This is a summary, written by members of the CITF Secretariat, of:
Walmsley SL, Szadkowski L, Wouters B, Clarke R, Colwill K, Rochon P, Brudno M, Ravindran R, Raboud J, McGeer A, Oza A, Graham C, Silva A, Manase D, Maksymowsky P, Parente L, Dayam RM, Simpson J, Pasculescu A, Gingras AC. COVID-19 vaccine antibody responses in community-dwelling adults to 48 weeks post primary vaccine series. iScience. 2023 Apr 21;26(4):106506. doi: 10.1016/j.isci.2023.106506.
The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.
A CITF-funded study, published in iScience, found that third and fourth vaccine doses yielded significant and durable antibody responses in community-dwelling older Canadians, comparable to the levels observed in younger adults. Additionally, the vaccines were well tolerated, and breakthrough SARS-CoV-2 infections were uncommon and mild. This study was led by Drs. Sharon Walmsley (Toronto General Hospital Research Institute and University Toronto) and Anne-Claude Gingras (University of Toronto), in collaboration with Dr. Allison McGeer (University of Toronto).
- After their first vaccine dose, only 45% of adults over the age of 70 had substantial levels of seropositivityVaccine-induced seropositivity is defined by antibody levels to both spike and receptor binding above threshold., compared to 83% of younger adults (aged 30-50 years). The second dose achieved similar substantial levels of seropositivity in both groups: 98% and 100%, respectively.
- Factors predicting lower antibody responses included a previous cancer diagnosis, having had no doses of the Moderna mRNA vaccine, and older age.
- Median antibody levels declined by 12 and 24 weeks post-second dose, but rebounded with the third dose, in both younger and older adults.
- Generally, lower immune responses were observed in the older cohort compared with the younger cohort. However, at 48 weeks (seven months) after the second dose, when most had already received at least a third dose, antibody levels became comparable in both age groups.
- At 48 weeks post-second dose, having had a positive COVID-19 test and having received any dose of the Moderna vaccine were associated with higher levels of anti-RBD antibodies, based on a regression model. Although comorbidity and age affected antibody responses to the initial vaccines, their impact was not significant after 48 weeks, suggesting that booster doses can overcome their impact on the initial antibody response.
- In the 48 weeks following the second dose, 16% of the older cohort and 29% of younger cohort participants without prior SARS-CoV-2 infection became infected, but no participant required hospitalization or died.
This cohort study recruited a total of 1286 adults (911 aged >70 years and 375 aged 30-50 years), between May and July 2021. Participants were followed up to 48 weeks after their first two doses, through collection of dried blood spots and self-reported questionnaires. At the end of the follow-up, overall, 997 (83%) participants received at least a third dose and 59% of the older cohort received a fourth dose (n=239). In the younger cohort, while 91% had received a third dose, only 3% got a fourth dose.