Covishield, developed by AstraZeneca and Oxford University during the pandemic, was produced by the Serum Institute of India (SII) and was administered in the country as part of the innoculation drive against Covid-19.

AstraZeneca made the admission in the action lawsuit it is in the United Kingdom over claims that its vaccine caused deaths and severe injuries in several cases. Victims in as many as 51 cases in the UK High Court are seeking damages up to 100 million pounds.

Jamie Scott, the first complainant in the case, made allegations that he was administered the vaccine in April 2021, which he said led to a permanent brain injury after a blood clot, according to a report in The Telegraph. This has prevented him from working and the hospital even told his wife thrice that he's going to die, he claimed.

While AstraZeneca contested the claims, it admitted in one of the court documents in February that Covishield can "in very rare cases, cause TTS", the report said.

TTS - Thrombosis with Thrombocytopenia Syndrome - causes blood clots and a low blood platelet count in humans.

According to National Library of Medicine, thrombosis with thrombocytopenia syndrome (TTS), including vaccine-induced immune thrombotic thrombocytopenia (VITT), "is an extremely rare adverse effect, mostly seen after initial vaccination with the viral vector-based AstraZeneca-Oxford COVID-19 vaccine. It is characterised by mild to severe thrombocytopenia and venous or arterial thrombosis."

"It is admitted that the AZ vaccine can, in very rare cases, cause TTS. The causal mechanism is not known...Further, TTS can also occur in the absence of the AZ vaccine (or any vaccine). Causation in any individual case will be a matter for expert evidence," The Telegraph report quoted AstraZeneca as saying.

AstraZeneca reportedly made its admission in a legal defence to complainant Jamie Scott's claim, which may lead to payouts to the victims and their relatives.

The latest admission by AstraZeneca also contradicts its 2023 stand wherein it refused to accept that TTS is caused by the vaccine at a generic level."

AstraZeneca has, however, denied the lawyers' claims that the vaccine is "defective" and its efficacy "vastly overstated".