Residents of one Southwest Sydney council area will be subject to a strict new coronavirus rule as the city grapples with a serious outbreak. The chief executive of medical research body Burnet Institute said stage four restrictions would need to be in place for another four weeks with Sydney’s outbreak worsening. Mr Crabb claimed that was because an unmitigated Delta strain worsened exponentially when compared with other strains of the virus. “I'm afraid so,” Mr Crabb said when asked about a four-week lockdown extension for Sydney. “But for Delta, one case turns into 50,000 cases; 50 times worse.