Infection by the virus that causes Covid-19 is about 100 times more likely to cause blood clots in the brain than any Covid vaccine on the market, according to a new study carried out by Oxford University.
The occurrence of blood clots following vaccination with the AstraZeneca (AZ) vaccine and more recently the Johnson & Johnson vaccine has led to the vaccines being suspended in some countries while the phenomenon was investigated.
The AZ vaccine was developed in conjunction with Oxford University, but there is no suggestion there is any connection between that part of the university and the departments responsible for the latest research.
Specifically, those are Professor Paul Harrison and Dr Maxime Taquet from the department of psychiatry and the NIHR Oxford Health Biomedical Research Centre.
The study looked at one specific type of blood clotting known as cerebral venous thrombosis (CVT), where the clot blocks the veins taking blood away from the brain, to go back to the lungs to be oxygenated.
Symptoms range from severe headache to the symptoms of a stroke, and treatment is by medication or in severe case surgery to relieve pressure inside the skull.
The study looked at 500,000 Covid-19 patients, and found an incidence of CVT of 39 in a million. In 480,000 people having received the vaccines from Moderna or Pfizer, the rate was four per million. For the AZ vaccine, the rate rose to five per million.
In short, the risk of CVT caused by a vaccine was roughly 8-10 times lower than becoming infected with Covid-19.
‘There are concerns about possible associations between vaccines, and CVT, causing governments and regulators to restrict the use of certain vaccines,” said professor of psychiatry Paul Harrison. “Yet, one key question remained unknown: What is the risk of CVT following a diagnosis of Covid-19?”
“‘We’ve reached two important conclusions. Firstly, Covid-19 markedly increases the risk of CVT, adding to the list of blood clotting problems this infection causes. Secondly, the Covid-19 risk is higher than we see with the current vaccines, even for those under 30; something that should be taken into account when considering the balances between risks and benefits for vaccination.”