In a CITF-funded study originally released as a preprint and now published in the Journal of Infectious Diseases, Drs. Mark Brockman and Zabrina Brumme from Simon Fraser University and Dr. Marc Romney from the University of British Columbia examined immune responses following COVID-19 vaccination in over 150 adults aged 24-98 years. They found that although two doses of the mRNA vaccines induced readily detectable antibody responses against SARS-CoV-2 in nearly all people, these responses were significantly weaker among older adults. They also found that antibody responses in blood declined during the first three months following the second vaccine dose, regardless of age, and remained significantly lower among older adults over time.

The magnitude and durability of SARS-CoV-2-specific antibody responses after one and two doses of an mRNA vaccine was studied in 151 participants. These included 89 healthcare workers (HCWs) (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 in early 2021, the British Columbia public health authorities had extended the interval between the first and second dose 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-induced antibody responses at all time points tested. Older age was an independent predictor of lower responses, even after correcting for other factors including chronic health conditions.
  • One month following the second dose, 98% of HCWs displayed the ability to block SARS-CoV-2 infection when tested using stringent live-virus neutralization assays. In comparison, 85% of older adults displayed the ability to block viral infection.
  • Three months following the second dose, antibody responses had declined in participants of all ages and remained significantly lower in older adults. At this time, 81% of HCWs displayed the ability to block SARS-CoV-2 infection, compared to 52% of older adults.
  • The anti-receptor binding domain antibody response in older adults was approximately two-fold weaker when faced with the Delta variant compared to the HCWs.

While antibody responses measured in blood may not be fully predictive of protection against disease, this study underscores the ongoing risk of SARS-CoV-2 infection in older adults and it provides additional support for booster doses that are now being rolled-out across Canada in 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.

Brockman MA, Mwimanzi F, Lapointe HR, 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 ML, Simons J, Pantophlet R, Niikura M, Romney MG, Brumme ZL. Reduced magnitude and durability of humoral immune responses to COVID-19 mRNA vaccines among older adults. J Infect Dis. 2021 Dec 9. doi: https://doi.org/10.1093/infdis/jiab592