AstraZeneca Vaccine and Blood Clots: What Is Known So Far

In rare cases, an immune reaction has led to antibodies that caused a serious clotting disorder. But public health experts maintain the vaccine’s benefits far outweigh the risks for most people.

The AstraZeneca-Oxford vaccine has been deployed against Covid-19 in at least 115 countries, some of them for several months now. But it wasn’t until a few cases of a rare blood-clotting disorder — some fatal — emerged within the past month or so that many European nations began to rethink its use across all age groups. Several of those countries, well stocked with alternate vaccines, have now limited use of the AstraZeneca-Oxford shot to older people, and a few have stopped using it altogether. While the incidence of these clotting disorders is extremely low, regulators and researchers are trying to raise public awareness of certain symptoms — including headaches, leg swelling and abdominal pain — especially in younger people who have been vaccinated. Public health experts, however, have expressed concern that publicity surrounding the rare vaccine-related reactions will fuel hesitancy, a particular problem in Europe. They continue to emphasize that the AstraZeneca-Oxford vaccine’s benefits far outweigh the risks. In many nations, it is the only vaccine available.