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

Keeshan A, Galipeau Y, Heiskanen A, Collins E, McCluskie PS, Arnold C, Saginur R, Booth R, Little J, McGuinty M, Buchan CA, Crawley A, Langlois MA, Cooper C. Results of the Stop the Spread Ottawa (SSO) cohort study: a Canadian urban-based prospective evaluation of antibody responses and neutralization efficiency to SARS-CoV-2 infection and vaccination. BMJ Open. 2023 Oct 31;13(10):e077714. doi: 10.1136/bmjopen-2023-077714.

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 BMJ Open, offers yet more evidence that COVID-19 vaccines are safe and effective. The study looked at the initial two COVID-19 vaccine doses and found they were safe, well-tolerated, and highly immunogenic across a broad spectrum of vaccine recipients, including those working in public-facing environments. The study was led by Dr. Curtis Cooper in collaboration with CITF-funded researchers Drs. Marc-Andre Langlois, Arianne Buchan, and Angela Crawley (all from University of Ottawa).

Interesting information about the cohort:

  • The study used blood samples and post-vaccination data from 930 participants among the 1,112 that had enrolled and 1,034 participants for whom baseline data were analysed. Among the 930 participants included in the final analysis, 22.8% had COVID-19 prior to the first vaccine dose and were designated the convalescent cohort. The remainder constituted the surveillance cohort. Over the course of the study 20.9% of the surveillance cohort had at least one new SARS-CoV-2 infection, compared to 10% of the convalescent group.
  • Baseline data showed that participants had a median age of 44, 67% were women, 89% white, 87% Canada-born, 83% employed, 65% earned at least $90,000 annually, and 64% had obtained an undergraduate or advanced degree. A high proportion of participants (63%) were engaged in public-facing occupations, including health care and dental care personnel, air travel cabin crew, teachers, and day care staff. Overall, 38% reported two or more comorbidities, and 31% reported immune-compromising condition(s). Those with a history of prior COVID-19 infections at baseline were older (mean age 46.8 vs 44.4 years) and more likely to be obese (19.1% obese vs 12.6%) than those without prior infection.
  • At the time of data analysis, 98.5% and 97.7% of participants had received at least one or two vaccine doses, respectively, and 70.9% had received one or more booster shot(s). Most participants (87.4%) were vaccinated with mRNA vaccines. The median days between the first and second COVID-19 vaccine doses was 58 and ranged from 11 to 344 days. The length of time in days between the second and third vaccine doses was 185.

Key findings:

  • Over 95% of participants had detectable IgG levels against the spike and receptor binding domain (RBD) three months after the second vaccine dose.
  • The higher a participant’s age and the more immune compromised they were, the lower the IgG spike and RBD titers at month three after the second dose.
  • IgG spike and RBD titers were higher immediately post-vaccination in those who had had a SARS-CoV-2 infection prior to their first vaccine.
  • Spike titers were higher at six months in those with wider time intervals between first and second doses.
  • IgG spike and RBD titers and neutralization were generally similar among people by sex, weight, and whether they had received the same or different vaccine type combinations.
  • Common symptoms after the first vaccine dose included fatigue (65%), injection site pain (48%), headache (27%), fever/chills (26%), and body aches (25%). These symptoms were similar with subsequent doses.

Stop the Spread Ottawa (SSO) is a prospective, longitudinal, cohort study investigating immune responses to SARS-CoV-2 infection and vaccination. Recruitment began on September 14, 2020, and was completed on September 28, 2021. Enrolled participants were followed for 10 months with the option to extend for an additional 24 months.