Professor Raina MacIntyre, biosecurity expert from the University of New South Wales told Xinhua that the latest outbreaks in the most populous cities of Australia are a part of a trend of repeated breaches in hotel quarantine in Australia since last year.

"The presence of the more transmissible Delta strain raises the stakes, as if there are undetected chains of community transmission. It will be harder to control than previously," MacIntyre said. READ MORE