Medical breakthroughs: chance and opportunity

Medical advances of great importance in improving diagnosis, treatment or prevention of disease are often called 'breakthroughs'. The processes by which breakthroughs are achieved are multiple, but may include necessity (a problem which must be solved), opportunity (the time must be right), chance (the unexpected), curiosity (a desire to understand mechanisms) and ingenuity (ability to find a solution). Discovery can be the start of a chain reaction, so that the breakthrough at the end of the chain becomes "inevitable". Two examples are given in which these attributes played a part (i) the development of a vaccine against the poliomyelitis virus and (ii) the harnessing of penicillin as a therapeutic agent to treat serious bacterial infections.