Several studies on Covaxin have demonstrated an excellent safety track record, said Bharat Biotech on 16 May, after a study raised concerns of stroke and Guillain-Barre syndrome (a rare autoimmune disorder that affects the nerves) a year after taking the COVID-19 vaccine.

The study, led by Banaras Hindu University (BHU), claimed that Covaxin raised the rare risk of stroke, and Guillain-Barre syndrome, among others.

"Several studies have been executed on the safety of Covaxin, and published in peer-reviewed journals, demonstrating an excellent safety track record," the Hyderabad-based drug maker said in a statement.

The company noted that for such a study in safety to be effective, informative and to avoid investigator bias: "AESI (adverse events of special interest) safety profile of the subjects before participation in the study has to be kept in mind.

"Comparison of the safety profile of non-vaccinated subjects during the course of the study, comparison of the safety profile of subjects who received other vaccines during the course of the study, and all study participants should be followed during the course of the study, instead of only a subset," Bharat Biotech added.

Recently, AstraZeneca admitted in the UK High Court about the rare risk of blood clot disorder due to its COVID vaccine called Thrombotic Thrombocytopenic Syndrome (TTS) -- a blood clot disorder.

Meanwhile, AstraZeneca's vaccine, made in collaboration with Oxford University, has also been found by researchers to raise the risk of vaccine-induced immune thrombocytopenia and thrombosis (VITT) -- a rare but fatal blood clotting disorder.