The risk of developing a blood clot after contracting the coronavirus is eight times higher than after receiving the Oxford-AstraZeneca vaccine, according to a study by Oxford University.
In the study of over 500,000 COVID-19 patients, cerebral venous thrombosis (CVT) occurred in 39 in a million COVID-19 patients, compared with about five in a million people given the Oxford-AstraZeneca jab.
CVT occurred in 4 in a million people given a COVID-19 mRNA vaccine (Pfizer or Moderna).
The study authors counted the number of CVT cases diagnosed in the two weeks following diagnosis of COVID-19, or after the first dose of a vaccine.
They found that CVT is more common after COVID-19 than in any of the comparison groups, with 30% of these cases occurring in the under 30s.
Compared to the current COVID-19 vaccines, this risk is between 8-10 times higher, and around 100 times higher than normal after infection.
Compared to the mRNA vaccines, the risk of a CVT from COVID-19 is about 10 times greater.
Compared to the AZ-Oxford vaccine, the risk of a CVT from COVID-19 is about 8 times greater.
Professor Paul Harrison, who led the study alongside Dr Maxime Taquet from Oxford University’s Department of Psychiatry and the NIHR Oxford Health Biomedical Research Centre said: ‘There are concerns about possible associations between vaccines, and CVT, causing governments and regulators to restrict the use of certain vaccines.”
“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."
Prof Harrison said this was "something that should be taken into account when considering the balances between risks and benefits for vaccination."
A spokesperson for AstraZeneca said the analysis adds “further evidence to help understand the relevance of these extremely rare events as we continue to work to understand possible mechanisms.”
Earlier today, the Tánaiste warned that anyone who refuses an AstraZeneca vaccine will have to wait until the entire population is vaccinated to be offered an alternative.