Authorities have suspended plans to mass-test Hong Kong’s residents for the coronavirus. That is not to say the idea has been abandoned; as Chief Executive Carrie Lam Cheng Yuet-ngor explained, timing is key for any such exercise. But when utilised at the first sign or latter stages of an outbreak, the worth of universal screening is immeasurable, as Shenzhen’s recent week-long lockdown showed. Strict prevention and control measures in the neighbouring metropolis, which has almost twice the city’s population, appears to have ensured the spread of the virus has been contained. An outbreak of the highly transmissible Omicron variant was inevitable given Shenzhen’s proximity to Covid-stricken Hong Kong. Lockdown measures to test, trace and quarantine were implemented on March 13, with public transport suspended and communities and industrial estates placed under closed management. Such stringent steps have been effective in preventing the spread of strains of the deadly disease across the mainland since the start of the pandemic and are a critical weapon in the battle. The fight apparently won for now, much of the city was back to normal on Monday. With speed and clarity, mass testing quickly identifies people with active infection so that close contacts can be found, screened and isolated to interrupt the spread of the disease. Talk by Hong Kong officials of a week-long lockdown, either citywide or of districts, to carry out three rounds of testing, sparked widespread concern. No specific details having been given, and the prospect of being forced to stay at home or severely limited in movement as on the mainland, panicked some people to the point that supermarket shelves were stripped of necessities. The relief that Lam has said the plan will not go ahead for now is palpable. But universal or district-wide testing should not be dismissed. If utilised at the start of the latest wave of the virus at the end of December, the city would perhaps not have endured the pain of the past three months. Hong Kong lacks the mainland’s community organisation network and logistical capacity to make such an effort effective. The virus is an ever-evolving threat and such a step should not be ruled out. Authorities have to prepare for when the need arises.