In July 2021, one of the mega-mergers familiar to the pharmaceutical industry closed when the British-Swedish group AstraZeneca completed its $39 billion half-cash, half-shares acquisition of Alexion. Alexion Pharmaceuticals was until then a Boston-headquartered and New York-listed company doing the majority of its business in the US. Now operating as the rare diseases division of AstraZeneca, Alexion has retained Boston as its head office.  Yet company documents now available for 2021 show that when it comes to money, Alexion is a largely Irish business. Based at the group’s Blanchardstown global operations headquarters in Dublin,  Alexion Pharma International Operations has been…