IMAGINE being able to instantly round up your existing supply of antibodies to fight any disease you choose. That scenario is a step closer to reality following the creation of molecules that transform mouse antibodies into potent cancer killers.

Most vaccines – like those for measles or smallpox – prompt the immune system to build a standing army of antibodies against a virus or bacterium by injecting a deactivated version of the bug into the body.

But it can take weeks or months to build up immunity, and you have to catch people before they get infected. What’s more, the approach doesn’t …