MO1058: Antibody Response to COVID-19 Vaccination Among Hemodialysis Patients: A Case-Control Study
Authors: Homem Melo Marques Sofia , Do Sameiro Faria Maria , Balboa Martin , Beco Ana , Vales Cecília , Pombal Rita , Cruz Gomes Helena 
Published: May 2022

Abstract

BACKGROUND AND AIMS
SARS-CoV-2 represents a challenge for hemodialysis (HD) patients due to their diminished immune defenses in the setting of kidney disease, multiple comorbidities and older age. COVID-19 vaccines have brought hope but these patients’ reduced response to immunization with the hepatitis B and influenza vaccination raised concerns about a lower efficacy of the new vaccines. This study aimed at quantifying IgG in sequential samples from HD patients and compare its titers with those of a non-HD healthy population, after vaccination.

METHOD
We compared IgG titers using Abbott SARS-CoV-2 IgG II Quantitative Antibody Assay on the Alinity i system (Abbott Diagnostics, Chicago, US), 3–4 months after the Pfizer-BioNTech COVID-19 vaccine in 54 HD patients and 59 non-HD controls. This method is a two-step chemiluminescent microparticle immunoassay used for the quantitative determination of IgG antibodies to the receptor binding domain of the S1 subunit of the spike protein of SARS-CoV-2. HD patients performed their treatments at the HD unit of Felgueiras, a municipality in the district of Porto, Portugal, and were vaccinated in January/February 2021. The controls were healthcare workers from the hospital of Gaia. All HD patients received 2 vaccine doses even if they had previously had COVID-19 (N = 8) whereas controls only received 1 dose of the vaccine if they had been infected (N = 28). For 48 of the HD patients, we reassessed IgG levels 8 months after vaccination and compared it with the first measurements. Statistical analysis used SPSS®. Parametric variables were described with mean ± standard deviation and compared using independent and paired-samples t-tests. Non parametric variables were described with median ± interquartile range (IQR) and compared using Mann-Whitney U and Wilcoxon tests.

RESULTS
HD patients were older (67.6 ± 15.8 years of age) when compared to the healthy controls (42.4 ± 12.1 years of age). Only 1 HD patient had IgG below the positive cutoff after vaccination, all others seroconverted. Median values were significantly lower among HD patients compared to the controls (973 IQR 387–3306 versus 4809 IQR 2557–7746 AU/mL; p &lt; 0.001). This difference remained significant even if those who had COVID-19 were removed from the analysis (p &lt; 0.001). Those who had had COVID-19 before vaccination, showed significantly increased IgG levels compared to those who had not (6956 IQR 4810–13 101 versus 1520 IQR 554–3950 AU/mL; p &lt; 0.001), a similar finding among HD and non-HD individuals. In HD patients for whom this data was available, IgG levels decayed from month 4 to month 8 (973 IQR 387–3306 versus 382 IQR 168–2071 AU/mL; p &lt; 0.001).

CONCLUSION
HD patients seem to have an impaired immune response after the COVID-19 vaccines, similar to what happens with vaccines against other viruses. After the Pfizer-BioNTech COVID-19 vaccine 98% of the patients seroconverted. Although they were older which may have played a role, a limitation to the analysis, IgG titers were lower in HD-patients than in the control group. Antibodies declined over the next months. This decline may be associated with loss of neutralizing antibodies, cellular responses to SARS-CoV-2 and risk of reinfection.