German and Austrian researchers found that the blood clots in those vaccinated with Covishield are similar to what is known as heparin-induced thrombocytopenia. whether rare blood clots have formed after vaccination with the AstraZeneca vaccine — known as Covishield in India — becomes apparent within 5 to 20 days, and the widely available ELISA tests can be used to check if a person is at risk of such life-threatening blood clots.