This real-world study is addressing the marked and unexpected reduction in the supply of the mRNA vaccines to Canada, as of January 2021, which has led to a policy change of delaying the second dose of the Pfizer vaccine to healthcare workers (HCW) up to 35 to 42 days. There is little evidence to support this policy, which could be harmful if immunity diminishes to low levels, leaving HCWs at risk of infection before the delayed second dose.
Furthermore, there is no data to inform how dosing schedules may impact on the secondary immune responses and long term immunity. However, this policy represents a potential natural experiment and an opportunity to study the impact of dosing schedule on vaccine immunogenicity as it relates to short and long term immunity. Since the sequence and timing interval of dosing to HCWs are largely randomly generated; the variation in time interval between the first and second vaccine doses is unbiased and unaffected by any factors other than by chance.
We therefore propose an opportunistic study in which we will study and address the following questions:
1. Examine the NAb levels and cellular immune responses at days 35-42 compared to day 21 following the first dose of mRNA vaccine.
2. Characterize the profile of NAb and cellular immune responses following the first dose of vaccine up to 42 days and following the second dose up to 12 months
3. Contrast the profiles of NAb and cellular immune responses between 21-day dosing interval (correct cohort) versus delayed 35-42 day dosing (delayed cohort) interval of vaccine.
To explore the threshold levels for NAbs and cellular immunity associated with significant reduction in infection risk of symptomatic SARS-CoV2 infection.
The secondary objective will be exploratory as the study is not powered to examine this objective. The findings will help to guide the planning of a larger study to address this particularly question.
Collaborators include Mark Loeb, Dawn Bowdish, Matthew Miller, Ishac Nazy, Zain Chagla, Jonathan Bramson, and Judah Denburg.TIMING study recruitment poster
Prospective cohort study
MyLinh Duong is a respirologist at Hamilton Health Sciences, and Associate Professor, Department of Medicine, McMaster University. Her research interests include respiratory epidemiology, and understanding the environmental and social determinants of lung development and lung function. She is the respiratory lead for a number of PHRI’s population-based studies including PURE, FAMILY and the global heart failure registry, G-CHF.
She obtained her medical degree, specialist and sub-specialist training in Internal Medicine, Sleep Medicine and Respiratory Medicine at the University of Adelaide, Australia. This was followed by a research fellowship in the areas of airway inflammation, asthma and COPD at the Firestone Clinic and McMaster University, Canada, where she obtained a Master’ degree in Health Research Methodology and Epidemiology.
Darryl Leong is a Scientist at PHRI, Director of the McMaster University and Hamilton Health Sciences Cardio-Oncology Program, Associate Professor, Department of Medicine (Cardiology), McMaster University, and Staff Cardiologist at Hamilton Health Sciences. He has methodological expertise in clinical epidemiology and clinical trials, and content expertise in physical frailty, echocardiography, and cardio-oncology. His research is supported by the CIHR, and he has published more than 100 manuscripts including all the leading internal medical and cardiovascular journals.
He graduated from the University of Adelaide Medical School with Deans Listing and Honours for academic excellence, completed his cardiology training, Doctor of Philosophy, Master of Public Health, and Master of Biostatistics degrees at the University of Adelaide in Australia, and completed a post-doctorate fellowship in cardiovascular imaging at the Leiden University Medical Centre in The Netherlands, before re-locating to Canada.
Sumathy Rangarajan has been Program Director, Global Health, since 2016, preceded by many years’ service at PHRI in other roles. She oversees the PURE study team, as well as the INVICTUS rheumatic AF treatment trial, the CANPWR pediatric weight management registry, and others.
She holds both a Bachelor of Science Degree and a Master of Science degree from Pune University in India.
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