Study illuminates rare blood-clotting risk after COVID-19 vaccine.

BMJ study illuminates the risk of having thrombosis with thrombocytopenia syndrome (TTS) after covid-19 immunisation.

Based on health data from five European nations and the US, the Oxford-AstraZeneca vaccine and Janssen/Johnson & Johnson vaccine had a slightly higher risk of TTS than the Pfizer-BioNTech vaccine.

This illness is rare, but the researchers suggest these concerns “should be addressed when planning further immunisation programmes and future vaccine development.”

Thrombosis and low platelet levels cause TTS (thrombocytopenia). It’s unusual and unlike DVT or lung clots (pulmonary embolism).

TTS is being examined as a rare adverse effect of adenovirus-based covid-19 vaccines, which use a weakened virus to elicit an immune response against coronavirus. No clear information exists on the comparative safety of different vaccinations.

An worldwide team of researchers compared the risk of TTS or thromboembolic events linked with adenovirus-based and mRNA-based COVID-19 vaccinations to fill this information gap.

They used routinely obtained health data from almost 10 million persons in France, Germany, the Netherlands, Spain, the UK, and the US who got at least one dose of a covid-19 vaccination (Oxford-AstraZeneca, Pfizer-BioNTech, Moderna, or Janssen/Johnson & Johnson) from December 2020 to mid-2021.

Participants were matched by age and sex and other criteria like pre-existing illnesses and medication use were considered to reduce error.

The researchers next examined rates of thrombosis and thrombocytopenia between the adenovirus vaccinations (Oxford-AstraZeneca or Janssen/Johnson & Johnson) and the mRNA vaccines (Pfizer-BioNTech or Moderna) 28 days after inoculation.

1.3 million first-dose Oxford-AstraZeneca recipients were matched to 2.1 million German and UK Pfizer-BioNTech recipients.

All 628,164 US Janssen/Johnson & Johnson recipients were matched to 2.2 million Moderna recipients, while 762,517 were matched to 2.8 million Pfizer-BioNTech users in Germany, Spain, and the US.

The matched first-dose Oxford-AstraZeneca recipients from Germany and the UK had 862 thrombocytopenia episodes, and Pfizer-BioNTech had 520.

After a first dosage of Oxford-AstraZeneca, the absolute risk of thrombocytopenia was 8.21 per 100,000 patients, 30% higher than Pfizer-BioNTech.

Janssen/Johnson & Johnson’s initial vaccine dosage increased the risk of venous thrombosis with thrombocytopenia compared to Pfizer-BioNTech, but not statistically significantly. Before drawing conclusions, the researchers stress this finding must be repeated in other investigations.

Oxford-AstraZeneca and Pfizer-BioNTech second doses did not increase thrombocytopenia risk. Janssen/Johnson & Johnson did not raise thrombocytopenia risk compared to Pfizer-initial BioNTech’s dose.

This observational study acknowledges that the condition’s rarity and poor immunisation records may have affected results. They also can’t rule out the potential that unmeasured (confounding) factors contributed to the observed risk.

However, this was a well-designed trial that compared current vaccines against each other rather than to no immunisation, and the results were similar after multiple analyses, suggesting they stand up to examination.


Journal reference:
Li, X., et al. (2022) Comparative risk of thrombosis with thrombocytopenia syndrome or thromboembolic events associated with different covid-19 vaccines: international network cohort study from five European countries and the US. The BMJ.

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