Immunogenicity and safety of COVID-19 vaccine Co-administration and Interval in Immunocompromised hosts (CO2I2 Trial).

Persons with weakened immune responses, including those who received transplants, live with human immunodeficiency viruses, have inflammatory bowel diseases, primary immunodeficiencies, or systemic autoimmune diseases are at an increased risk for experiencing airway infections and have more severe complications than the general population. During the recent COVID-19 pandemic, persons with weakened immunity were particularly vulnerable to experience disruptions to their lifestyle, more severe complications, and death. This is related, at least in part, to decreased ability to develop a protective immune response to vaccines. A stronger protective immune response to vaccines may be lifesaving for these patients, but there is limited information on how to optimize them, especially with periodic influenza activity reported in regions across Canada. The CO2I2 trial will try to address this concern by considering two strategies for improved protection thanks to vaccines targeting airway infections from Influenza and SARS-CoV-2. The first question is "can we improve vaccine uptake and protective effects by giving COVID-19 and seasonal flu vaccines together or one after the other?", and the second question is "what is the preferred time gap between two consecutive COVID-19 vaccine doses that results in better protection?" Improving protection against airway infections will improve the health and quality of life of persons with weakened immunity and potentially will decrease likelihood of future healthcare emergencies. Verifying the protective effect of and absence of complications related to administration of vaccines against respiratory infections as outlined in our study is likely to protect immunocompromised persons from experiencing serious infection, improve their quality of life and decrease burden to care takers and the health care system.