4 min readNew DelhiMay 1, 2024 03:50 PM IST
First published on: Apr 30, 2024 at 12:31 PM IST
According to a report by The Telegraph, AstraZeneca, the company behind the Covishield vaccine, has acknowledged in court documents for the first time that the vaccine may lead to a rare side effect. It said, “It is admitted that the AZ vaccine can, in very rare cases, cause TTS. The causal mechanism is not known.” This marks a notable reversal that could lead to a multi-million pound legal payout.
According to the report, the company is being sued in a class action over claims that its vaccine can cause a health issue called Thrombosis with Thrombocytopenia Syndrome (TTS). This condition leads to blood clots forming in the body and a decrease in the number of platelets in the blood. Covishield, developed by AstraZeneca and Oxford University, was widely used during the COVID-19 pandemic, including in India where it was produced by the Serum Institute.
What is TTS?
Dr Jagadish J Hiremath, a public health intellectual, elaborates, “Thrombosis with Thrombocytopenia Syndrome (TTS) is a rare condition characterised by the formation of blood clots (thrombosis) in blood vessels and a low number of blood platelets (thrombocytopenia). It has been observed as an extremely rare adverse effect associated with certain COVID-19 vaccines, notably those that use adenovirus vectors, like the AstraZeneca vaccine (Covishield).”
The exact mechanism by which TTS occurs following vaccination with Covishield isn’t fully understood. However, he adds, it is hypothesised that the vaccine may trigger an immune response that leads to platelet activation and the formation of blood clots, which is similar to autoimmune heparin-induced thrombocytopenia.
“This differs from non-vaccine related thrombosis where factors such as surgery, smoking, or obesity might trigger thrombosis without the immune-mediated platelet activation seen in TTS,” he says.
Who is at risk?
While TTS is exceedingly rare, according to Dr Hiremath, certain factors might predispose individuals to this condition, such as age, gender (more common in younger women), and possibly genetic factors.
Health providers are encouraged to monitor for symptoms of TTS, especially in individuals more at risk, to manage and treat the condition promptly.
Thrombosis with Thrombocytopenia Syndrome (TTS) is a condition that leads to blood clots forming in the body and a decrease in the number of platelets in the blood. (Source: Freepik)
Clinical presentation and symptoms of TTS
He informs, “TTS typically presents symptoms like severe headache, blurred vision, chest pain, leg swelling, persistent abdominal pain, and shortness of breath appearing within a few weeks after vaccination.”
Early detection and treatment are crucial for recovery, thus both healthcare providers and patients are advised to be vigilant for these symptoms.
Implications of AstraZeneca’s admission for vaccine safety monitoring and regulatory practices
“AstraZeneca’s acknowledgment of the link between Covishield and TTS may prompt enhanced safety monitoring and regulatory oversight for vaccines,” Dr Hiremath believes.
This development, he says, might affect public trust in vaccines, emphasising the need for transparent communication and robust vaccine surveillance systems to maintain public confidence in vaccination programs worldwide.
Should Indians be concerned?
Indians need to be aware but not necessarily alarmed about this report, he assures.
“Given the rarity of TTS, the benefits of the Covishield vaccine in preventing COVID-19, with its potentially severe outcomes, generally outweigh the risks of this rare side effect,” he explains.
Continuous monitoring and prompt medical attention for symptoms are recommended strategies for managing the risk.
The exact mechanism linking vaccines to neuropathy is not fully understood. (Source: Freepik) 
Thrombosis with Thrombocytopenia Syndrome (TTS) is a condition that leads to blood clots forming in the body and a decrease in the number of platelets in the blood. (Source: Freepik)
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