Covid-19 tests for residents of a Housing Board block in Hougang and another in Pasir Ris are an example of the ring-fencing measures being employed to detect and limit the spread of the coronavirus pandemic in Singapore. The containment strategy was employed earlier at Tan Tock Seng Hospital, which closed a ward where a nurse and then a few patients had been diagnosed with the disease. The hospital enlarged the ring-fence by locking down more wards and stopping the admission of new patients. The quarantining of all close contacts and increased clinical surveillance were other steps taken to contain the geographical ambit of the disease. In schools, ring-fencing has taken the form of the move to home-based learning from May 19 to May 28.

Changi Airport, too, has moved to tighten procedures for staff and passengers with more stringent measures. These include segregating about 14,000 airport workers into three distinct zones, with strict measures to ensure that the 4,400 workers in the highest-risk zone are protected from Covid-19 and isolated from other staff and the public. Travellers from very high-risk countries will also be escorted to remote gates in a terminal, closed for renovation, for immigration clearance and then taken directly to their quarantine facility from the gate by buses. These latest steps are welcome but many here have wondered why such measures could not have been adopted earlier, and perhaps forestall the emergence of the Changi cluster of over 100 people this month. Many of the infected contracted the more infectious B1617 variant that is of concern here and in other countries. While the authorities should be guided by the World Health Organisation's advisories, acting pre-emptively should have also been an option. Changi remains a point of contact with a now-infected world, and it is nevertheless heartening that successive steps have been taken to respond to the threat of any leakage, including the measures announced on Monday.