No extra risk of blood clot after second shot of AstraZeneca’s COVID-19 vaccine, says Lancet study

TTS (thrombosis with thrombocytopenia syndrome) is an extremely rare syndrome occurred when a person has blood clots along with low blood platelets.

According to a study led and funded by AstraZeneca plc, the UK-based drugmaker’s coronavirus vaccine is linked with a small risk of rare blood clots after the first shot but no extra risk after the second dose.

On July 27, the research published in The Lancet stated that after receiving both doses of the AstraZeneca COVID-19 vaccine, the rates of a very rare clotting disorder called thrombosis with thrombocytopenia syndrome (TTS), are comparable to those among people who are not yet inoculated. As per the authors, TTS’ estimated rate following a second shot of AstraZeneca COVID-19 vaccine was 2.3 per million vaccinated individuals. The rate stood at 8.1 million vaccinated people after the first dose.


After receiving the first shot of AstraZeneca’s vaccine, rare cases of the syndrome were reported in India, where Serum Institute of India (SII) is in charge of manufacturing the vaccine as Covishield. As a result, several countries across the world restricted or even stopped the usage of this vaccine.

The British-Swedish pharmaceutical company stated, “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.” It continued saying that these “rare events” are avoidable if symptoms are identified and treated appropriately.

TTS is also referred to as vaccine-induced immune thrombotic thrombocytopenia (VITT).