Just as the long-awaited easing of Covid-19 health restrictions kicked in after more than two weeks of zero local cases, a Hong Kong resident with no travel history has come down with a more infectious strain, possibly the city’s first locally transmitted Delta variant case. Not only has it dashed hopes of an early reopening of borders with the mainland and Macau, but also there are doubts whether it is time to relax social-distancing and quarantine rules. The immediate lockdown on Wednesday of a Tai Po residential block where the man lives for overnight mandatory virus tests underlines the severity of the matter. The tests were also extended to eight premises, including the international airport and a shopping centre where the 27-year-old worked. Separately, the detection of a high viral load in neighbourhood sewage samples prompted another test order covering a wider area. While results in the lockdown operation have all proved negative and provided some relief, those regarding close contacts of the patient and the wider tests are still pending. Authorities are investigating whether the airport ground service worker, who had not been vaccinated, contracted the mutant strain from aircrew members. But the emergence of local infections after a 16-day break suggests there may still be hidden transmission chains in the community. A cluster involving three members of a family in Tuen Mun earlier did not result in a wider outbreak, thanks to the authorities’ more aggressive contact tracing and quarantine controls that saw 30,000 people tested and 140 others put into isolation. Nothing short of that magnitude is needed if we are to successfully curb the spread again this time. The latest case means Hong Kong has yet to go 28 consecutive days without infection to enable quarantine-free travel with Macau. Not only will it inevitably delay the reopening with the neighbouring city, but also most likely with the mainland as well. With several health restrictions currently being eased and hotel quarantines soon to be relaxed, the last thing we need is another serious outbreak. The need to review relaxation measures and put some on hold should therefore be seriously considered.