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Study shows AZ’s COVID-19 vaccine did not increase rate of rare blood clots after second dose

Data published in The Lancet has demonstrated that AstraZeneca’s COVID-19 jab Vaxzevria (formerly AZD1222) does not increase the rate of rare blood clots after the second dose.

The analysis was conducted using AstraZeneca’s global safety database, which captures all spontaneously reported adverse events from real-world use of its medicines and vaccines worldwide.

It showed that rates of the very rare clotting disorder, thrombosis with thrombocytopenia syndrome (TTS), following a second dose of Vaxzevria was 2.3 per million vaccinees, comparable to the background rate in an unvaccinated population. It was 8.1 per million vaccinees after the first dose.1

More than 800 million doses of COVID-19 Vaccine AstraZeneca have been supplied to more than 170 countries worldwide, including more than 100 countries through the COVAX Facility.

Sir Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, said: “Vaxzevria is effective against all severities of COVID-19 and it plays a critical role in combatting the pandemic. Unless TTS was identified after the first dose, these results support the administration of the two-dose schedule of Vaxzevria, as indicated, to help provide protection against COVID-19 including against rising variants of concern.”


1. Bhuyan P., et al., (2021) Thrombosis with thrombocytopenia after second AZD1222 dose: a global safety database analysis of rare cases. The Lancet. Published Online: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01693-7/fulltext

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Emma Cooper
Emma is Digital Editor at Pf.


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