A new pre-print from a team at the University of Oxford has found that the AstraZeneca vaccine, which is being restricted or banned around the world over links to blood clots, does not appear to cause the rare side effect at a much greater rate than the Pfizer or Moderna vaccines. However, on the basis of current reporting rates, the same complications are many times more likely to be caused by the disease itself, they say. The Independent has the story.
The risk of developing a rare brain clot from COVID-19 is about eight times greater than from the AstraZeneca–Oxford vaccine, according to a new study.
Researchers at the University of Oxford, who are not linked to the vaccine, also found that people infected with coronavirus are “manyfold times” more likely than normal to develop the rare clotting disorder, known as cerebral venous thrombosis (CVT), where blood clots in the veins that run from the brain.
“There’s no doubt that Covid is a much greater risk of this [condition] than any of the vaccines,” said Professor Paul Harrison, a co-author of the study.
The research, which has yet to be peer-reviewed, drew comparisons between more than 500,000 COVID-19 patients in the US and 34 million people in Europe who have received the AstraZeneca vaccine, as well as the background level of CVT in the general population.
For COVID-19, the incidence rate of CVT stands at 39 cases per one million people, the study showed. But for a million people vaccinated with the AstraZeneca jab, there will be just five cases of CVT over a two-week period. …
The study also suggested that four cases of CVT are likely to occur in one million people vaccinated with either the Moderna or Pfizer/BioNTech jab. However, the scientists warned that the data on this is too thin to establish any firm conclusions.
The researchers acknowledge a number of limitations in their research.
The scientists warned that all comparisons must be interpreted cautiously since data are still accruing and drawn from different sources. They added that their research was unable to determine the relative risk of developing CVT after vaccination due to uncertainty around the baseline rate for this condition.
Nor did the study address the incidence rate of thrombocytopenia in COVID-19 patients and people who had been vaccinated. This condition, where a patient presents abnormally low levels of platelets, has been detected alongside CVT in the cases of concern reported to date. …
The Oxford researchers drew their COVID-19 patient data from a US-based electronic health records network which had recently been used by the team to show the neurological and psychiatric consequences of coronavirus.
This database, which is made up of a total of 81 million US patients, provided clear detail on CVT cases that had been detected among people infected with coronavirus, the experts said – though they acknowledged there may be under-reporting of the condition in medical records.
As for the incidence rate of CVT among people vaccinated with the AstraZeneca jab, this was taken from the European Medicines Agency’s database, which covered more than 34 million individuals at the time of publication.
A further observation is that the COVID-19 patients in the study are drawn from a “federated electronic health records network recording anonymised data from healthcare organisations, primarily in the USA”. This suggests they are hospital patients, or at least those who have sought medical assistance, and so are not representative of all Covid infections but only the more serious. This contrasts to the vaccinated group, which is the healthy population as a whole, albeit with more vulnerable groups often vaccinated first. This may skew the comparison considerably, making blood clots among those infected with Covid appear much more common than they are.
How will regulators respond, having restricted one vaccine over this issue (and increasingly the Johnson & Johnson one as well), will they not have to be consistent? Will they remove the restrictions from AZ and J&J, or apply them equally to the other two, or somehow justify the discrepancy? Will be interesting to watch this play out.