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WEDNESDAY, September 28, 2022
Vaxzevria showed no increased incidence of thrombosis with thrombocytopenia after second dose

Vaxzevria showed no increased incidence of thrombosis with thrombocytopenia after second dose

FRIDAY, July 30, 2021

Rates of the very rare clotting disorder, thrombosis with thrombocytopenia syndrome (TTS), following a second dose of Vaxzevria are comparable to the background rate in an unvaccinated population.

The data, published in The Lancet today, demonstrated the estimated rate of TTS following a second dose of Vaxzevria was 2.3 per million vaccinees, comparable to the background rate observed in an unvaccinated population. It was 8.1 per million vaccinees after the first dose. The rate after the second dose is comparable to background rates observed in unvaccinated populations.

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.”

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. Reported cases of TTS globally were included up to the cut-off date of April 30 occurring within 14 days of administration of the first or second dose of Vaxzevria.

The results are in line with recent reports in the Medicines and Healthcare products Regulatory Agency (MHRA) Yellow Card Report, the UK system for collecting and monitoring information on safety concerns, which also show low rates of TTS after a second dose.


No specific risk factors or definitive cause for TTS following COVID-19 vaccination have been identified and AstraZeneca continues to perform and support ongoing investigations of potential mechanisms. Furthermore, these very rare events can be avoided when symptoms are identified and treated appropriately.