Article content How effective is a single dose of a COVID vaccine? The U.S. Centers for Disease Control data in the Morbidity and Mortality Weekly Report suggests that one dose is not as good as two doses. However, the Public Health Agency of Canada (PHAC) has stated that only a tiny minority of Canada’s COVID-19 cases involved people who had received only one dose of vaccine, compared with no vaccine. Meanwhile, a study conducted in Qatar suggested that one dose was only 30 per cent effective against COVID-19 variants. If true, that would be disastrous in our current situation. People are understandably confused about just how much protection a single shot of Pfizer’s, Moderna’s, or AstraZeneca’s vaccine truly provides.