Hematologic adverse events following COVID-19 vaccination and revaccination in persons aged 12 and above: A Canadian Immunization Research Network study

Data on safety of revaccination after a hematologic adverse event following immunization (AEFI) with COVID-19 vaccines are limited. This study characterized hematologic AEFIs in patients assessed by Canadian Special Immunization Clinic (SIC) network physicians from January 2021 to February 2023 and estimated recurrence rates of hematologic events after revaccination. Following clinical assessment of 475 individuals, revaccinated participants were followed for recurrence of AEFI. Thirty-eight cases (21 55.3% males and 17 44.7% females) with hematologic AEFIs and aged ≥12 were included in the analysis; 31/38 participants (81.6%) were 18 to 64 y old. Immune thrombocytopenia, deep vein thrombosis and pulmonary embolism were the most common diagnoses, accounting for 11 (28.9%), 9 (23.7%) and 9 (23.7%), cases. Two cases of thrombosis with thrombocytopenia syndrome (TTS) were reported after ChAdOx1. The vaccines associated with hematologic AEFIs were BNT162b2 (17, 44.7%), ChAdOx1 (11, 28.9%), and mRNA-1273 (10, 26.3%). Twenty-seven (71.1%) participants were revaccinated; 14 (51.9%) received the same vaccine product as their initial vaccine while 13 (48.1%) received a different product. There were no recurrences of the same AEFI reported after revaccination with an mRNA vaccine, including the two patients with TTS, suggesting that hematologic AEFI recurrences following COVID-19 vaccines are likely uncommon.