Does Covishield (ChAdOx1 nCoV-19) cause thrombosis (blood clots)?

Covishield (ChAdOx1 nCoV-19) and Blood Clots

Yes, Covishield (ChAdOx1 nCoV-19) can cause rare but potentially serious blood clots, specifically a condition called Vaccine-Induced Immune Thrombocytopenia and Thrombosis (VITT) or Thrombosis with Thrombocytopenia Syndrome (TTS). 1, 2, 3

Evidence for Blood Clots with Covishield

• Covishield (ChAdOx1 nCoV-19), marketed as AstraZeneca-Oxford COVID-19 vaccine in many countries, has been associated with a rare but serious adverse effect called Vaccine-Induced Immune Thrombocytopenia and Thrombosis (VITT) 1
• The manufacturer (AstraZeneca) has legally admitted in a UK court that their COVID-19 vaccine could cause this rare and potentially fatal blood clotting disorder 2
• Case reports have documented TTS occurring approximately 5-30 days after vaccination with ChAdOx1 nCoV-19 1, 3
• The condition involves anti-platelet factor 4 (PF4) antibodies that arise following vaccination and lead to intense activation of platelets and the coagulation system 1

Clinical Characteristics of VITT/TTS

• Symptoms typically begin 5 to 30 days after vaccination and include severe or unusual headaches, new unexplained pinprick bruising or bleeding, shortness of breath, leg swelling, or persistent abdominal pain 1
• Thrombosis affects the cerebral veins in 50% of cases, but any arterial or venous vascular bed may be involved, and around one-third of patients have thrombosis in multiple sites 1
• The condition involves both thrombosis (blood clots) and thrombocytopenia (low platelet count) occurring simultaneously 1, 3
• Case reports have documented both venous and arterial thrombosis patterns, including cerebral venous sinus thrombosis, portal vein thrombosis, and arterial thrombosis 3, 4

Incidence and Risk Factors

• VITT is rare, with an incidence of 14.9 per million after first or unknown dose of COVID-19 vaccine, and 1.8 cases per million after second doses 1
• The incidence rate in adults aged 18-49 years is twice that of adults 50 years and older 1
• This risk profile differs from mRNA vaccines (Pfizer-BioNTech and Moderna), which have not shown disproportional reporting of thromboembolic events in younger women 5

Management of VITT/TTS

• Management includes anticoagulation with non-heparin based anticoagulants, which should be started as soon as possible, and intravenous immunoglobulin 1
• Early diagnosis and prompt intervention are critical for patient management 3
• D-dimer testing can help identify patients at risk, with levels >5 mg/mL associated with a high thrombotic risk (positive predictive value of at least 40-50%) 1

Risk-Benefit Considerations

• Despite the risk of VITT, risk-benefit analyses suggest that during periods of high COVID-19 infection rates, vaccination may still decrease the overall risk of blood clots 6
• This is because COVID-19 infection itself is associated with a higher risk of thrombotic complications than vaccination 6
• COVID-19 infection has been associated with coagulopathy due to inflammatory response, endothelial dysfunction, and a pro-thrombotic state 1

Clinical Implications

• Healthcare providers should be vigilant for symptoms of VITT occurring 5-30 days post-vaccination with ChAdOx1 nCoV-19 1
• Patients should be informed about warning signs that require immediate medical attention (severe headache, visual changes, multiple small bruises, shortness of breath, chest pain, leg swelling, persistent abdominal pain) 1
• Alternative vaccine options (such as mRNA vaccines) might be considered for younger adults, particularly women, who have a higher relative risk of this complication 1, 5

While VITT/TTS is a serious adverse effect, it is important to note that it is rare, and the overall benefit-risk assessment of COVID-19 vaccination must consider the substantial risks associated with COVID-19 infection itself, which also carries significant thrombotic risks.