A leading Australian infectious diseases and vaccine expert has answered some of the growing questions about the country's vaccine rollout, including the topic of choosing between AstraZeneca and Pfizer. 9News talked with Associate Professor Paul Griffin, who has worked on COVID's frontline at the Mater Hospital in Brisbane. He has overseen more than 100 clinical trials of vaccine as a part of the Nucleus Network. READ MORE: 9News sat down with Associate Professor Paul Griffin, who has worked on COVID's frontline at the Mater Hospital in Brisbane. (Nine) With the number of blood clotting cases in Australia due to the COVID vaccine now in the double figures, how concerned should we be?