Denmark will not use AstraZeneca’s COVID-19 vaccine for two weeks after reports that some recipients had developed serious blood clots, and in one case may have died as a result, the country’s authorities said on Thursday. They did not say how many reports of blood clots there had been, but Austria has stopped using a batch of AstraZeneca shots while investigating a death from coagulation disorders and an illness from a pulmonary embolism.