Most dialysis patients who have been infected with SARS-CoV-2 maintain protective antibody levels over 6 months' follow-up, including subgroups at risk of impaired immunity, reports a study in Annals of Internal Medicine (1).
The study investigators used remainder plasma samples from 2215 hemodialysis patients from 1200 dialysis facilities across the United States. Fifty-three percent of patients lived in majority-minority neighborhoods and 44% in low-income neighborhoods (at least 20% below the federal poverty level).
All samples included in the study were positive for SARS-CoV-2 receptor-binding domain (RBD) total antibodies, tested using the highly sensitive and specific Siemens semiquantitative assay in July 2020. Follow-up samples from routine monthly laboratory tests were used to monitor RBD immunoglobulin G (IgG) index values over 6 months. Persistence of RBD antibodies was assessed, including analysis by antibody response level, age, race/ethnicity, and diabetes status.
Ninety-three percent of patients had a detectable response, defined as an IgG index value of 1 or greater. In July 2020, 60% of patients had high IgG index values (10 or greater). About three-fourths of patients in this group continued to have high index levels throughout follow-up.
Follow-up samples for these individuals showed a “small and continuous decline” in RBD IgG levels. Adjusted median values fell from 21 in July 2020 to 13 in December 2020. This pattern was consistent in subgroups defined by age, sex, race/ethnicity, and diabetes status. Patients with consistently undetectable antibody responses were more likely to be White, to be in the younger (18 to 44 years) or older (over 80 years) age groups, and to have diabetes and hypoalbuminemia.
“Our study is the largest to describe longitudinal humoral response in a population that reflects groups most affected by SARS-CoV-2 infection,” the researchers write. They note some important limitations, including the lack of data on symptoms or reverse transcription-polymerase chain reaction testing. The study was also limited to patients who survived COVID-19.
The findings suggest that nearly all seroprevalent dialysis patients have a detectable RBD IgG response through at least 6 months' follow-up. There is no indication of shorter-lived antibody responses among subgroups at highest risk of impaired immunity, such as older adults or those with diabetes. The investigators conclude, “Our study…provides a benchmark for clinicians and researchers assessing humoral response after infection or vaccination in susceptible populations.”
Anand S, et al. Serial SARS-CoV-2 receptor-binding domain antibody responses in patients receiving dialysis. Ann Intern Med [published online ahead of print May 18, 2021]. doi: 10.7326/M21-0256; https://www.acpjournals.org/doi/10.7326/M21-0256