The SARS-CoV-2 pandemic has proved to be a real challenge for hospitals and hemodialysis units, in most cases resulting in the collapse of the healthcare system. SARS-CoV-2 infection ranges from asymptomatic or mild respiratory illness to severe pneumonia with respiratory distress syndrome, septic shock and multiorgan failure. Patients receiving chronic hemodialysis (HD) treatment are more susceptible to SARS-CoV-2 infection with increased risk of complications and mortality.1,2 Special attention should be paid to risk factors for infection,3 and vaccination should be prioritized in these patients.4 It is well known that dialysis patients may have a reduced response to vaccination,5 so our objective was to evaluate this premise in our patients, as well as to analyse whether there are factors related to the development of humoral response in HD patients and describe the situation in our unit. This is a descriptive study in which data were collected from 74 patients in a chronic HD program. All, with the exception of one patient who did not receive any dose by choice, had been vaccinated. Three types of vaccine were administered: Pfizer-BioNTech, Astrazeneca and Moderna. Participants received the complete vaccination schedule (two doses plus a booster) at least three months prior to the study, 12 patients had also received a fourth dose at least one week prior to the start of the study.
Data were collected from medical and laboratory records, using the following variables: age, sex, diabetes, hepatitis B, transplant candidacy, type of dialysis access, dialysis dose by kt/V, type of vaccine and number of doses, albuminemia, leukocytes, lymphocytes, past infection, and serology.
Data are presented as mean for continuous variables and as number of patients and percentage in each group for categorical variables. For the analysis of the variables sex, hepatitis, diabetes, transplant candidacy, dialysis access, dialysis dose, type of vaccine, albuminemia, chi-square with Fisher's exact test was used to compare them with positive results for humoral response. The age variable was analysed using the T test for means equality. Pearson's chi-square test was used to compare the variables of number of vaccinations. P=0.05 was considered statistically significant for all analyses. IBM SPSS Statistics, version 22, was used for all statistical analyses.
All but one of the included patients were Caucasian. The prevalence of SARS-CoV-2 infection was 35%.
97% of patients had a positive serology against SARS-CoV-2, only 3% did not achieve immunity, even though they had received a complete vaccination regimen. Of the 38 patients who received the Pzifer-BioNTech vaccine, 37 developed positive serology. Thirty-three patients received the Moderna vaccine where 100% developed positive serology, as did the 2 patients vaccinated with Astrazeneca.
Regarding HD dose, 61 patients had a Kt/v>=1.4. We used albumin to measure the degree of nutrition, 19 patients were found with albumin <3,5g/dl, however 18 of these had a positive serology. No statistically significant relationship was found between having positive serology and the variables of age, sex, diabetes, hepatitis B, transplant candidacy, dialysis dose, type of vaccine, albuminemia, leukocytes or lymphocytes. Of the total of 74 patients, 34 dialyzed by indwelling catheter and 40 with AVF, no significance was found between access to HD and development of serology against SARS-CoV-2 (p>0.208). A statistically significant association was obtained between the number of doses received and the development of humoral response with p=0.0001.
Our main finding is that the majority of patients on chronic HD developed a substantial humoral response after the two vaccine doses.
The cut-off for a positive response in our study was 33.8 BAU/mL, and >80% of our cohort was well above this threshold with levels >2080. Notably, one of the subjects who did not develop a response was on rituximab treatment.
Our study has several limitations, the most important of which is the sample size. In many countries, the incidence and/or severity of COVID-19 have differed according to ethnicity, which we were unable to investigate due to the homogeneous nature of our population. In addition, 26 patients have had COVID-19 infection at some point so we cannot explain whether their antibody level is due to vaccination or infection, in addition to possible asymptomatic infections that may have been present.
In conclusion, patients on chronic HD developed a substantial humoral immune response after the full dose of vaccination. This finding is reassuring and should encourage HD patients and their caregivers to receive the vaccine. However, further research remains to be done in order to understand the mechanism of action and humoral defence against SARS-CoV-2 and to promote the idea of reinforcing the dose or vaccination program in hemodialysis patients.
