Cerebral venous thrombosis has been a significant complication of COVID-19 at a rate far higher than seen after vaccination, British researchers have reported.
The finding highlights the benefits of vaccination – but will also raise questions about whether there is a link between the two phenomena.
It came as recorded deaths from the virus in Europe passed a million amid delays in vaccination programmes in many countries.
The Oxford University researchers studied 500,000 COVID-19 patients and found the condition occurring 39 times in a million – about a hundred times more than normal. 30% of cases occurred in people under the age of 30.
Compared with the incidence in people who have been recently vaccinated, the risk was also significantly increased but not by as much. Compared with mRNA vaccination it was ten times increased and compared with the Oxford vaccine it is eight times increased, according to the study.
The researchers said there was a similar pattern for portal vein thrombosis.
Researcher Professor Paul Harrison said: “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 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.”
Fellow researcher Dr Maxime Taquet added: “It’s important to note that this data should be interpreted cautiously, especially since the data on the Oxford-AstraZeneca vaccine come from UK MHRA monitoring, whereas the other data uses the TriNetX electronic health records network. However, the signals that COVID-19 is linked to CVT, as well as portal vein thrombosis – a clotting disorder of the liver – is clear, and one we should take note of.”
The World Health Organisation yesterday backed the Oxford findings, warning that Europe faces a “serious” situation with 1.6 million new cases recorded weekly.
Regional director Dr Hans Kluge said: “For now, the risk of suffering blood clots is much higher for someone with COVID-19 than for someone who has taken the AstraZeneca vaccine.
“Let there be no doubt about it, the AstraZeneca vaccine is effective in reducing COVID-19 hospitalisation and preventing deaths. WHO recommends it to all eligible adults to gain protection from the SARS-CoV-2 virus, as quickly as possible.”
He said: “Hospitalisation remains at high levels, with continued reports of intensive care capacity having been exceeded, from all parts of the Region – also in Greece. This April, COVID-19 admissions to hospitals and intensive care in France reached the highest levels since this time last year.
“There are early signs that transmission may be slowing across several countries. Let me be clear, early signs of decline are not equal to low rates of transmission. Transmission must be driven down to low rates and kept low, by harnessing our energy and resilience to beat the virus.”
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