"As long as there are flights returning citizens to Australia, elimination of COVID-19 is impossible.
"Every day we see cases emerge in hotel quarantine around the country, including in Western Australia."
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NSW reported three new local cases during the 24 hours to 8pm on Sunday, all in a family linked to the Berala cluster.
However, two mystery cases were identified after the reporting period: a western Sydney couple whose infections were discovered after one attended Mount Druitt Hospital emergency department with symptoms on the weekend.
In September, the national hot spot definition of a rolling three-day average of three cases a day was presented as a way for states to decide when to close borders. However, many have not used this definition, which itself has become murky in recent weeks.