Adverse Events Following COVID-19 Vaccination in Transfusion-Dependent -Thalassemia Patients

Introduction: Patients with transfusion-dependent-thalassemia (TDT) are considered as increased risk population for severe and/or morbid COVID-19 infection. Timely vaccination is the main preventive method for severe COVID-19. Different adverse events and reactions following vaccination have been reported, with severe ones being extremely rare. TDT patients may have altered immunity due to chronic transfusions, iron overload and chelation therapy, and splenic dysfunction. The safety profile of vaccination in chronically transfused patients with thalassemia has not been reported.

AIM: To evaluate the safety profile of COVID-19 vaccines in TDT patients.

Patients and Methods: This is a single institution's, retrospective analysis evaluating all TDT patients, older than 18 years old, who had completed the vaccination protocol at least 30 days before data cut-off time (July 20 ^th 2021). Adverse events were reported by patients up to 30 days post each dose. Demographic data and hematological data, including mean hemoglobin levels before and up to 30 days after each dose, were recorded. T-test was performed to investigate changes in hematological profile and transfusion burden post vaccination.

Results:186 patients (median age:45; range:18-61 years old; male/female:87/99) were included for data analysis corresponding to 53% of all TDT patients followed in our Thalassemia Unit. Distribution of vaccine types were: Comirnaty -BNT162b2 (Pfizer Inc. and BioNTech)90.86% (n =168), Vaxzevria (previously COVID-19 vaccine, AstraZeneca)1.61% (n=3), Moderna (Moderna TX Inc.)6.99% (n =13) and JNJ-78436735 (Janssen Pharmaceuticals Companies of Johnson & Johnson)0.54% (n =2). No patients had confirmed or suspected previous COVID-19 infection.

Adverse events were graded according to Common Terminology Criteria for Adverse Events (CTCAE) v5.0. The incidence of adverse events after 1 ^st and 2 ^nd dose were 43.5% (81/186) and 54.8% (102/186), respectively. Adverse events after 1 ^st dose included pain at injection site 26.3%( n=49), fatigue 9.7%(n=18), fever 5.4% (n=10),headaches 4.3% (n=8), arthralgia and myalgia 2.2% (n=4), and lymphadenopathy 0.5% (n=1). Adverse events after 2 ^nd dose included fever 28.5% (n=53), fatigue 17.7% (n=33), pain at injection site 15.6%(n=29), arthralgia and myalgia 11.3% (n=21), headaches 9.1% (n=17), lymphadenopathy 3.2% (n=6), dizziness 0,5% (n=1), tachycardia 0.5% (n=1), diarrhea/ vomiting 0.05% (n=1) and amaurosis fugax 0.5%: (n=1). No grade 4-5 events or anaphylaxis were observed. Two patients (both males, 51 years and 45 years old, respectively) presented with acute hemolytic crisis with hemoglobinuria in 3 ^rd and 20 ^th day after the second dose with Pfizer/BioNTech, respectively. They are receiving treatment with corticosteroids without partial response. Both patients had a history of acute hemolysis crisis within the last 3 years. A decrease in Hb levels after either the first or second dose compared to pre-vaccination mean Hb levels was observed (mean=9.9 /sd=0.63 vs mean=9.44 /sd=0.76), (p < 0.001).

Conclusions: Compared to the vaccine trials, we observed some lower incidence of vaccine-related adverse events in our cohort of TDT patients, which may be related to the less stringent reporting methods outside official trials. A temporary drop in hemoglobin levels may be noted in chronically transfusion patients, which parallels what is observed when patients are developing infection or inflammation. Of interest, two patients with previous history of alloimmunization, developed hemolysis. Close hematological follow up may be required in TDT patients post vaccination. The risk/benefit of the vaccination is strongly positive for this vulnerable population.