This is a summary, written by members of the CITF Secretariat, of:

Yau K, Chan CT, Abe KT, Jiang Y, Atiquzzaman M, Mullin SI, Shadowitz E, Liu L, Kostadinovic E, Sukovic T, Gonzalez A, McGrath-Chong ME, Oliver MJ, Perl J, Leis JA, Bolotin S, Tran V, Levin A, Blake PG, Colwill K, Gingras AC and Hladunewich MA. Differences in mRNA-1273 (Moderna) and BNT162b2 (Pfizer-BioNTech) SARS-CoV-2 vaccine immunogenicity among patients undergoing dialysis. CMAJ February 03, 2022 cmaj.211881; doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

CITF-funded researchers Drs. Michelle Hladunewich and Matthew Oliver from Sunnybrook Health Sciences Centre compared antibody responses after two-dose COVID-19 immunization with mRNA vaccines in individuals undergoing hemodialysis. They found that at 6–7 weeks after the second dose, those who received Moderna’s Spikevax elicited higher antibody levels than Pfizer-BioNTech’s Comirnaty. Further, those vaccinated with Moderna sustained their antibody levels more than did those who received Pfizer, when measured 12 weeks after the second dose. The study is published in the Canadian Medical Association Journal.

A total of 224 participants undergoing hemodialysis Hemodialysis is a medical procedure used to filter waste from the blood when the kidneys are no longer healthy enough to do this work.  were followed between February 2 and July 20, 2021 in Toronto. Of these, 129 received two doses of the Pfizer-BioNTech Comirnaty vaccine and 95 received Moderna Spikevax. None had a mixed mRNA vaccine series.

Blood was collected and tested for antibody levels against the SARS-CoV-2 spike protein, receptor binding domain (RBD), and nucleocapsid at 6-7 weeks and 12 weeks following the second dose.

Key findings:

  • No serious adverse effects following vaccination were reported among participants.
  • At 6-7 weeks post second dose, median spike antibody levels were significantly higher for those vaccinated with Moderna than Pfizer; the levels of RBD antibodies did not differ substantially between groups.
  • At 12 weeks post second dose, spike antibody levels had waned more in those who received Pfizer compared to Moderna. At this timepoint, RBD antibody levels were also lower in participants vaccinated with Pfizer compared to Moderna.
  • During the study period, three patients who were double vaccinated with Pfizer had a laboratory confirmed SARS-CoV-2 infection. No participant who received Moderna contracted SARS-CoV-2.

Other studies have seen similar differences in antibody responses between mRNA vaccine products, though the functional mechanism behind these observations is not yet clear. It should be noted that the vaccines contain different mRNA concentrations: Moderna has 100 micrograms1 of mRNA, whereas Pfizer has 30 micrograms.

In light of these results, the authors recommended that individuals undergoing dialysis obtain a third (booster) dose of vaccine. This research  directly contributed to the National Advisory Committee on Immunization guideline issued In October 2021, that individuals with moderate to severe immunosuppression, which includes those with chronic kidney disease requiring dialysis, be vaccinated with a third (booster) dose of an mRNA vaccine.

The study team has previously published antibody results following one dose of mRNA vaccine. You can find that summary here.

1 Booster doses of Moderna contain half the concentration of mRNA (50 micrograms).