Convincing Beijing that Hong Kong’s Covid-19 control measures will not leave gaps in the state’s defences against the pandemic has become a top priority. This has been made more difficult in the wake of a new case involving an airport worker . Even though officials believe talks in reopening the border will not be hampered by the end of the city’s 51-day run of zero local infections, the challenges ahead must not be underestimated. How the cargo handler became infected remains a mystery, but genome-sequencing testing of the virus he carried revealed a close resemblance to infections detected in Britain last month. Separately, a Cathay Pacific aircrew member tested positive for the coronavirus upon arrival in Australia last week. The immediate testing and isolation of those infected shows we do have a mechanism against a wider outbreak. But it also underlines inadequacies in preventing imported infections from spreading to the local community. The case of the cargo worker was the second of its kind at the airport, and follows that of an employee at a VIP lounge in August. Local officials believe the latest case will not hamper talks on reopening the border with the mainland. But their counterparts will be naturally concerned about any health risks arising from quarantine-free travel, especially when mishandling of the pandemic has led to cadres being removed from office. Although both sides have adopted a so-called zero infection strategy, gaps in its implementation are the sticking point. The foreign business community here may be upset at quarantine rules and other preventive measures, but they still fall short of those across the border. Chief Executive Carrie Lam Cheng Yuet-ngor has admitted the city cannot meet all requirements , such as locking down residents for prolonged periods as they do on the mainland, but has pledged to do everything possible to convince Beijing. The two airport-related cases have, thankfully, not resulted in more infections. But for a country that adopts a zero tolerance approach, one case is too many. From preventing wider outbreaks from imported cases to enhancing contact tracing for travellers, more assurances are needed.