AstraZeneca Follows Up With German Lab on Vaccine Clotting Links Todd Gillespie, Bloomberg News Vials of the AstraZeneca Plc Covid-19 vaccine at a vaccination drive hosed by Indonesian Retail Merchants Association in Jakarta, Indonesia. , Bloomberg (Bloomberg) -- AstraZeneca Plc is following up with a German laboratory that may have discovered the cause of rare blood clots linked to its Covid-19 vaccine. The U.K. pharma company said the theory put forward by the Goethe University lab in Frankfurt on Wednesday is one of many that AstraZeneca scientists are investigating. âWe are continuing to work with regulators, recommending bodies and the scientific community around the world to understand more about the epidemiology and the possible mechanisms behind these extremely rare events,â said Fiona Cookson, a spokesperson for AstraZeneca.