London: A study led by the University of Oxford on Friday noted that a coronavirus infection presents a much higher risk of developing a blood clot than the first dose of Oxford/ AstraZeneca or Pfizer/ BioNTech jab. The research used findings from more than 29 million people who were vaccinated with the first dose of either vaccine between December 2020 and April 2021. The findings showed that although there was an increased risk of developing blood clots after receiving the first dose of either vaccine, it was much greater in someone who had tested positive for Covid-19 caused by the SARS-CoV-2 virus.
The study covered thrombocytopenia (a condition with low platelet counts) and thromboembolic events following vaccination for Covid 19. These are the same events that had led to the restricted use of the vaccine in several countries. The Oxford/ AstraZeneca vaccine is produced and administered in India as Covishield.
The study concluded that for short time intervals after the first dose, there are increased risks of some haematological and vascular adverse events with both of these vaccines, which may lead to hospitalization or death. Other outcomes studied were cerebral venous sinus thrombosis (CVST), ischemic stroke, myocardial infarction and other rare arterial thrombotic events.
All coronavirus vaccines currently in use have been tested in randomized clinical trials, which are unlikely to be large enough to detect infrequent adverse events. When rare events are uncovered, the regulators perform a risk-benefit analysis of the medicine to compare the risks of the adverse events if vaccinated versus the benefits of avoiding the disease.
Co-author Aziz Sheikh, who is a Professor of Primary Care Research and Development and Director of the Usher Institute at the University of Edinburgh, said, "On balance, this analysis therefore clearly underscores the importance of getting vaccinated to reduce the risk of these clotting and bleeding outcomes in individuals, and because of the substantial public health benefit that Covid 19 vaccinations offer."