Study finds weaker COVID-19 vaccine immune response in older adults

September 15, 2021
Dr. Zabrina Brumme and Dr. Mark Brockman.

A recent study by SFU health scientists found that older adults who received two doses of mRNA vaccine to protect against SARS-CoV-2 – the virus that causes COVID-19 – were found to have weaker immune responses than younger adults.

Available as a pre-print manuscript – which is awaiting peer-review – the study was co-led by Faculty of Health Sciences professors Mark Brockman and Zabrina Brumme, and Dr. Marc Romney of Providence Health Care. The researchers measured antibody responses to SARS-CoV-2 after the first and second dose of an mRNA vaccine in 151 participants (ages 24-98), including healthcare workers, residents of long-term care (LTC) or assisted living settings, and older adults living in the community.

 The researchers also followed participants for up to three months after their second vaccine dose to assess durability of the antibody response.

Their investigation found that older age was independently associated with a weaker immune response, even after sociodemographic, chronic health, and vaccine variables were accounted for. In particular, the amounts of virus-specific antibodies produced as well as the antiviral activities of these antibodies decreased as participant age increased.

“The vaccine-induced antibodies in older individuals were less able to block the interaction between the viral Spike protein and the cellular ACE2 receptor, the protein that allows SARS-CoV-2 to infect cells,” says Brockman. “This suggests that the antibodies produced in older adults after vaccination were not as functional as those in younger adults.”

The researchers also looked at the durability of vaccine responses over time and observed that, just three months after completing the two-dose vaccine series, antibody activity had already waned considerably in all participants, regardless of age.

While the rate of antibody decline appeared to be similar for the younger and older groups, the finding was nevertheless concerning. "Because the vaccine-induced immune responses of older adults were less robust than those of younger adults to begin with, this decline suggests that older adults may become susceptible to the virus sooner, as the vaccine’s effects wear off," says Brumme.  

The team's observations add to a growing body of similar evidence emerging from studies worldwide. Awareness of the greater vulnerability of older adults to severe COVID-19 outcomes is leading this group of researchers, along with many others, to highlight older adults as a group who might benefit from receiving a “booster shot” of mRNA vaccine.

Brockman, Brumme and Romney have shared their findings with medical leadership at the local, provincial and national levels, where deliberations on whether to issue an official recommendation for an additional vaccine dose for this age group are continuing. Jurisdictions such as Alberta have already made such boosters available for LTC residents, while BC’s Provincial Health Office is currently collecting data to determine the best interval for additional vaccinations.

While the pandemic is far from over, research, policy and clinical practice continue to develop and roll out rapidly in real-time, offering the best evidence available in the given moment, and improving our understanding of and ability to develop solutions to control COVID-19.

This research is part of a $1.2M grant from the national COVID-19 Immunity Task Force(CITF) that is supporting the investigations of a collaborative team investigating vaccine-induced immune responses.