COVID Vaccination Rates in Children and Adults with Sickle Cell Disease in British Columbia, Canada
Authors: Merkeley Hayley , McGuire Marlee , Ding Lillian , McCartney Heather , Amid Ali , Strahlendorf Caron , Sandhu Nina , Vergidis Dimitrios , O'Donnell Maureen 
Published: November 2021

Abstract
Background: Persons with Sickle Cell Disease (SCD) infected with the SARS CoV-2 virus have significantly increased risks of hospitalization and death and are strongly recommended to be fully vaccinated. Vaccine hesitancy has previously been described in the SCD population and uptake of other recommended vaccines has been reported to be low in some studies. The goal of this study was to assess how vaccination rates amongst eligible pediatric and adult SCD patients in British Columbia (BC), Canada, compared to those of the general population and other "clinically extremely vulnerable" (CEV) groups.
Methods: Persons age 12 and over with SCD in BC were identified as a CEV population and prioritized for immunization. A comprehensive process was undertaken to find and identify all CEV patients in BC and notify them of their priority status. Individuals diagnosed with SCD in the province were identified in the shared pediatric and adult patient registry (iCHIP), which tracks demographics, diagnoses and therapies, and added to the CEV patient list. SCD patients were notified of their priority status through standard mail from the provincial health officer, as well as emails and phone calls from the pediatric and adult SCD programs. Those aged 16+ were invited to register for immunization beginning in March 2021 while those 12-15 years were permitted to register starting in May 2021. Adult patients were eligible to receive mRNA vaccines from Pfizer and Moderna as well as the Astra-Zeneca (AZ) COVISHIELD vaccine, while those aged 12-17 were eligible only for Pfizer vaccines. The provincial immunization registry (PIR) was interrogated to confirm vaccine administration. The main outcome measure was the proportion of SCD patients who received 1st and 2nd dose COVID vaccines.
Results: 138 individuals age 12+ with SCD were identified in the iCHIP database. 71.0% had Sickle Cell Anemia (SCA), 25.4% had Hemoglobin SC (Hb SC) and 3.6% had other genotypes. Participants ranged in age from 12-69 years with a median of 28 years. 67.4% were receiving disease-modifying therapy (76 were on hydroxyurea, 11 on regular red cell exchange, 1 was receiving crizanlizumab, and 5 with Hb SC were phlebotomized). None were treated with gene therapy or transplant. 7 individuals had a PCR-confirmed SARS CoV-2 infection prior, but none following immunization.
As of July 30, 2021: 68.8% of persons with SCD received a 1st and 55.1% received a 2nd dose of COVID vaccine. Almost all doses were mRNA-based vaccines with the exception of a single 1st dose administration of AZ. Vaccination rates amongst different age ranges and genotypes are displayed in Table 1. Patients with SCA did not have significantly different vaccination rates compared to those with Hb SC/other genotypes: 64.3% versus 80.0% for 1st dose (p=0.0703) and 48.0% versus 62.5% (p =0.12114) for 2nd dose.
Vaccination rates amongst the SCD group were compared to other age matched CEV populations as well as the general provincial population and are detailed in Tables 2 and 3. A higher proportion of persons with SCD under the age of 20 received 1st dose (70.8% versus 31.1%; p&lt;0.00001) and 2nd dose (50.0 versus 15.3%; p &lt;0.00001) of vaccines compared to the general population. However, a lower proportion age 20-49 and 50+ years old received a 1st dose as demonstrated in Table 2. In addition, lower proportions of persons with SCD of all age ranges were vaccinated in comparison to other CEV groups. As demonstrated in Table 3, SCD was not associated with receiving a 1st dose vaccine compared to the general BC population (OR 0.8, 0.56 to 1.16 95% CI, p=0.2481). In contrast, persons in other CEV groups were twice as likely to receive a first dose COVID immunization compared to the general BC population (p&lt;0.0001).
No severe vaccine-related complications including vaccine-induced immune thrombotic thrombocytopenia (VITT) were reported. There were 7 presentations to hospital for vaso-occlusive crises (VOC) within 21 days of immunization.
Conclusion: Despite an active CEV process to find and invite persons with SCD to be vaccinated, these data demonstrate that vaccination rates amongst persons with SCD in BC are below those of other CEV age-matched groups. Vaccination rates amongst adults are also lower than the general population, however there is a high vaccination rate in persons under 20 years old. A subsequent qualitative study exploring COVID vaccine hesitancy amongst persons with SCD in BC is being explored.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.