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

Mwimanzi FM, Lapointe HR, Cheung PK, Sang Y, Yaseen F, Umviligihozo G, Kalikawe R, Datwani S, Omondi HF, Burns L, Young L, Leung V, Ennis S, Agafitei O, Basra S, Lim LY, Ng K, Pantophlet R, Brumme CJ, Montaner JSG, DeMarco M, Holmes D., Simons J, Niikura M, Romney MG, Brumme ZL, Brockman MA. Older Adults Mount Less Durable Humoral Responses to a Two-dose COVID-19 mRNA Vaccine Regimen, but Strong Initial Responses to a Third Dose. medRxiv. 2022 Jan 06. doi: 10.1101/2022.01.06.22268745

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

While two doses of COVID-19 vaccine can prevent serious illness in most cases, vaccine-induced immune responses decline naturally over time, which leads to an increased risk of breakthrough infections. A pre-print, not-yet peer-reviewed, from CITF-funded researchers Dr. Mark Brockman of Simon Fraser University, Dr. Zabrina Brumme of Simon Fraser University and the BC Centre for Excellence in HIV/AIDS, and Dr. Marc Romney, from Providence Health Care and the University of British Columbia, showed that a third (booster) dose of vaccine elevated both the levels of antibodies and their neutralizing capacity above that of two doses in all individuals, including older adults.

The study characterized antibody responses over time in younger adults (healthcare workers with a median age of 41 years) and older adults (including residents of long-term care homes with a median age of 78 years), between one and six months after the second vaccine dose, and one month after the (third) booster dose.

Key points:

  • A previous peer-reviewed publication[1] from this group showed that one month after the second vaccine dose, the level of antibodies specific to the spike receptor-binding domain (RBD) of SARS-CoV-2 was lower in the blood of older adults compared to younger adults. The ability of these antibodies to neutralize SARS-CoV-2 was also weaker in the older adults.
  • This new study found that six months after the second dose, antibody levels had declined further in all participants. At six months following the second dose, the neutralizing activity of these antibodies had declined to undetectable levels in more than half of the study participants, including 60% of younger adults and 87% of older adults.
  • The faster rates of antibody decline were observed in older adults. This suggests that in addition to mounting overall weaker responses to COVID-19 vaccination, binding antibody responses in older adults also wane more quickly. Each chronic condition, which accumulate with age, was showed to further shorten the antibody half-life.
  • In contrast, the researchers observed that antibody binding, as well as the antibodies’ neutralizing abilities and responses, waned the slowest in individuals who received two doses of a COVID-19 vaccine after having recovered from COVID-19 disease. This is consistent with reports that COVID-19 followed by vaccination produces particularly durable immune responses.
  • Importantly, a third COVID-19 vaccine dose boosted the concentration of RBD-binding antibodies as well as the neutralization activities of these antibodies to higher levels than those seen after two doses, in all individuals.

The evidence supports the importance of booster doses for both younger and older adults. However, booster doses in older adults and people with pre-existing medical conditions should be prioritized.

[1] Brockman MA, Mwimanzi F, Lapointe HR, Sang Y, Agafitei O, Cheung P, Ennis S, Ng K, Basra S, Lim LY, Yaseen F. Reduced magnitude and durability of humoral immune responses by COVID-19 mRNA vaccines among older adults. medRxiv. 2021 Jan 1.