As a precaution, national health authorities may sometimes temporarily suspend the use of a vaccine batch or a vaccination campaign in the course of the investigation of a severe adverse event or a cluster of adverse events following immunization. In most cases, the investigation will lead to a different explanation and a causal relation between the event and the vaccine will not be found. Concretely, the detection of a series of thromboembolic cases coincidental in time with vaccination in Austria, in Denmark, or elsewhere in the first quarter of 2021 has led to the opening of an investigation and a precautionary suspension of the use in a few countries of the vaccine batch distributed to European Union countries.
However, the Pharmacovigilance Risk Assessment Committee of the European Medicines Agency has conducted a preliminary review of data and stated that there is no indication that vaccination caused these conditions, which are not listed as side effects with this vaccine. It also stated that the number of thromboembolic events — marked by the formation of blood clots — in people who have received the AstraZeneca vaccine is no higher than that seen in the general population, with a total of 30 cases among the 5 million people who have received the AstraZeneca vaccine in the European Economic Area. No other stringent national regulatory agency has established any specific alert related to vaccination with the Oxford Astra-Zeneca vaccine and the immunization campaign continues normally in most countries.