Reminder to Hong Kong: the Omicron variant of Covid-19 can upset the best-laid plans. For evidence of that we need look no further than Shanghai. In a major U-turn in the pre-dawn hours yesterday, China’s financial hub imposed a lockdown for mass testing on a vast swathe of the city that was decided only late the previous night. This follows repeated assurances by officials that the city need not go into a lockdown to contain the spread of a coronavirus outbreak. Shanghai has locked down its eastern half on the bank of the Huangpu River for four days of mass testing, to be followed by the western bank for three days. This comes as rival Hong Kong prepares to lift draconian restrictions on normal life as daily tallies of infections and deaths gradually decline. It is a lesson to Hong Kong, as it tries to strike a balance between controlling Covid and economic recovery. The international and local finance and business communities have pressured the city’s government with growing intolerance of restrictions and alarm at the prospect of mass testing and even lockdowns. Hong Kong’s standing as an international finance centre was seen to be at stake. The government’s move to ease restrictions, from travel to face-to-face schooling and social distancing, has been widely welcomed. but every precaution must be taken to see that it does not come at the cost of another surge of infections. Otherwise Hong Kong, too, could face a U-turn and even more restrictions. Shanghai lockdowns split China’s financial hub to control Covid-19 risk Until this month, Shanghai, population 25 million, had been held up as a model for others, recording just 400 infections and seven deaths in the two years since the coronavirus emerged, compared with more than 11,000 infections since March 1 as of Sunday. Residents are now being confined to their neighbourhoods and all public transport as well as privately owned vehicles are barred from travelling between the two areas. Companies can still operate either under the “closed loop” isolation system or on a work-from-home basis. The stock market remains open. The huge lockdowns mark a deviation from the so-called Shanghai model of pandemic management, with rolling 48-hour lockdowns and testing of individual neighbourhoods while largely keeping the metropolis running. The more decisive intervention is still not citywide but the current stage involves about 8 million people, more than Hong Kong’s population. Hong Kong does not have the resources to isolate and test on a comparable scale but, as with the Shenzhen lockdown and mass testing earlier this month, there are lessons to be learned in minimising disruption. Paramount is readiness to act quickly and decisively in any eventuality, including a new surge if the spread of infection is to be limited.