SOME countries are restricting use of the AstraZeneca COVID-19 vaccine to certain age groups, or suspending use, after European and British regulators confirmed possible links to rare blood clots. Johnson & Johnson's vaccine has also been hit by concerns over blood clots. European regulators will issue findings later of their review into clotting issues in adults who had received the shot in the United States. U.S. health agencies recommended pausing the single shot's use temporarily on April 13 after reports of six cases in women under 50. A health advisory panel will meet on April 23 to discuss whether the…