Persistence of antibody response to SARS-CoV-2 in a cohort of haemodialysis patients with COVID-19

Background. Haemodialysis (HD) patients are extremely vulnerable to coronavirus disease 2019 (COVID-19). Their immune response after infection is unclear. We have found high seroconversion rates in this population, with 95% developing antibodies. It is unclear if and how long these antibodies persist. Here we investigate this with serial antibody (Ab) testing. Methods. We identified HD patients who had confirmedsevere acute respiratory syndrome coronavirus 2 between March and May 2020 and measured monthly antibodies (immunoglobulin G/immunoglobulin M) in those who survived. We used a semiquantitative cut-off index to create a qualitative result and plotted optical density (OD) over time. We used linear regression to examine the slope, as well as noting peak OD and time to peak OD. We correlated these against baseline demographics, markers of illness severity and comorbidities. Results. A total of 122 patients were analysed. All remained Ab positive during follow-up for a minimum of 148 days. Seventyone percent had a positive gradient indicating increasing Ab positivity over time. We found that age (P = 0.01), duration of polymerase chain reaction positivity (P = 0.06) and the presence of symptoms (P = 0.05) were associated with a longer time to peak OD. Immunosuppression did not alter peak OD but did lead to a non-significant increase in time to peak OD, and more patients had a subsequent decrease in Ab levels (P = 0.02). Diabetic patients were more likely to have a positive slope (odds ratio 2.26). Conclusions. These results indicate that HD patients have a robust and sustained Ab response after confirmed COVID-19 infection with no suggestion that immunosuppression weakens this response. Although it is unclear what protection these antibodies confer, this is encouraging that HD patients should respond to vaccination.