Beijing’s record for handling the Covid-19 pandemic is the envy of most governments. Its detection and prevention methods have ensured the world’s most populous nation has been largely infection-free. Hong Kong having had its own system for determining risk across the border was therefore baffling, particularly as authorities lacked access to the necessary information to be able to accurately make assessments. Their adoption of the National Health Commission’s alert list makes sense, especially as standardisation will be useful for the eventual resumption of normal travel. The differences of determining risk levels went largely unnoticed due to the absence of cases in Guangdong province, where most Hongkongers on the mainland live and work. That enabled a relaxation of rules allowing the city’s residents to return under a quota scheme without having to undergo compulsory quarantine. But that changed on Saturday with the mainland’s announcement of an infection in a district of Guangzhou; under the rules that then applied, the assessment for all of Guangdong was changed from low to medium. Hongkongers planning to come back from the province suddenly faced 14 days of isolation. Those affected were understandably mystified how travel plans in a province bigger in population and area than many European countries could be impacted by a single coronavirus case. Mainland authorities had only increased the risk level to medium in the district involved, not even the city, let alone all of Guangdong. Amid an outcry, the Hong Kong government reversed its decision within the day and announced adoption of the national assessment system. Hong Kong can now be guided by a more timely, accurate and common sense approach. As of Tuesday, the affected Guangzhou district was the only part of Guangdong with a medium level of risk. Other parts of the mainland similarly categorised are four districts of Liaoning province and three in Anhui, where cases have also been confirmed. U-turn for Hongkongers returning from mainland China ‘not forced by outsiders’ Previously, Hong Kong had required citizens coming back from anywhere in the latter two provinces to be compulsorily quarantined on arrival. The standardised approach is more transparent, has science as its basis and puts the two sides in sync. Standardising cross-border risk assessments does not compromise the “one country, two systems” principle. Chief Executive Carrie Lam Cheng Yuet-ngor correctly made the point on Tuesday that it was not fair to quarantine all arrivals from Guangdong when only a single district was affected. The various government departments involved need to reflect on the confusion caused and learn the lesson. There is every need to better understand the mainland’s effective and sophisticated system of prevention.