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

Thirty-eight cases with hematologic AEFIs following COVID-19 vaccination were identified among 475 individuals assessed by Canadian Special Immunization Clinic network physicians.

• The study period spanned January 2021 to February 2023.
• 21 (55.3%) of the 38 cases were male and 17 (44.7%) were female.
• 31/38 participants (81.6%) were 18 to 64 years old.
• Participants were aged 12 and above.

Immune thrombocytopenia, deep vein thrombosis, and pulmonary embolism were the most common hematologic AEFI diagnoses.

• Immune thrombocytopenia accounted for 11 cases (28.9%).
• Deep vein thrombosis accounted for 9 cases (23.7%).
• Pulmonary embolism accounted for 9 cases (23.7%).
• Two cases of thrombosis with thrombocytopenia syndrome (TTS) were reported, both after ChAdOx1.

BNT162b2 was the vaccine most commonly associated with hematologic AEFIs, followed by ChAdOx1 and mRNA-1273.

• BNT162b2 was associated with 17 cases (44.7%).
• ChAdOx1 was associated with 11 cases (28.9%).
• mRNA-1273 was associated with 10 cases (26.3%).

The majority of participants with hematologic AEFIs were subsequently revaccinated.

• 27 out of 38 (71.1%) participants were revaccinated.
• 14 (51.9%) of revaccinated participants received the same vaccine product as their initial vaccine.
• 13 (48.1%) of revaccinated participants received a different vaccine product.

No recurrences of the same hematologic AEFI were reported after revaccination with an mRNA vaccine.

• This included the two patients who had experienced thrombosis with thrombocytopenia syndrome (TTS) after ChAdOx1.
• The absence of recurrences was observed across all hematologic AEFI types in the revaccinated cohort.
• The authors concluded that hematologic AEFI recurrences following COVID-19 vaccines are 'likely uncommon.'