21 April 2021 - 09:27 By Reuters The EMA said on Tuesday it suspects the vaccine may trigger an unwanted immune response, but safety committee chairwoman Sabine Straus said it has not identified specific risk factors. Image: REUTERS/DADO RUVIC A German scientist studying extremely rare blood clots linked to AstraZeneca's Covid-19 vaccine said on Tuesday Johnson & Johnson has agreed to work with him on the research after similar serious side effects emerged in recipients of its shot. Andreas Greinacher, a transfusion medicine expert at Greifswald University, announced the collaboration after the European Medicines Agency said it would add a label to J&J's vaccine warning of unusual blood clots with low platelet counts. AstraZeneca's shot has a similar warning.