A single standard dose of vaccine provided 76% protection overall against symptomatic covid-19 in the first 90 days after vaccination with protection not falling in this time frame. It is not clear, however, how long protection might last with a single dose as there were too few cases after 90 days to make any meaningful judgment.
The analyses suggest that it is the dosing interval and not the dosing level which has the greatest impact on the efficacy of the vaccine. This is in line with previous research supporting greater efficacy with longer intervals with other vaccines such as influenza and Ebola.
The study found vaccine efficacy reached 82.4% after a second dose in those with a dosing interval of 12 weeks or more (95% confidence interval 62.7% to 91.7%). If the two doses were given less than six weeks apart the efficacy was only 54.9% (CI 32.7% to 69.7%).