COVID-19 and the VITT effect: Vaccination and risk of thrombocytopenia

COVID-19 and the VITT effect: Vaccination and risk of thrombocytopenia

This is a large analysis, based on health data from 5 European countries and the United States, which reveals “trends” of increased risk of clots, after a first dose of the Oxford-AstraZeneca vaccine, Janssen/Johnson & Johnson vs. Pfizer-BioNTech. Although the authors emphasize that the syndrome remains very rare, they nevertheless call for these risks to be taken into account when organizing new vaccination campaigns and developing new vaccines.

Thrombocytopenia syndrome occurs when a person has blood clots (thrombosis) along with a low number of blood platelets (thrombocytopenia). This syndrome is therefore different from more common bleeding disorders such as deep vein thrombosis (DVT) or pulmonary clots (pulmonary embolism).

The condition is still being researched, as a rare side effect of adenovirus-based COVID-19 vaccines:

these “live attenuated” vaccines use a weakened version of the virus to trigger an immune response against the coronavirus.

The study: this international team of researchers compared the risk of thrombocytopenia and thromboembolic events associated with the use of adenovirus-based COVID-19 vaccines with the risk associated with other types of vaccines, based on mRNA. Analysis of health data from more than 10 million adults in France, Germany, the Netherlands, Spain, the United Kingdom and the United States, who have received at least one dose of a COVID vaccine (Oxford-AstraZeneca, Pfizer-BioNTech, Moderna or Janssen/Johnson & Johnson) from December 2020 to mid-2021, reveals that:

  • 862 events of thrombocytopenia were noted in people who received the first dose of the Oxford-AstraZeneca vaccine;
  • 520 events after a first dose of the Pfizer-BioNTech vaccine;
  • There is a 30% increased risk of thrombocytopenia after a first dose of Oxford-AstraZeneca vs Pfizer-BioNTech, ie an absolute risk difference of 8.21 per 100,000 recipients;
  • an increased risk, although not statistically significant, of venous thrombosis with thrombocytopenia is observed after a first dose of Janssen/Johnson & Johnson vs Pfizer-BioNTech vaccine. This result should nevertheless be confirmed by other studies;
  • no difference in risk of thrombocytopenia is observed after a second dose of the Oxford-AstraZeneca vaccine vs a second dose of the Pfizer-BioNTech vaccine;
  • no increased risk of thrombocytopenia is also noted after the Janssen/Johnson & Johnson vaccine vs a first dose of Pfizer-BioNTech.

If the study is observational, the disease is rare, and some vaccination records are incomplete, it is nevertheless a well-designed study which makes it possible to compare the available vaccines with each other and whose results remain consistent, even after additional analyses. , say the researchers:

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

#COVID19 #VITT #effect #Vaccination #risk #thrombocytopenia

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