Vaccine Effectiveness Against SARS-CoV-2 Infection and Severe Outcomes in the Maintenance Dialysis Population in Ontario, Canada

Abstract

Background: Vaccination studies in the hemodialysis population have demonstrated decreased antibody response compared with healthy controls, but vaccine effectiveness for preventing SARS-CoV-2 infection and severe disease is undetermined.

Methods: We conducted a retrospective cohort study in the province of Ontario, Canada, between December 21, 2020, and June 30, 2021. Receipt of vaccine, SARS-CoV-2 infection, and related severe outcomes (hospitalization or death) were determined from provincial health administrative data. Receipt of one and two doses of vaccine were modeled in a time-varying cause-specific Cox proportional hazards model, adjusting for baseline characteristics, background community infection rates, and censoring for non-COVID death, recovered kidney function, transfer out of province, solid organ transplant, and withdrawal from dialysis.

Results: Among 13,759 individuals receiving maintenance dialysis, 2403 (17%) were unvaccinated and 11,356 (83%) had received at least one dose by June 30, 2021. Vaccine types were BNT162b2 (n=8455, 74%) and mRNA-1273 (n=2901, 26%); median time between the first and second dose was 36 days (IQR 28-51). The adjusted hazard ratio (HR) for SARS-CoV-2 infection and severe outcomes for one dose compared with unvaccinated was 0.59 (95% CI, 0.46 to 0.76) and 0.54 (95% CI, 0.37 to 0.77), respectively, and for two doses compared with unvaccinated was 0.31 (95% CI, 0.22 to 0.42) and 0.17 (95% CI, 0.1 to 0.3), respectively. There were no significant differences in vaccine effectiveness among age groups, dialysis modality, or vaccine type.

Conclusions: COVID-19 vaccination is effective in the dialysis population to prevent SARS-CoV-2 infection and severe outcomes, despite concerns about suboptimal antibody responses.

Keywords: COVID-19; Ontario; SARS-CoV-2; chronic dialysis; hospitalization; maintenance; mortality.

Graphical abstract

Figure 1.

Receipt of the first and second dose of the coronavirus disease 2019 (COVID-19) vaccines in the maintenance dialysis population over time plotted against a background of COVID-19 cases in the general population in Ontario, Canada. First and second doses are plotted in yellow and green, respectively. Cases in the general population are plotted in gray. The majority of vaccination occurred during the third wave of the pandemic in Ontario, Canada. The population was followed until June 30, 2021.

Figure 2.

Vaccine effectiveness by age group, dialysis modality, and vaccine type. Vaccine effectiveness was adjusted for age, sex, ethnicity, location, comorbidities, income quintiles, residence in a long-term care facility, years on dialysis, number of RT-PCR tests before December 21, 2020, and background community infection rates.