The variant, first detected in India in December last year, has spread to about 100 countries and the World Health Organization warned recently that it could soon become the dominant form of the virus. It is also driving a spike in cases in Japan, casting a pall over this month's Olympic Games.

On Friday, Australia's New South Wales state, its most populous, reported the biggest daily rise in new cases so far this year. Total cases in the state in the latest outbreak have topped 200, a majority caused by the Delta variant.

Sydney, home to a fifth of the country's 25 million population, is half-way through a two-week lockdown to contain the outbreak, which has alarmed authorities amid a sluggish nationwide vaccination drive.

"I think the vaccine will certainly reduce the disease, it will certainly reduce hospitalization. But we'll certainly have the virus circulating in the community for those people who aren't vaccinated," said Professor Jill Carr, a virologist with the College of Medicine and Public Health at Flinders University.

Australia, like several other countries in Asia, has struggled to inoculate people as initial successes in containing the pandemic led to vaccine hesitancy, and manufacturers were slow to ship doses.

Australia has fully vaccinated only 6 percent of its population, while Japan has vaccinated 12 percent.

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