Australia has doubled its order of the Pfizer Inc Covid-19 vaccine, Prime Minister Scott Morrison said, as the country raced to overhaul its inoculation plan over concerns about the risks of blood clots with the AstraZeneca Plc vaccine.

Until late Thursday, Australia based its vaccination programme largely on AstraZeneca shot, with an order for 50 million doses — enough for the required two shots for its entire 25 million population — to be made domestically by biopharma CSL Ltd.

But Australia has now joined a host of countries in restricting use of the vaccine due to clotting concerns. Local health authorities have changed their recommendation to say the country's nearly 12 million people aged under 50 should take the Pfizer product instead, according to Reuters.

As a result Australia has doubled an earlier Pfizer order to 40 million shots, enough for four-fifths of the population, which would be delivered by the end of the year, Morrison said.