THE eight local government areas in hard lockdown, on top of the existing Greater Sydney restrictions, combine to form a single cross-shaped area, from just south of Windsor to just north of Appin, and just from west of Botany Bay to just east of Blue Mountains National Park. That's some 1270 square kilometres all up, and home to more than 2 million people. With the Greater Sydney restrictions in place until at least August 28, and with yesterday's case total of 170 still too high for comfort, the federal government has responded to a call from NSW Police for Australian Defence Force personnel. Defence Minister Peter Dutton has confirmed that up to 300 "Defence members" will work in Sydney under police control from Monday. It's not the first time the military has been involved in COVID work. The NSW government says the military's tasks will include door-knocking to ensure that COVID-positive people are complying with stay-at-home requirements. Ten days ago the ADF said 65 per cent of its personnel had received one shot, with more than 40 per cent fully vaccinated. Yesterday, NSW Police Commissioner Mick Fuller conceded there was no formal requirement that the door-knockers be vaccinated. Chief Health Officer Kerry Chant played down the infection risks. But the quarantine system has proved far from foolproof. This outbreak began, after all, with a single unvaccinated limousine driver ferrying international flight crews between Sydney Airport and their quarantine hotels. It would be better to have home quarantining monitored by vaccinated people. Admittedly, there's a small chance of someone vaccinated contracting COVID. Such people can also transmit the virus. These "breakthrough" cases are generating debate in hard-hit countries, and have been wrongly highlighted by anti-vaxxers to spread doubt about our best protection against the virus. Rarities, yet, in Australia, the US recorded more than 10,200 cases among 101 million fully inoculated people by the end of April. Breakthrough rates have risen with Delta, leading the Biden administration's determination to get even vaccinated people back behind masks. Not great news, but to quote from a leaked US Centres For Disease Control and Prevention document, "the war has changed". So, then, must the battle plans.