Findings from a real-world vaccination study composed of seniors residing in long-term care facilities were recently released in preprint, therefore not yet peer-reviewed, on behalf of investigators from the CITF-funded study UNCoVER (including Dr. Donald Vinh, Research Institute of the McGill University Health Centre (RI-MUHC) and Dr. Marc-André Langlois, University of Ottawa) and the CITF Secretariat (Dr. Bruce Mazer, Associate Director, Strategy, affiliated with the MUHC). This study found both Pfizer and Moderna vaccines (or a mix-and-match of each) elicited similar antibody responses four weeks after the second dose.

Older adults residing in long-term care facilities in Quebec, with or without a previously documented SARS-CoV-2 infection, received two doses of an mRNA vaccine (Pfizer-BioNTech’s Cominarty and/or Moderna’s Spikevax) with an extended 16-week interval between doses. This study included individuals who received either two doses of the same vaccine (homologous vaccination) or a mix-and-match regime (heterologous vaccine combination).

Key observations:

  • People who had never had SARS-CoV-2 initially exhibited lower antibody responses after the first dose compared to people who were vaccinated after having previously been infected. However, four weeks after the second dose, both groups achieved comparable levels of antibodies.
  • Four weeks after the second dose, antibody levels were very similar in individuals who had received Cominarty or Spikevax or a combination of the two.

These preliminary results are part of an ongoing longitudinal study. The results indicated that among frail seniors, neither age, nor sex, nor comorbidity affect SARS-CoV-2 antibody production in response to mRNA-based COVID vaccines. The main factors associated with higher antibody responses after one dose of the mRNA vaccine were the type of vaccine (Spikevax performing better) and whether the individual had had a previous SARS-CoV-2 infection. However, when looking at antibody responses four weeks after the second dose, Cominarty and Spikevax (or a mix-and-match of the two) elicited similar  antibody responses, supporting their interchangeability.

Another Quebec-based study, led by CITF-funded researcher Dr. Andrés Finzi from the University of Montreal, also released real-world vaccination results as a pre-print (therefore not yet peer-reviewed), from a general population cohort that received two doses of Cominarty with an extended 16-week interval between doses. This research team also observed comparable levels of SARS-CoV-2 antibodies independent of previous infection post-second dose, supporting the benefits of the extended interval period used.

Vinh DC, Gouin JP, Cruz-Santiago D, Canac-Marquis M, Bernier S, Bobeuf F, Sengupta A, Brassard JP, Guerra A, Dziarmaga R, Perez A, Sun Y, Li Y, Roussel L, Langelier J, Ke D, Arnoldd C, Pelchat M, Langlois MA, Zhang X, Mazer BD. Real-world serologic responses to Extended-interval and Heterologous COVID-19 mRNA vaccination in Frail Elderly-Interim report from a prospective observational cohort study. medRxiv 21 Sept 2021; doi: 10.1101/2021.09.16.21263704