Risk of blood clot higher after COVID-19 than vaccine

LONDON: The risk of developing a blood clot after having COVID-19 is eight times higher than after being given the Oxford-AstraZeneca vaccine, according to a study by Oxford University, foreign media reported.

Cerebral venous thrombosis (CVT) occurred in 39 in a million COVID-19 patients, compared with about five in a million people given the AstraZeneca jab.

In the study of over 500,000 coronavirus patients, the risk was reported to be around 100 times higher than normal after infection. Numerous countries have limited use of the vaccine to certain age groups or paused its rollout following reports of very rare cases of blood clots. The UK's medical regulator has said the vaccine is still safe and effective but has limited its use in those under 30 as this age group is less at risk of becoming seriously ill with coronavirus.

However, the Oxford study suggested around a third (30%) of the CVT reports after COVID-19 infection were in people under 30.

Scientists have said the technology used in the Oxford-AstraZeneca vaccine, harnessing an adenovirus, has been linked to a slightly increased risk of blood clots.

In over 480,000 people who received the Pfizer or Modernavaccines, which use mRNA technology instead, CVT occurred in about four in a million people.

The risk of developing CVT after taking either of these vaccines is about 10 times lower than after being infected with coronavirus, the study suggests. But the researchers said comparisons should be interpreted with caution because data is still being gathered.

Meanwhile, Dr. Purvi Parikh also told CNBC that the risk of developing blood clots from COVID-19 is greater than the apparent likelihood of developing them from Johnson & Johnson’s coronavirus vaccine.

Parikh, a New York-based allergist and immunologist, has worked as an investigator for other COVID vaccine trials, including Pfizer.

Looking at the FDA recommendation to pause use of J&J’s one-shot vaccine through that prism, Parikh said the temporary halt indicates that regulators’ “safety checks and balances are working.”

“For now, I would be careful with any of these conspiracy theories and again with the panic,” said Parikh, a clinical assistant professor in the Department of Medicine at NYU Grossman School of Medicine.

“You’re much more likely to clot from the real COVID-19 virus, which is about 1 in 20 people hospitalised or even 1 in 100 recovering at home. That’s far more likely,” she added, citing data from industry group Thrombosis Canada.

Meanwhile, Denmark will no longer offer the AstraZeneca vaccine as part of its immunisation programme, becoming the first country to drop the vaccine over suspected rare but serious side-effects.

The move comes in spite of strong recommendations from the World Health Organization and European medicines watchdog to continue using the inoculation, as the benefits far outweigh any potential risk.

“Denmark’s vaccination campaign will go ahead without the AstraZeneca vaccine,” the director of the Danish health authority, Søren Brostrøm, told a press conference. Neighbouring Sweden has said it plans to pause its own roll-out of a second vaccine, produced by Johnson & Johnson, which has also been linked to rare blood clots. Finland also announced that it would continue to limit the AstraZeneca vaccine to people aged 65 and over.