Patients receiving maintenance hemodialysis face substantial risk of morbidity and mortality associated with COVID-19 infection. Early studies have shown that two doses of a SARS-CoV-2 messenger RNA vaccine elicit a seroresponse in more than 90% of patients on maintenance hemodialysis, but that response is lower compared with the general population.
In late June 2021 when the Delta variant became the dominant SARS-CoV-2 strain in the United States, the rate of breakthrough infection among those fully vaccinated was higher than expected. Among initial responders to the vaccine, more than half had waning immunity by 4 to 6 months. Waning immunity was particularly noted in those whose initial response was lesser.
There are few data on the impact of lesser initial vaccine response and subsequent waning antibody levels on clinical outcomes among patients on maintenance dialysis. Harold J. Manley, PharmD, and colleagues conducted a retrospective, observational study to describe the incidence of COVID-19 diagnoses and COVID-19-related hospitalization or death in unvaccinated, partially vaccinated, and fully vaccinated adults on dialysis during the pre-Delta and Delta-dominant periods. The researchers also sought to examine the association between antibody levels and clinical outcomes in those patient populations. Results were reported in the American Journal of Kidney Diseases.
Eligible study participants were adults 18 years of age or older with no history of COVID-19 receiving hemodialysis through a national provider and treated between February 1 and December 18, 2021.
The outcomes of interest were all SARS-CoV-2 infections and a composite of hospitalization or death following COVID-19. COVID-19 case rates and vaccine effectiveness were determined using logistic regression analysis. All new COVID-19 diagnoses that occurred during the study period were assigned to the appropriate vaccination status at the time of diagnosis: unvaccinated, partially vaccinated, or fully vaccinated.
COVID-19 cases, hospitalizations, and deaths were identified during the study period and further divided into pre-COVID-19 Delta variant (February 1 to June 25, 2021) and COVID-19 Delta variant-dominant (June 26 to December 18, 2021) periods. Those diagnosed with COVID-19 were followed for hospitalization or death through January 17, 2022.
Of the 18,028 maintenance dialysis patients at Dialysis Clinic Inc. facilities during the study period, 15,942 (88%) met inclusion criteria and were included in the analysis. Among the eligible patients, 78.0% (n=12,403) were fully vaccinated by December 18, 2021, 55% (n=6853) with mRNA-1287, 41.0% (n=5132) with BNT162b2, 3.0% (n=368) with Ad26.COV2.S, and 0.4% (n=50) with some combination of vaccines. An additional 3% (n=480) were partially vaccinated (276 with mRNA-1273 and 204 with BNT162b2), and 19% (n=3059) were unvaccinated.
In the overall cohort, mean age was 63 years and mean dialysis vintage was 43 months. Eighty-seven percent of the cohort were receiving in-center hemodialysis, 57% had diabetes, and 26% were considered immunocompromised per Centers for Disease Control and Prevention (CDC) criteria.
There were 1173 documented cases of COVID-19 during the study period. Of those, 70% (n=826) occurred during the Delta variant-dominant period. Overall, 46% of cases of COVID-19 (n=535) occurred among those in the fully vaccinated group. Most of those breakthrough cases (96%; n=511) occurred during the Delta-dominant period; 26% (n=137) of patients with breakthrough cases met CDC criteria for being immunocompromised. Median time to follow-up for all patients was 57 days, including time to infection or censoring point for nonevent cases. Among those diagnosed with COVID-19, median time from being considered fully vaccinated was 153 days.
The COVID-19 case rate was significantly lower among fully vaccinated patients than among those who were unvaccinated: 2.21 versus 3.65 per 10,000 patient-days. Overall, vaccine effectiveness was 45%; mRNA-1273 had the highest vaccine effectiveness at 50%, followed by BNT162b2 at 37%.
Across all vaccination status groups, COVID-19 case rates increased during the Delta variant-dominant period. Case rates were lower among fully vaccinated patients (3.25 vs 6.49 per 10,000 patient-days) with 54% vaccine effectiveness compared with unvaccinated patients. The highest vaccine effectiveness was seen in patients vaccinated with mRNA-1273 (60%).
During the study period, there were 424 hospitalizations or deaths related to COVID-19, including 112 COVID-19-related deaths. Of the 112 deaths, 60 were among unvaccinated patients, five among partially vaccinated patients, and 47 among fully vaccinated patients. Thirty percent (n=33) of the COVID-19-related deaths occurred among immunocompromised patients.
The rates of COVID-19-related hospitalizations or deaths were 1.45 per 10,000 patient-days among unvaccinated patients and 0.78 per 10,000 patient-days among vaccinated patients. For patients who were fully vaccinated, the vaccine effectiveness against hospitalization or death was 53% overall (63% with nRNA-1273 and 39% with BNT162b2).
During the Delta variant-dominant period, COVID-19 case rates and vaccine effectiveness against COVID-19-related hospitalization or death worsened among all vaccination groups. In the model comparing patients by vaccination status, fully vaccinated patients had the lowest case rate per 10,000 patient-days in both the pre-Delta and Delta-dominant periods. In the model comparing vaccination status and vaccine types, patients fully vaccinated with mRNA-1273 had the lowest case rate per 10,000 patient-days and the highest vaccine effectiveness against COVID-19-related hospitalization or death in both the pre-Delta and the Delta-dominant periods.
In a subset of 3202 vaccinated patients with at least one antispike immunoglobulin G (IgG) assessment, there was an association between lower antispike IgG levels and higher case rates per 10,000 patient-days and higher adjusted hazard ratios for infection and COVID-19-related hospitalization or death.
Limitations to the study included the observational design, residual biases, and possible confounding.
“SARS-CoV-2 vaccines were effective in maintenance dialysis patients, reducing the risks of COVID-19 cases and COVID-19-related hospitalization or death during the pre-Delta and Delta variant-dominant periods,” the researchers said. “Further research is needed to evaluate SARS-CoV-2 vaccine effectiveness and the utility of antibody titer monitoring to determine which patients are at the highest risk for COVID-19 and to guide the timing of additional vaccine administration.”
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