A new study by the researchers of the University of Oxford has found that the risk of developing blood clots after being infected with COVID-19 outweighs the risk of the Pfizer-BioNTech and AstraZeneca-Oxford vaccines, according to The Guardian.

The study, published in the British Medical Journal, looked at data from more than 29 million people in England and compared both vaccines with infection from the virus. They analyzed the rates of hospitalizations or deaths from blood clots and other blood disorders within 28 days of either a positive test or receiving the first jab.

The study’s lead author Prof. Julia Hippisley-Cox said, “People should be aware of these increased risks after COVID-19 vaccination and seek medical attention promptly if they develop symptoms, but also be aware that the risks are considerably higher and over longer periods of time if they become infected with SARS-CoV-2.”

Prof. Hippisley-Cox is an epidemiologist at the University of Oxford.

The researchers looked at the risks such as thrombocytopenia (low platelet count), blood clots, cerebral venous sinus thrombosis (CVST), and ischemic stroke.

The team found an increased risk of thrombocytopenia and other rare blood clots after a first dose of the AstraZeneca-Oxford vaccine. And they found a higher risk of blood clots and ischemic stroke after the first dose of the Pfizer-BioNTech vaccine.

However, the findings showed that there would be 934 extra cases of thrombocytopenia for every 10 million people after COVID-19 infection compared to 107 after the first dose of the AstraZeneca-Oxford jab.

In addition, there would be an estimated 1,699 extra cases of ischemic stroke for every 10 million people after COVID infection, compared to only 143 extra cases after the first Pfizer-BioNTech shot.

In general, blood clots can be developed in people without COVID-19 infection or vaccination. The blood clot risk described in this study is the additional risk brought by the infection or vaccines.

The researchers said the blood clot risk associated with the vaccination was relatively short-lived.

Senior researcher Prof. Carol Coupland said that the risk of stroke after the first dose of the Pfizer-BioNTech vaccine was elevated for 15 to 21 days, while the risk of thrombocytopenia after the first dose of AstraZeneca-Oxford jab was higher for 8 to 14 days.

On the other hand, the risks associated “with infection appeared to be generally over a whole 28-day period after the infection,” Prof. Coupland added. The article appeared in The Guardian.