Researchers Investigate Link Between COVID Vaccine and Low Platelets

Oxford COVID vaccine
A vial of the Oxford/AstraZeneca vaccine Source: Vincenzo Livieri/IPA MilestoneMedia/PA Images

A population-based analysis has revealed a slightly increased risk of low platelets levels with the Oxford-AstraZeneca COVID vaccine.

Multiple countries around the world have initiated their COVID vaccine roll-out program in efforts to contain the pandemic. The forerunners among the vaccines are the Oxford-AstraZeneca, Pfizer-BioNTech, and Moderna vaccine. All of whom demonstrated vaccine efficacy of 90% and above in their clinical trials. Despite their effectiveness, the vaccines have met quite a bit of criticism. Mostly because of the adverse reactions that have occurred among vaccine recipients. Several reports of blood clots, low platelets, and even deep vein thrombosis have come forward after doses of the COVID vaccine. The majority of thromboembolic events have occurred with the Oxford Vaccine. Moreover, in March, multiple European countries even suspended the use of the Oxford vaccine due to the risk of blood clots.

Later on, researchers at the University of Oxford investigated the incidence of cerebral venous thrombosis (CVT) following the COVID vaccine and COVID-19 infection itself. They found the incidence of CVT as 5 per million people among Oxford vaccine recipients. However, the risk of blood clots was 8 times higher among the COVID positive patients.

Nevertheless, there is a lack of population-based evidence on the association of the COVID vaccine and thromboembolic events. Such as low platelets, CVT, and hemorrhagic events. Now, a team led by the University of Edinburgh has analyzed this link in a nationwide study conducted in Scotland.

The researchers analyzed around 2.5 million people who had received first dose of COVID vaccine between December 2020 and April 2021. Of these, 1.71 million people received Oxford vaccine, 0.82 million received Pfizer, and less than 10,000 people received the Moderna vaccine.

They published their findings in the journal Nature Medicine.

No Link Between Pfizer and Blood Clots

Results revealed a slightly increased risk of idiopathic thrombocytopenic purpura (ITP) with Oxford vaccine; 11 per million doses. ITP is a disorder characterized by low platelet levels. As a result, people are at an increased risk of bleeding and in some cases even clotting. ITP occurred more commonly among the older population and those with a chronic condition. However, the increased risk of ITP was still lower than the risk of developing the condition following COVID-19 infection.

Moreover, the study also found a link between the Oxford vaccine and increased risk of arterial clotting and haemorrhage.

This careful analysis of an entire country’s vaccination program, which involved the study of over 2.5m first dose vaccines, has found a small increase in the risk of ITP, clotting and bleeding events following the Oxford-AstraZeneca vaccine. This very small risk is important but needs to be seen within the context of the very clear benefits of the vaccines and potentially higher risks of these outcomes in those who develop Covid-19.

Professor Aziz Sheikh, study lead

Interestingly, the team did not find an increased risk of ITP, blood clots, and bleeding with the Pfizer vaccine. Furthermore, they could not establish a link between CVT and vaccines due to the low number of cases among vaccinated people.

The authors of the study suggest that health authorities make recipients of the Oxford vaccine aware of the low risk. However, it should be reinforced that the risk of ITP, blood clots, and bleeding from COVID-19 is much higher than with the vaccine.


Simpson, C.R. et al. First-dose ChAdOx1 and BNT162b2 COVID-19 vaccines and thrombocytopenic, thromboembolic and hemorrhagic events in Scotland. Nat Med (2021).


Please enter your comment!
Please enter your name here