Covid: Why Australia's 'world-class' quarantine system has seen breaches

Australia's hotel quarantine system has been an extremely effective first line of defence against Covid-19. The country has largely eliminated the virus, often going weeks without a locally acquired infection. Hotel quarantine is credited a huge part of that success. But a series of isolated local cases in recent months - all from hotel quarantine leaks - have caused alarm. Since November, three cities have entered snap lockdowns on the back of such infections, aiming to halt outbreaks at their source. But how does the virus keep slipping through what officials hail as a 'world-class' first defence?