This story is part of a series: Inside Ireland's Covid Battle The evolution of a new strain of virus has seen medics here, just like their colleagues around the world, presented with the most unpredictable challenges when treating Covid-19 patients.
Doctors and nurses working on the frontline have described how patients who, for all intents and purposes, appear to be on the road to recovery, suddenly and without warning, deteriorate before their very eyes.
Like Dublin man Joe Smith. He went to St James's Hospital on Easter Monday having experienced kidney pain at home. During his stay he was diagnosed with Covid-19 and was admitted to the hospital's Covid Intensive Care Unit.