Scientists uncover more data on blood clotting side effects of Covid jab

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Scientists have uncovered more knowledge about the risk of developing a very rare blood clotting condition after vaccination against COVID-19, a study has found. Based on health data from five European countries and the United States, the study shows an increased risk of the disease, called thrombosis with thrombocytopenia syndrome (STT), after the first dose of the Oxford-Astrazeneca vaccine (identical to Covishield in formulation).



The study, published in the British Medical Journal (BMJ), also shows a trend of increased risk after the Janssen/Johnson & Johnson vaccine, compared to the Pfizer-BioNTech vaccine.

The researchers stressed that the syndrome is very rare, but said the observed risks “should be considered when planning new vaccination campaigns and future vaccine development.”

TTTS occurs when a person has blood clots (thrombosis) along with a low number of blood platelets (thrombocytopenia). According to the study, it is very rare and different from general clotting conditions like deep vein thrombosis (DVT) or lung clots (pulmonary embolism).

TTS is currently being investigated as a rare side effect of adenovirus-based Covid vaccines, which use a weakened virus to trigger an immune response against the coronavirus, but no clear evidence exists on this. comparative safety of different types of vaccines, according to the study.

To address this knowledge gap, an international team of researchers set out to compare the risk of TTS or thromboembolic events associated with the use of adenovirus-based Covid vaccines with mRNA-based Covid vaccines.

Their conclusions were based on health data collected routinely for more than 10 million adults in France, Germanythe Netherlands, Spain, the United Kingdom and the United States which received at least one dose of a Covid vaccine (Oxford-AstraZeneca, Pfizer-BioNTech, Moderna or Janssen/Johnson & Johnson) from December 2020 mid-2021.

Additionally, to minimize possible errors, participants were matched by researchers by age and gender and a range of other potentially influential factors such as pre-existing conditions and medication use were taken into account.

The researchers then compared the rates of thrombosis and thrombosis with thrombocytopenia between adenovirus vaccines (Oxford-AstraZeneca or Janssen/Johnson & Johnson) and mRNA vaccines (Pfizer-BioNTech or Moderna) within 28 days of vaccination.

Overall, 1.3 million first-dose recipients from Oxford-AstraZeneca were matched with 2.1 million Pfizer-BioNTech recipients from Germany and the UK. An additional 7,62,517 people receiving Janssen/Johnson & Johnson have been matched with 2.8 million receiving Pfizer-BioNTech in Germany, Spain and the United States, and the 6,28,164 Janssen/Johnson & Johnson recipients in the United States have been matched with 2.2 million Moderna recipients.

A total of 862 events of thrombocytopenia were found in recipients of the first matched dose of Oxford-AstraZeneca from Germany and the UK, and 520 events after the first dose of Pfizer-BioNTech.

When the data were pooled, the analysis showed a 30% increased risk of thrombocytopenia after the first dose of Oxford-AstraZeneca compared to Pfizer-BioNTech – an absolute risk difference of 8.21 per 100,000 recipients, according to the study.

No differential risk of thrombocytopenia was observed after a second dose of Oxford-AstraZeneca compared to the second dose of Pfizer-BioNTech.

Similarly, no increased risk of thrombocytopenia was noted after Janssen/Johnson & Johnson compared to the first dose of Pfizer-BioNTech.

This is an observational study, and the researchers acknowledge that the rarity of the disease and incomplete vaccination records may have affected the results.

Moreover, scientists cannot rule out the possibility that some of the observed risks are due to other unmeasured and confounding factors.

However, the study claims to be well designed and that it allowed the comparison of available vaccines with each other, rather than with no vaccination, and that the results were consistent after additional analyses, suggesting that they stand up to scrutiny.

“To our knowledge, this is the first multinational analysis of the comparative safety of adenovirus-based vaccines versus mRNA-based Covid-19 vaccines,” the authors said.

“Although these events are very rare, the absolute number of affected patients could become substantial due to the large number of vaccine doses administered worldwide,” they warned.

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