New data stemming from a study in British Columbia evaluating the strength and magnitude of antibody responses following one dose of the Pfizer-BioNTech vaccine indicate that older adults generate a much weaker antibody response to one vaccine dose compared to younger adults. These findings (in preprint and therefore not yet peer reviewed) hail from a CITF-funded project led by Dr. Marc Romney at the University of British Columbia, and Drs. Zabrina Brumme (BC Centre for Excellence in HIV/AIDS) and Mark Brockman (Simon Fraser University).


It has been well recognized that older individuals are at greatest risk of severe outcomes following SARS-CoV-2 infection. Protecting this vulnerable population has therefore been the priority of Canada’s COVID-19 immunization program since December 2020. However, researchers are only now starting to understand the immune response following vaccination in this critical age group. Dr. Romney and his team have focused their research efforts on individuals living and working in long-term care and assisted living facilities, groups which have by far experienced the most serious consequences of the COVID-19 pandemic. Indeed, the participants included in this study are part of a larger ongoing study in Vancouver-area long-term care facilities that aims to provide a detailed picture of the immune responses in long-term care residents and staff following SARS-CoV-2 infection, COVID-19 vaccination, or both.

Immediately after enrolling in the study and at baseline, participants were tested for SARS-CoV-2 antibodies (antibodies would suggest a past infection with the virus). Researchers investigated blood samples from 12 long-term care residents aged 75 and over, and 18 healthcare workers working in long-term care, with a median age of 36. None of these participants had SARS-CoV-2 infection before their vaccine. The team also included blood samples from four healthcare workers, with a median age of 44, who had recovered from COVID-19. Blood samples were collected from all participants between the end of December 2020 and the beginning of January 2021, before vaccine roll-out, and again between the end of January and the beginning of February 2021, following their first dose of Pfizer-BioNTech mRNA-based COVID-19 vaccine.

In a series of sophisticated experiments, the research team studied the blood samples to assess the level and strength of participants’ antibody responses before and after one dose of the COVID-19 vaccine. Specifically, they focused on measuring the ability of vaccine-induced antibodies to both bind to their desired target and block viral infection. Overall, the authors found that the antibody response produced in older adults was drastically lower and less robust than in younger adults. More specifically, they found that the vaccine-induced antibodies in older adults were not nearly as good at blocking a SARS-CoV-2 infection.

“Results from this study reveal that individuals of advanced age, following the first dose of a two-dose vaccination regimen, are less able to generate as strong an antibody response, both in terms of magnitude and function, compared to adults of younger age,” states Dr. Romney. “It will be important to assess whether this observation extends to older persons living in the community as this may inform the optimal timing of the second dose for this population.” These results suggest that despite a first dose of vaccine, we must remain vigilant for people aged 75 and up.

In parallel, researchers showed that in a group of four healthcare workers previously infected with the virus, antibody levels soared following one vaccine dose and their antibodies showed good proficiency in blocking the virus. These findings add to the mounting evidence demonstrating that a single dose of vaccine provides strong protection for younger people who have recovered from COVID-191,2 (read more about this phenomenon here).


Mark A Brockman, Francis Mwimanzi, Yurous Sang, Kurtis Ng, Olga Agafitei, Siobhan Ennis, Hope Lapointe, Landon Young, Gisele Umviligihozo, Laura Burns, Chanson J Brumme, Victor Leung, Julio S G Montaner, Daniel Holmes, Mari DeMarco, Janet Simons, Masahiro Niikura, Ralph Pantophlet, Marc G Romney, Zabrina L Brumme. Weak humoral immune reactivity among elderly residents of long-term care facilities following one dose of BNT162b2 mRNA COVID-19 vaccine. medRxiv 2021.03.17.21253773; doi:

  1. Manisty, C. et al. Antibody response to first BNT162b2 dose in previously SARS-CoV-2-infected individuals. Lancet 397, 1057-1058, doi:10.1016/s0140-6736(21)00501-8 (2021).
  2. Saadat, S. et al. Binding and Neutralization Antibody Titers After a Single Vaccine Dose in Health Care Workers Previously Infected With SARS-CoV-2. Jama, doi:10.1001/jama.2021.3341 (2021).