Low antibody levels after one dose of the Pfizer-BioNTech vaccine in hemodialysis patients

The risk of death from COVID-19 for patients receiving hemodialysis is 25% – much higher than in the general population. One of the reasons for this is that hemodialysis patients have compromised immune systems. Patients receiving hemodialysis were not included in the Pfizer-BioNTech clinical trials, so it is unclear if these patients develop strong immune responses following vaccination. In a recent article published in Canadian Medical Association Journal (CMAJ), CITF-funded researcher Dr. Andrés Finzi from Université de Montréal, lead author Dr. Rita Suri from McGill University, and a larger research team, report that antibody responses after the first dose of the Pfizer vaccine in hemodialysis patients are reduced compared to healthy controls. They will be following these subjects to see if immune responses improve after the second dose.

Key Points:

• Hemodialysis patients without previous SARS-CoV-2 infection had much lower antibody levels after vaccination compared to a control group of healthcare workers (not on hemodialysis). The antibody levels were also lower than antibody levels from convalescent plasma taken from hemodialysis patients who had survived natural COVID-19 infection.
• Hemodialysis patients with a history of COVID-19 developed antibody levels similar to controls eight weeks after vaccination.
• Researchers recommend that the second dose of the Pfizer vaccine be administered to patients receiving hemodialysis three weeks later, at the manufacturer-recommended time interval.

Hemodialysis patients (n=154) were recruited from the Réseau Rénal Québécois/Quebec Renal Network (RRQ/QRN) COVID-19 study. Patients with and without a previously documented SARS-CoV-2 infection were included. Additionally, a total of 40 healthcare workers, with or without a previous SARS-CoV-2 infection, were recruited as controls. Blood samples from hemodialysis patients who had recovered from COVID-19 (unvaccinated) were also collected as controls. Researchers wanted to determine how the antibody responses differed among the different groups after a single dose of the Pfizer vaccine.

Among hemodialysis patients who had not had a previous SARS-CoV-2 infection, researchers observed significantly lower levels of antibodies against SARS-CoV-2 at both four- and eight-weeks post-vaccination compared to the antibody levels in both control groups: healthcare workers at three weeks post-vaccination and hemodialysis patients who had recovered from COVID-19.

Hemodialysis patients who had a previous SARS-CoV-2 infection had significantly lower antibody levels four weeks after vaccination compared to the three-week levels in healthcare workers who had also had previous SARS-CoV-2 infection. However, the antibody levels in hemodialysis patients who had previous infections and were vaccinated were not significantly different to antibody levels found in the blood samples of hemodialysis patients who had recovered from COVID-19 (the other unvaccinated control group). Eight weeks after vaccination, hemodialysis patients who had a previous infection were observed to have similar antibody levels to infected healthcare worker controls at three weeks post-vaccination.

Altogether, this study has demonstrated that a single dose of Pfizer vaccine may fail to elicit an adequate antibody response in most hemodialysis patients without previous SARS-CoV-2 infection. In those with previous SARS-CoV-2 infection, the vaccine-induced antibody response was present, but delayed. Researchers of this study therefore recommended that the second dose of the Pfizer vaccine be administered to patients receiving hemodialysis at the suggested three-week time interval.

Based on these findings, which were published as a preprint on April 1, 2021, the Quebec and Ontario public health authorities recommended shortening the interval between vaccination doses from 16 weeks to four weeks for all patients receiving hemodialysis. These findings were later confirmed in a preprint by Dr. Hladunewich and several CITF members who also reported that poor antibody responses were observed following the first dose of vaccination in hemodialysis patients.

A longitudinal follow-up of this cohort is ongoing and will be essential to determine the degree of humoral and cell-mediated responses induced post-vaccination in hemodialysis patients. (These responses represent an additional layer to the immune response beyond antibodies only.)