Researchers at the Greifswald teaching hospital in northern Germany said that they had discovered the cause of the unusual blood clotting found in some recipients of the AstraZeneca coronavirus vaccine.
The investigation showed how the vaccine caused rare thrombosis in the brain in a small number of patients.
The discovery means that targeted treatment can be offered to those who suffer similar clotting, using a very common medication.
The researchers emphasized that treatment would only be possible in patients where blood clots appear, rather than as a preventative treatment.
The information has been shared with hospitals around Europe.
Symptoms like continuous headache, dizziness or impaired vision lasting more than three days after vaccination need further medical check-ups, according to the German Research Association for Thrombosis and Hemostasis in a statement on the recent findings.