Still, German researchers have said these clots were more common in recipients of the AstraZeneca-Oxford vaccine than in people who had never received the shot.
What symptoms should doctors and vaccine recipients look out for if there are side effects such as blood clots?
European regulators had recommended that recipients of the vaccine seek medical help for a number of possible symptoms, including leg swelling, persistent abdominal pain, severe and persistent headache or blurred vision, and tiny spots of blood under the skin outside of the area where the Injection was given was given.
However, these symptoms were so vague that the UK emergency departments almost immediately saw an increase in patients worried they were as they were described. As a result, some emergency physicians have asked for more central guidance on how to deal with what they termed largely unnecessary hospital visits.
German researchers have described special blood tests that can help diagnose the disorder and have suggested treatment with a blood product called intravenous immunoglobulin, which is used to treat various immune disorders.
Drugs called anticoagulants or blood thinners can also be given but are not used frequently – heparin – because the vaccine-related condition is very similar to that rarely seen in people given heparin.
Do vaccines cause other bleeding disorders?
Other vaccines, particularly those given to children for measles, mumps, and rubella, have been linked to transient low levels of platelets, an essential component of blood clotting.
Reduced platelet counts have been reported in a small number of patients who received the Moderna, Pfizer-BioNTech and AstraZeneca vaccines. One recipient, a doctor in Florida, died of a cerebral haemorrhage when his platelet counts failed to restore, and others were hospitalized. US health officials have stated that the cases are being investigated, but they have not reported the results of those reviews and have yet to advise that they are linked to the vaccines.