Save Normal text size Very large text size It’s been called a game-changer by doctors, and a “guerilla fighter” and “long-jumping Gold medallist” by politicians; it has spread at the shops and at the footy among strangers, infecting families and friends – and friends of friends – before anyone knew something was wrong. The newly evolved Delta variant is rapidly taking over as the fittest form of the coronavirus worldwide, driving resurgences from India to the highly vaccinated Israel and the United States. This winter, it’s sent much of Australia into lockdown. But variants have emerged before, and even outbreaks of Delta have been stamped out. Crucially, vaccines still work against it. So why does this variant have scientists so worried and how is it rewriting our infection control playbook?