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The life-threatening condition known as thrombosis with thrombocytopenia syndrome (TTS) has been seen in a very small number of people after receiving the adenovirus-based Johnson & Johnson or Oxford-AstraZeneca vaccines, but the risk between different COVID-19 vaccines compared to one another remained unclear.
In a new study published in the BMJ, DPhil student Xintong Li and an international team of researchers used routinely collected health data from five European countries and the USA to produced risk estimates. They found that people who received a first dose of the Oxford-AstraZeneca vaccine ChAdOx1 had a 30% increased risk of thrombocytopenia versus people who received a first dose of the mRNA-based BioNTech, Pfizer vaccine. Although requiring further study, they also saw an increased risk of TTS from the Johnson & Johnson Ad26.COV2 vaccine.