Scientists in the UK have identified the markers associated with rare blood clots which have been linked to the Oxford/AstraZeneca vaccine.
The discovery could help treat the condition more effectively and increase survival chances.
Dur Sue Pavord of Oxford University Hospitals (OUH) led a team of experts, who have now set out guidance for clinicians which can help diagnose what they call vaccine-induced immune thrombocytopenia and thrombosis (Vitt).
Thrombocytopenia: A condition where the patient has a low count of cells that help the blood clot, known as platelets.
Thrombosis: Blood clots block veins or arteries and can lead to life-threatening conditions such as a stroke or heart attack.
But the experts said treatments such as plasma exchange, which involves removing straw-coloured liquid known as plasma from the blood and replacing it with new plasma fluid, can dramatically increase survival chances for those with severe disease.
Up to July 28 2021, the MHRA has received reports of 411 cases of major blood clots with concurrent low platelet counts in the UK following AstraZeneca vaccine. CVST was reported in 146 cases.
The overall case fatality rate was 18% with 73 deaths, six of which occurred after the second dose, the MHRA said.
At that time, the estimated number of first doses of AstraZeneca administered was 24.8 million while the estimated number of second doses was 23.6 million.
Dr Pavord, who is a consultant haematologist at OUH, said:
"Our study shows that for those who develop Vitt, it can be devastating: it often affects young, otherwise healthy vaccine recipients and has high mortality.<
"It is particularly dangerous when the patient has a low platelet count and bleeding in the brain."
She added: "Vitt is a very new syndrome, and we are still working out what the most effective treatment is, but identifying prognostic markers has helped to determine what is the more effective way to manage the condition."
For the study, the researchers evaluated 294 patients aged between 18 and 79, 220 of whom were classed as either definite or probable cases of Vitt.
All the patients had received the first dose of the AstraZeneca vaccine and with symptoms appearing five to 48 days after the jab.
The researchers said 85% of the patients studied were under the age of 60, many of whom had no underlying medical conditions.