Pb2514: immunogenicity of anti-sars-cov-2 vaccines in patients with severe sickle cell disease

Topic: 26. Sickle cell disease Background: Several studies of small numbers of patients with sickle cell disease (SCD) have evidenced the efficacy of new m-RNA technology anti-SARS-CoV-2 vaccines in this population. Little information is available on regularly transfused patients with severe SCD. Aims: In a study conducted at a French SCD reference center, we sought to confirm the immunogenicity of anti-SARS-CoV-2 vaccines in patients with severe transfused SCD patients. Methods: We retrospectively assessed anti-SARS-CoV-2 (anti-spike IgG) serologic data collected during routine clinical care between January 1st and December 31st, 2021, among the adult SCD patients (aged 18 and over) transfused in our biotherapy department and who had received at least one injection of anti-SARS-CoV-2 vaccine during the same period. The data included the date of the serology assay, the anti-spike IgG titer, the vaccination date, the type of vaccine, age, sex, hydroxyurea (HU) treatment and the transfusion program. The antibody titers were measured using the SARS-CoV-2 IgG II Quant. Alinity, Abbott kit before and after each injection and expressed in binding antibody units (BAU)/ml. Serology was positive at a cut-off level of 20 BAU/mL. Patients who did not have at least one pre-vaccination serology and one post-vaccination serology (after the first or second dose) were excluded. Post-vaccination serologies were collected at least 21 days after last injection to ensure seroconversion. Results: We included 75 patients between January 1st and December 31st 2021, and 46 were excluded (flow chart). Characteristics of 29 remaining patient are summarized in Table 1. All of them had the SS genotype. The Pfizer-BioNTech vaccine was used for 15/18 (83%) of the first doses and 11/13 (85%) of the second doses. Prior to the first injection, 29 patients had at least one serology assay. The median antibody level was 40 BAU/ml [0–594]. The median time interval between the pre-vaccination serology assay to the first vaccine injection was 33 days [0-105]. Between the first and second injections, 18 patients had at least one serology assay. All of them were seropositive: the median titer was 1766 BAU/ml [107–5634]. The median time interval between the first injection and the serology assay was 48 days [23-136]. After the second injection, 13 patients had at least one serology assay. The median antibody level was 1329 BAU/ml [246–5634]. The median time interval between the second injection and the following serology assay was 81 days [25–205]. Summary/Conclusion: Our results show that immune response (antibody production) to anti-SARS-CoV-2 vaccines is good in a severe SCD cohort, as reported by Haggenburg et al. with a seropositivity rate of 96% in 31 SCD adult patients on HU. Green et al. reported full (100%) seroconversion after COVID-19 or after at least one vaccine injection in 36 SCD adult and pediatric patients, as also observed in a control population. The present study had some limitations, including the absence of a control population and the retrospective design; these aspects might account for disparities in the time intervals between injections and serology assays. We could not compare the vaccine response according to the history of clinical COVID-19, because of passive antibodies brought by transfusions which could positive the pre-vaccination serology. We conclude that anti-SARS-CoV-2 mRNA vaccines (particularly the Pfizer-BioNTech vaccine) are effective in patients with severe SCD. These reassuring data should help to convince patients who are reluctant. Table 1. CharacteristicsKeywords: Sickle cell disease, Vaccination, COVID-19