The suspension of a different batch by Italy was attributed to a man in Sicily, who died after being shot. It is not clear whether a blood clot was involved.
More than 142,000 people in Denmark, which has a population of around six million, have been injected with the vaccine produced by AstraZeneca.
Danish Health Minister Magnus Heunicke said on Twitter that “it is currently not possible to conclude if there is a connection.” He added: “We acted early, this needs to be investigated thoroughly.”
Denmark had already reduced its goal of ending its immunization campaign, in part because of delays in deliveries. The security break will delay you even more.
The AstraZeneca vaccine was examined for possible safety problems last year, while it was being tested in clinical trials. Two vaccinated volunteers in Britain developed neurological symptoms consistent with transverse myelitis, an inflammatory syndrome that affects the spinal cord and is often caused by viral infections.
These concerns temporarily ended global testing of the vaccine, but the investigations found no evidence linking the symptoms to the vaccine. One of the participants who fell ill was later found to have an undiagnosed case of multiple sclerosis.
More than 70 countries have already authorized the vaccine, with the notable exception of the United States, where regulators are awaiting data from a large clinical trial scheduled for the coming weeks. The Food and Drug Administration’s decision to authorize AstraZeneca’s vaccine is likely to take more than a month.
The most comprehensive real-world data on the safety of the vaccine comes from Britain, which administered 9.7 million doses last month. The British drug regulator, the Medicines and Health Products Regulatory Agency, said: “The number and nature of the suspected adverse reactions reported so far are not uncommon compared to other types of vaccines used routinely.”
Rebecca Robbins reported from Bellingham, Wash., and Thomas Erdbrink Amsterdam. Jason Horowitz and Emma Bubola contributed with reporting from Italy, Benjamin Mueller from London and Denise Grady from New York.