Second-dose ChAdOx1 and BNT162b2 COVID-19 vaccines and thrombocytopenic, thromboembolic and hemorrhagic events in Scotland

Simpson, Colin R. and Kerr, Steven and Katikireddi, Srinivasa Vittal and McCowan, Colin and Ritchie, Lewis D. and Pan, Jiafeng and Stock, Sarah J and Rudan, Igor and Tsang, Ruby S. M. and de Lusignan, Simon and Hobbs, F. D. Richard and Akbari, Ashley and Lyons, Ronan A. and Robertson, Chris and Sheikh, Aziz (2022) Second-dose ChAdOx1 and BNT162b2 COVID-19 vaccines and thrombocytopenic, thromboembolic and hemorrhagic events in Scotland. Nature Communications, 13 (1). 4800. ISSN 2041-1723 (

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We investigated thrombocytopenic, thromboembolic and hemorrhagic events following a second dose of ChAdOx1 and BNT162b2 using a self-controlled case series analysis. We used a national prospective cohort with 2.0 million(m) adults vaccinated with two doses of ChAdOx or 1.6 m with BNT162b2. The incidence rate ratio (IRR) for idiopathic thrombocytopenic purpura (ITP) 14-20 days post-ChAdOx1 second dose was 2.14, 95% confidence interval (CI) 0.90-5.08. The incidence of ITP post-second dose ChAdOx1 was 0.59 (0.37-0.89) per 100,000 doses. No evidence of an increased risk of CVST was found for the 0-27 day risk period (IRR 0.83, 95% CI 0.16 to 4.26). However, few (≤5) events arose within this risk period. It is perhaps noteworthy that these events all clustered in the 7-13 day period (IRR 4.06, 95% CI 0.94 to 17.51). No other associations were found for second dose ChAdOx1, or any association for second dose BNT162b2 vaccination. Second dose ChAdOx1 vaccination was associated with increased borderline risks of ITP and CVST events. However, these events were rare thus providing reassurance about the safety of these vaccines. Further analyses including more cases are required to determine more precisely the risk profile for ITP and CVST after a second dose of ChAdOx1 vaccine.


Simpson, Colin R., Kerr, Steven, Katikireddi, Srinivasa Vittal, McCowan, Colin, Ritchie, Lewis D., Pan, Jiafeng ORCID logoORCID:, Stock, Sarah J, Rudan, Igor, Tsang, Ruby S. M., de Lusignan, Simon, Hobbs, F. D. Richard, Akbari, Ashley, Lyons, Ronan A., Robertson, Chris and Sheikh, Aziz;