Aus­tralia has secured a deal with the drug­mak­er AstraZeneca to sup­ply a poten­tial Covid-19 vac­cine to its entire pop­u­la­tion free of charge, the gov­ern­ment announced Tues­day, becom­ing the lat­est coun­try to lock in sup­plies of the drug should tri­als succeed.