The Serum Institute of India on Sunday filed a Rs 100 crore defamation suit against a Chennai-based volunteer who took part in their coronavirus vaccine trial and alleged that it triggered an adverse reaction, including neurological impairment.

Serum Institute has partnered with drug manufacturer AstraZeneca and the University of Oxford to produce the Covishield vaccine in the country. The vaccine is seen as a possible option for many developing countries because of its cheaper price and ability to be transported and stored at normal temperatures.

The volunteer had sent a legal notice on November 21 and sued Serum Institute for Rs 5 crore. However, the company denied the allegations and called them “malicious” and “misconceived”. In a statement, a Serum Institute spokesperson said that while they sympathised with the volunteer’s medical condition, there was “absolutely no correlation with the vaccine trial and the medical condition of the volunteer”.

“The claim is malicious because the volunteer was specifically informed by the medical team that the complications he suffered were independent of the vaccine trial he underwent,” the statement said. “The volunteer is falsely laying the blame for his medical problems on the Covid vaccine trial. Inspite of specifically being made aware of the same, he still chose to go public and malign the reputation of the company.”

The statement claimed the man was spreading “malicious information” with “an oblique pecuniary” motive. “The Serum Institute of India, will seek damages in excess of [Rs] 100 crore for the same and will defend such malicious claims,” it added.

The participant was administered a dose of the vaccine at Chennai’s Sri Ramachandra Institute of Higher Education and Research on October 1. Copies of his legal notice have also been sent to the Chief Executive of AstraZeneca in the United Kingdom, chief investigator of the Oxford trials and vice-chancellor of Ramachandra Institute.

The man has demanded that the vaccine trial be immediately halted and all plans for its “manufacture and distribution” be suspended, failing which legal action would be taken. According to the legal notice, there was a total “behavioural change” in the participant and he seemed unaware of his surroundings.

“The trauma he underwent after taking it clearly proves that the vaccine was not safe as made out to be and all the stakeholders were trying to hide the adverse effect that the vaccine has had on him,” the notice said. “He has gone through extreme sufferings, both biologically and psychologically. The vaccine had led to a virtual neurological breakdown in him.”

It also mentioned that no public disclosure about the incident was made even after the participant reported his condition. It contrasted this response with the Serum Institute’s decision to suspend trials in India after AstraZeneca paused its clinical trials in September because of “an unexplained illness” in a participant in the study.

The new controversy came at a time when doubts have been already raised about the vaccine after AstraZeneca and Oxford University acknowledged a manufacturing error. Based on the strength at which the doses were given, the vaccine appeared to be either 90% or 62% effective. The average efficacy, the developers said, was 70% in phase three trials. But questions mounted on why there was such a large variation in the effectiveness of the vaccine at different doses, and on why a smaller dose appeared to produce much better results.