Just about any research with microorganisms might inadvertently cause them to gain a new function. Introducing mutations with the purpose of knocking out a gene might simultaneously and unexpectedly confer the microbe with a new ability. Even the simple act of passaging a microbe in animals in the laboratory can and often does cause them to gain new functions. If we cannot do any of these things, then we might as well just close down all of our biomedical research facilities.

The problem, then, isn’t gain-of-function research per se, but “gain-of-virulence” research. In other words, research with the intention of making a dangerous microbe more dangerous can be extremely risky research, particularly if it involves airborne or otherwise highly contagious microbes. So, should we therefore ban all gain-of-virulence research?

Even here, the answer is “no.” Some or even most kinds of gain-of-virulence research are potentially very valuable. For instance, it could be quite useful if scientists knew in advance what sorts of mutations in a virus could make it deadlier. That way, epidemiologists could watch for these mutations as new strains inevitably arise. Another example is the creation of highly virulent or contagious microbes with the purpose of creating vaccines and antivirals that guard against the worst possible strain, just in case something that nasty evolves on its own in nature.