NEW DELHI : Shares of Astrazeneca Pharma India Ltd on Wednesday tumbled more than 13% after its parent firm announced pausing COVID-19 vaccine trials globally due to an unexplained illness in a study participant.On the BSE, the Astrazeneca stock fell 13.40% to Rs3,650; and on the NSE, it tanked 12.31% to Rs3,710.Late on Tuesday, AstraZeneca Plc said it was pausing late-stage trials of its COVID-19 vaccine candidate developed with the University of Oxford.According to a New York Times report, a participant based in the United Kingdom was found to have transverse myelitis, an inflammatory syndrome that affects the spinal cord and is often sparked by viral infections.The COVID-19 vaccine was widely seen as one of the leading vaccine candidates.