COVID-19 Vaccines and Blood Clots 

COVID-19 Vaccines and Blood Clots 

Part of: GS Prelims and GS – III – Sci & tech 

In news

• Reports of rare blood clots occurring after COVID-19 vaccination have led some countries to limit the usage of AstraZeneca’s vaccine for certain categories of people, while other countries have paused the administration.

Key takeaways 

• An adverse effect following immunisation with the AstraZeneca jab is not merely blood clots in large vessels, but also a low platelet count.
• The effect is similar to heparin-induced thrombocytopenia (HIT), where heparin, which is used to clear clots, actually causes blood clots and a fall in the platelet count.
• The heparin combines with platelet factor 4 to form a complex. 
• This immune complex induces an abnormal immune response, in which antibodies are generated against the complex.
• This antibody-platelet factor 4-heparin immune complex binds to platelets and activates them. 
• The platelets form clots everywhere. 
• The low platelet count is because the platelets are used up.
• A similar process seems to follow vaccination, except there is no heparin trigger.
• Scientists are still trying to establish a clinical definition for this adverse effect.