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

Breznik JA, Zhang A, Huynh A, Miller MS, Nazy I, Bowdish DME, Costa AP, COVID-in-LTC Study Group. Antibody responses 3-5 months post-vaccination with mRNA-1273 or BNT163b2 in nursing home residents. medRxiv. 19 Aug 2021. Doi: https://doi.org/10.1101/2021.08.17.21262152

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

In a recent CITF-funded study, not yet peer-reviewed, researchers from McMaster University Dr. Andrew Costa and Dr. Dawn Bowdish, in collaboration with the COVID in Long Term Care Study Group, examined immunity responses to COVID-19 vaccines in nursing home residents after two doses of Moderna or Pfizer-BioNTech vaccines. They found that most seniors elicited an initial antibody response and that Moderna offered a stronger antibody response than Pfizer.

Their findings were based on blood draws from 138 long-term care residents in Ontario between March and July 2021.

Key Points:

  • The majority of residents (97.1%) produced an initial immune response shown by the presence of antibody levels and their sera had the capacity to neutralize the virus.
  • In about 20% of nursing home residents, two doses of vaccine failed to elicit an effective antibody response against the original wild-type SARS-CoV-2 virus (the original strain) and the Beta variant.
  • Although the Pfizer vaccine elicited antibody responses among participants, vaccination with the Moderna vaccine elicited a higher antibody levels in residents when compared to Pfizer.

The findings from this study are in line with previous results that show decreased antibody production and lower neutralizing antibody levels after vaccination among older adults. Given that the Moderna vaccine contains a higher concentration of mRNA (100 micrograms compared to 30 micrograms for Pfizer), the authors suggest that this higher dose may be advantageous in developing protective immunity in long-term care residents. The authors propose that vaccine type be considered when planning vaccine campaigns among older adults to potentially reduce breakthrough infections. This is in line with another recent CITF-funded study led by Drs. Allison McGeer, Anne-Claude Gingras and Sharon Straus that shows a subtle difference in antibody response between the two mRNA vaccines among older Canadians.