A blood clot that develops after vaccination is called a vaccine-induced thrombosis. The most serious of these clots tend to occur in large veins in the brain and abdomen while the platelets (that would normally be part of the clotting process) drop dangerously low as well. This is called vaccine-induced thrombotic thrombocytopenia. It is an extremely rare condition, but local experts and treatments are available. Chances of developing this condition is extremely rare and the South African Health Products Regulatory Authority (SAHPRA) confirmed that no major safety concerns were identified in the healthcare workers who partook in the Sisonke vaccine trial.

Symptoms include:

  1. Severe headache with blurred vision, vomiting, weakness on one side of the body or difficulty speaking.
  2. Severe abdominal pain that can also be associated with vomiting.
  3. A rash of tiny red spots might occur under the skin around the injection site.
  4. Leg pain or swelling.
  5. Chest pain or shortness of breath.