and even causing a pandemic. Earlier this month, researchers in Wisconsin published a study in which they produced several new viruses, some of which — in ferrets — were both contagious and comparably deadly to the 1918 flu that killed tens of millions of people worldwide. Unlike experiments with anthrax, creating such flu strains in the lab presents a danger that affects us all, because once it is out, such a strain would be extremely hard to control. The researchers involved note that their labs are very safe, and they are. But “very safe” does not mean the risk is zero.

The virologists conducting these experiments say that by learning about how flu transmits in ferrets, we will be able to develop better vaccines and spot dangerous strains in birds before they become pandemic threats.

But developing good vaccines depends more on learning to induce effective immune responses than on finding out which genetic sequences make a virus transmissible. Dozens of effective vaccines protect us against microbes for which we have little understanding of the precise genetic requirements for transmission. The benefits for surveillance are speculative, too. Most flu strains circulating in birds are never sampled and most scientists must wait months or longer to gain access to the sequences of those that are.

More fundamentally, these experiments do not give us a reliable guide to predicting which of the many strains circulating in animals pose a danger to humans. The science is nowhere near the stage where a list of genetic “danger signs” can be crosschecked with flu viruses infecting birds to identify high-risk viruses. Indeed, time after time, flu viruses surprise us, having biological properties we don’t expect from what we know of their genetic sequence.

Such limitations in our ability to apply the scientific insights from these studies might be acceptable if the experiments themselves were safe. But creating a new, contagious strain of flu that is highly deadly carries unique dangers.