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As COVID-19 vaccine programs continue to roll out, global supply and manufacturing interruptions have led to temporary vaccine shortages. This has led some provinces to change, or consider changing, their vaccine rollout strategy to ensure vaccine programs can continue to operate.

One option when there is a shortage of vaccines is to use two different COVID-19 vaccines for the first and second dose. In this case, if a different vaccine is available it could be used rather than waiting for the same kind of vaccine. Combinations of different vaccines were not used in original clinical trial data and is therefore up to researchers and Public Health to help answer questions that will help address vaccine supply shortages.

A second strategy is to extend the wait between the first and second dose (interval) of an approved COVID-19 vaccine from 4 weeks, as recommended by the manufacturer, to up to 16 weeks. Based on clinical trial evidence that shows high efficacy of a single dose and the benefits of having as many people with at least one dose as possible, this strategy is already in use across Canada.

The objective of the Canadian MOSAIC study is to systematically evaluate these strategies as well to find out how long vaccine protection lasts when these strategies are used.

Currently, four COVID-19 vaccines made by different manufacturers have received regulatory approval in Canada (Pfizer/BioNTech, Moderna, AstraZeneca, and Johnson and Johnson); three are being administered in public health programs (Pfizer/BioNTech, Moderna, AstraZeneca). As additional vaccines become available and begin being distributed, they will be added to the study. The study may also be modified by adding new populations, such as younger age groups or pregnant individuals, over time. The study data will be communicated regularly to public health and the COVID-19 Immunity Task Force to inform decision making during the pandemic.

The study is led by the Clinical Trials Network of the Canadian Immunization Network (CIRN) and funded by the COVID-19 Immunity Task Force. It is led by Dr. Joanne Langley and Dr. Manish Sadarangani.