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

Brockman MA, Mwimanzi F, Lapointe H, Sang Y, Agafitei O, Cheung P, Ennis S, Ng K, Basra S, Lim LY, Yaseen F, Young L, Umviligihozo G, Omondi FH, Kalikawe R, Burns R, Brumme CJ, Leung V, Montaner JSG, Holmes D, DeMarco M, Simons J, Pantophlet R, Niikura M, Romney MG, Brumme ZL. Reduced magnitude and durability of immunity elicited by COVID-19 mRNA vaccines among older adults. Doi: 10.1101/2021.09.06.21263149v1

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

In a recent CITF-funded pre-print, therefore not yet peer-reviewed, Drs. Mark Brockman and Zabrina Brumme from Simon Fraser University and Dr. Marc Romney from the University of British Columbia studied immune responses following COVID-19 vaccination in over 150 adults aged 24-98 years. They found that although two doses of the mRNA vaccines provide excellent protection against SARS-CoV-2, significantly weaker vaccine-induced immune responses were recorded among older adults. They also found that immune responses waned in everyone, regardless of age, after only three months following the second vaccine dose.

The magnitude of SARS-CoV-2-specific antibody response after one and two doses of an mRNA vaccine was studied in 151 participants. These included 89 healthcare workers (HCW) (median age of 41) as well as 62 older adults (median age of 79), of which 23 were long-term care (LTC) residents or living in assisted living facilities, and 39 were seniors living in the community. Due to limited vaccine supply earlier this year, the British Columbia public health authorities had extended the interval between the first and the second doses of the COVID-19 vaccine during the study period. Participants had therefore received their second dose an average of 91 days after the first dose (range of 70 to 99 days).

Key points:

  • Older adults showed significantly weaker vaccine immune responses at all time points tested
  • One month following the second dose, samples of 15 HCWs were tested with stringent live-virus neutralization assays, and all (100%) displayed the ability to block viral infection. In comparison, only 11 of 17 samples from older adults displayed the ability to block viral infection.
  • Three months following the second dose, immune responses had waned in participants of all ages.
  • The immune response in older adults was also significantly weaker when faced with the Delta variant.

The humoral immune response to COVID-19 mRNA vaccines is significantly weaker in older participants, who could potentially benefit from additional immunizations or boosters. Indeed, recent COVID-19 outbreaks among immunized individuals living in LTC facilities underscores the ongoing risk among this priority population.

These results reinforce several other recent CITF-funded publications. The complete description of all the CITF-funded vaccine surveillance research studies looking at seniors across Canada can be accessed here.