One dose of mRNA vaccine reduced COVID risk for at least four months in health care workers Due to a shortage in vaccines, the Quebec Immunization Committee (QIC) recommended that the Canadian province of Quebec defer the second dose of the coronavirus disease 2019 (COVID-19) vaccine to optimize the coverage of the first dose. The reason behind this proposal was to protect a majority of the high-risk population, which includes individuals in the older age groups and frontline workers, from severe COVID-19 infection and deaths. Quebec started its vaccination campaign by targeting long-term care facility (LTCF) residents and healthcare workers (HCW) who were in direct contact with patients. Based on the vaccine supply and short-term vaccine effectiveness (VE) reports, in early March 2021, the Canadian National Advisory Committee on Immunization and the Quebec Ministry of Health set the duration between two vaccine doses to be 16 weeks.