AstraZeneca recently admitted a possible link between its vaccine and Thrombosis with Thrombocytopenia Syndrome (TTS) in very rare cases.


  • Global pharmaceutical giant AstraZeneca has said that its AZD1222 vaccine against COVID-19 could cause Thrombosis with Thrombocytopenia Syndrome (TTS), which can lead to low platelet counts and formation of blood clots in “very rare” cases. 
  • During the COVID-19 pandemic, AstraZeneca licensed its vaccine formula to the Pune-based vaccine manufacturer Serum Institute of India (SII) to produce Covishield.
  • Over 175 crore Covishield doses have been administered in India.

Key Points:

  • AstraZeneca’s admission came in response to a lawsuit in the UK regarding health issues following vaccination.
  • Previous Concerns: 
  • Similar concerns were raised in 2021, leading to temporary pauses in vaccination in some European countries.
  • The Indian government issued a cautionary fact sheet for Covishield in case of low platelet count.
  • The World Health Organization (WHO) acknowledged TTS cases but considered the risk very low.

Reported Cases in India: 

  • 26 potential thromboembolic events were reported in May 2021 (out of initial doses administered).
  • At least 36 TTS cases were confirmed by the government committee (mostly in 2021, the first year of vaccination).
  • 18 deaths were reported among these confirmed TTS cases.

Key facts:

  • Scientific studies suggest a lower risk of blood clots in South and Southeast Asian descent compared to Europeans.
  • In 2023, WHO classified vaccine-induced TTS (VITT) within the TTS category.

Government Stance:

  • The risk of blood clots with Covishield is minuscule at 0.61 cases per million doses.
  • Covishield’s benefits in preventing COVID-19 infections and deaths outweigh the risks.
  • No TTS cases were reported with Covaxin (indigenous Indian vaccine).

Thrombosis with Thrombocytopenia Syndrome (TTS)

TTS is characterized by blood clots (thrombosis) combined with low levels of platelets 

  • (thrombocytopenia), which are necessary for blood clotting. 
  • Thrombosis can obstruct blood flow in veins and arteries, with complications varying depending on its location. Among the most severe issues are stroke, heart attack, and significant respiratory difficulties.

Symptoms of TTS:

  • Breathlessness
  • Chest or limb pain
  • Pinhead-sized red spots or bruising of the skin beyond the injection site
  • Headaches
  • Numbness in body parts

Comorbidity Link:

While TTS can occur in anyone who receives certain vaccines, some pre-existing medical conditions might increase the risk. These potential comorbidities include:

  • Autoimmune diseases: Conditions where the immune system attacks healthy tissues (e.g., lupus, rheumatoid arthritis)
  • Blood clotting disorders: Conditions that make blood clot more easily (e.g., deep vein thrombosis, pulmonary embolism)
  • Cancer: Certain cancers can increase the risk of blood clots.

Is there any danger now?

Experts say that most TTS events occurred within the first 21 days following vaccination, and only a minuscule percentage of events had a fatal outcome. It has been more than two years of getting vaccinated, and it has no long-term effects. Thus, they reassure that no medication is necessary at this time.

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