Background and Aims SARS-CoV-2 represents a challenge for hemodialysis (HD) patients due to their multiple comorbidities, disturbed immune defenses in the setting of kidney disease and increased age. Furthermore, sharing collective spaces during HD sessions increases the risk of contamination. In March 2020, the first COVID-19 cases in Portugal occurred in Felgueiras, a municipality belonging to the district of Porto. The HD unit that serves this population has 69 in-center patients and, from March 2020 until January 2021, has had 14 COVID-19 cases. We describe our experience concerning patient management and their clinical characteristics. Method Clinical and laboratory data were collected. We aimed at assessing the impact of the infection in hemoglobin, alanine transaminase, several electrolytes - potassium, phosphorus, sodium and calcium - as well as the normalized protein catabolic rate (nPCR) comparing results from the month before infection with those of the month after cure. Statistical analysis used SPSS® and variables were compared using paired-samples t-test. Results We used a dedicated room and staff for COVID-19 patients, disinfection protocols and specific routes. Transportation was done with a maximum of 3 patients in a 9-seater vehicle, all patients used masks, practiced social distancing, were asked for symptoms and had their temperature measured on each HD session. SARS-CoV-2 infection was established by reverse transcription polymerase chain reaction on nasal and oropharyngeal swabs. Of the 14 cases, 3 occurred in March, 5 from October until Christmas and 6 from then onwards, accounting for approximately 20% of the unit’s patients. Of these, 2 were asymptomatic, 6 had predominantly respiratory symptoms, 1 had fever and 1 had gastrointestinal symptoms. Three were hospitalized, 2 died due to COVID-19 and 1 died 1 month after cure due to advanced cancer. Mean age of these patients was 70±13.2; 5 were females and 6 had diabetic nephropathy. Only 7 patients had post-COVID-19 results for comparison. The mean hemoglobin value before COVID-19 was 10.5±1.7g/dL and did not change significantly after COVID-19. Although phosphorous dropped from a mean 3.8±0.9mg/dL to 3.2±1.3mg/dL, this difference did not reach significance (p=0.43). All other electrolytes remained stable. nPCR dropped from 1.23±0.47 to 0.95±0.37 although not a significant difference (p=0.24). Five patients were tested for IgG/IgM antibodies against SARS-CoV-2 one month after cure using Elecsys® qualitative immunoassay and 4 tested positive. Conclusion COVID-19 is a problem for HD patients where the percent of cases is larger than in the general population. Our 3 first cases and the 4 last cases shared the same HD shift and occurred in the same period confirming that, despite all protective measures, sharing the facilities in close proximity is a risk factor. Respiratory symptoms predominated but were only severe requiring hospital admission in 3 patients. Mortality represented 14% and the 2 patients whose death was attributable to COVID-19 had an increased burden of comorbidities and were old. Seroconversion was high 1 month after the disease. The only patient who tested negative for antibodies had been asymptomatic raising doubts about whether there could have been false test results or an undetectable immune response.

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 < 0.001). This difference remained significant even if those who had COVID-19 were removed from the analysis (p < 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 < 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 < 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.