A different animal?

For the second time, macro factors will make it hard to divine how much impact, if any, a clinical failure at Circassia Pharmaceuticals plc will have on investor sentiment in the U.K. But at least two differences between Circassia and previous British implosions may help limit the fallout.

Last month Circassia abandoned the technology that had been the basis for its gigantic 2014 IPO. The £200 million ($334.2 million) deal was the largest-ever IPO for a U.K. biotech and valued Circassia at £581 million ($970.8 million)...