Low sars-cov-2 seroprevalence in a cohort of sickle cell disease (scd) patients: Possible effects of emphasis on social isolation for a population initially considered to be at very high risk

ABSTRACT

Background: Although initially considered at higher risk for severe presentations of COVID-19, observational studies with SCD patients have mostly pointed to clinical severity similar to the general population. However, the level of vulnerability of these individuals to become infected and the determinants for their contagion are still uncertain. Aims: To assess the prevalence of SARS-Cov-2 antibodies in SCD patients followed at a Brazilian center and its correlation with phenotypic and socioeconomic determinants. Methods: A questionnaire was applied regarding demographics, socioeconomic status, use of Hydroxyurea, working status and income, COVID-19 symptoms, and the perceptions about social isolation measures. Blood samples were taken for chemoluminescence IgG (anti-N) and IgM (anti-S) anti-SARS-CoV-2 tests (Abbott Architect™, Ireland);specific neutralizing antibody titers were accessed observing the cytopathic effect in cells incubated with patient serum-virus mixture. Results: From Jul/20 to Jan/21, 214 serological tests were performed on135 patients (86% of SCD patients registered at the center) 82 HbSS (61%), 41HbSC (30%), 8Sβ+ (6%), 4Sβ0 (3%);57% male and median age 42 (19-74). 66% were using Hydroxyurea and 4% were on chronic transfusion. In the analyzed period, 61 (45%) patients had vasoocclusive crises;37 (27%) had symptoms suggestive of COVID-19, but only 2 patients had a positive PCR for SARS-Cov-2. When questioned, only12% of patients did not consider themselves vulnerable to infection, and only17% believed that individual and collective protection measures were expendable. In fact, 91% stated that they were able to adopt basic social distance measures, with 76% reporting cancellation of social events and 64% managed to reduce the use of public transport, but only 44% could work or study remotely. Regarding serological evaluation, 57 patients (42%) were tested more than1 time during this period 46 with 2 tests,11 with ≥ 3 tests. Among all patients,15 had positive results: 9 IgG/IgM+ and 6 IgG+ only, therefore with an overall seroprevalence of11%. Seroconversion was documented for only1 patient during the study period and, interestingly, with no signs and symptoms of infection. Moreover, 2 patients lost positivity for IgG 3 months after the initial positive test. The search for functionally neutralizing antibodies resulted in 9 patients with low titers (□140) and only 3 patients with remarkably high titers (≥1640). There were no correlations between test positivity and education, income, number of household contacts and maintenance of work outside the home;however, serological positivity was associated with older age (40.3 x 22.9, p<.001) and regular use of public transport (Fisher exact test, p=0.02). Only1 patient in this cohort needed hospitalization for COVID-19, including mechanical ventilation and exchange transfusions, but was discharged after14 days Summary/Conclusion: These data attest to the effectiveness of social distancing instructions given to patients in our SCD clinic throughout the pandemic, considering the low overall positivity and only1 seroconversion during the study period. The fact that only1 patient in our center had severe disease agrees with other reports showing less severity for SCD than initially expected. In fact, the transient positivity of serological tests and the low levels of functional neutralizing antibodies in SCD patients may indicate the acquisition of protective immune responses that are not dependent on antibodies and that still need to be better evaluated.