Delta variant: Expert on vaccines’ impact on transmissibility
The argument in favour of getting vaccinated against COVID-19 is unassailable. Studies continue to attest to the protective benefits of the vaccines and a new study published in the British Medical Journal is no exception. Researchers in the study compared the AstraZeneca and Pfizer vaccines with the risks from COVID-19.
Among the key findings were an association between those vaccinated with the Pfizer jab and an increased risk of stroke, but the risk was more than 10 times greater in those with the virus.
Professor Julia Hippisley-Cox, professor of clinical epidemiology and general practice at the University of Oxford, said the increased risk they detected was only for a short time after vaccine, compared to a longer period if infected with the virus.
She said: “For stroke, with Pfizer it was just 15 to 21 days after vaccination that there was an increased risk.”
The researchers’ findings also suggest the risk of thrombocytopenia – a condition where the patient has a low count of cells, known as platelets, that help the blood clot – in someone with coronavirus is almost nine times higher than in someone who has had one dose of the AstraZeneca jab.
Pfizer effects: BMJ study finds stroke risk increases immediately after jab
This should further quell fears about the risk of developing blood clots after receiving the AstraZeneca jab.
To arrive at this conclusion, the researchers looked at more than 29 million people aged 16 or older who had a first dose of either vaccine in England between December and April.
Professor Aziz Sheikh, one of those involved in the study, said the increased risk of thrombocytopenia seen in their work is similar to other commonly used vaccines in the UK, such as the flu jab.
They estimated that in 10 million people vaccinated with the AstraZeneca jab, there would be 107 additional cases of thrombocytopenia in the 28 days post-vaccination, compared with 934 in people with the virus.
The BMJ paper stated that per 10 million people jabbed with AstraZeneca, there were an estimated seven additional cases of CVST, while there were 20 in people with COVID-19.
For blood clotting in a vein (venous thromboembolism), they estimated some 66 excess events per 10 million people vaccinated with AstraZeneca, compared with around 12,614 excess events in those with Covid.
There were no associations with blood clots in an artery (arterial thromboembolism) for either vaccine, but there were some 5,000 excess events per 10 million people infected with Covid, they said.
In regards to the risk of stroke, there were an estimated 143 extra cases of ischaemic stroke per 10 million people with Pfizer, compared with 1,699 cases in those with COVID-19.
Vaccine blood clot risk: Risk of clots nine times greater in people with Covid
Researchers found no association for AstraZeneca with stroke risk, or Pfizer with increased risk of thrombocytopenia.
Prof Sheikh, director of the Usher Institute at the University of Edinburgh, said the study is important in “contextualising” safety findings “when compared with the risks if you get the infection” which he said other studies have not done to date.
Prof Hippisley-Cox said: “There’s always some unanticipated effects with any medicine and I think that this study design is the most robust way of looking at detecting these events and putting them in some context.”
Dr Martina Patone, a statistician at the University of Oxford, added: “We looked at hospital admission or deaths due to blood clots within 28 days of having either vaccine, and what we found is an increased risk with both vaccines, but also that the risk of blood clots is much higher if you caught COVID-19, either before or after vaccination.”
Flu jab: Common flu jab side effects
The findings should not come as a surprise.
Hundreds of millions of people have had a coronavirus (COVID-19) vaccine and the safety of the vaccines continues to be monitored.
Reports of serious side effects are very rare.
What’s more, COVID-19 vaccines have to go through several stages of clinical trials before they can be approved for use.
Clinical trials are where a vaccine or medicine is tested on volunteers to make sure it works and is safe.
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