Viruses are unpredictable, particularly one as uncertain as that which causes Covid-19. Hong Kong authorities have been right to extend social-distancing rules until at least January 20 and restrictions on face-to-face school lessons despite infection numbers in the fourth wave of the epidemic having substantially fallen. Relaxation should only occur when the disease is under control and that is still far from the case. Worrying new variants, untraceable sources and the impact of festive season celebrations still to be reflected in daily totals prove the point. Schools will be given more leeway to hold in-person classes, although online lessons will remain the main form of teaching until at least after Lunar New Year. Social-distancing and anti-epidemic measures are the tightest yet and will continue to have a heavy impact on businesses such as restaurants, bars, entertainment venues, fitness centres and beauty parlours. But with the risk of a rebound in cases high, a tight lid has to be kept on circumstances. Social-distancing fatigue has to be of particular concern. Crowds returned to streets and shops during recent holidays. Although rules dictate only two people can be together in public places, there is no control over private gatherings. In coming days and weeks, the city will find out from infection figures whether warnings about the need to limit the size of winter solstice, Christmas and new year celebrations were followed or ignored. A fresh cluster at one of Hong Kong’s biggest infrastructure projects , the Tseung Kwan O-Lam Tin tunnel, also raises questions about adherence to rules. All 1,500 workers have to undergo mandatory testing after 12 were infected. The site had only been reopened for a few days after suspension from December 9 to 27 following a 28-person outbreak involving bar benders and their close contacts. Lessons need to be learned if Hong Kong is to bring Covid-19 under control and attain the goal of zero infections. ‘Explosive outbreak’, endless rules, vaccines: Hong Kong’s top 20 Covid-19 headlines Vaccines are gradually being rolled out and Hong Kong is expected to receive its first batches this month. It could be a year or more before enough doses have been produced and the 70 to 80 per cent of populations in countries are vaccinated to bring about herd immunity. But highly virulent new strains from Britain and South Africa are already making their way around the world and have been detected in the region, and scientists are unsure whether the variants may undermine the effectiveness of immunisation. Keeping tight control of borders is important; Japan, South Korea and Britain have in recent days recorded all-time high numbers of infections. Relaxation of rules can only occur if all in society exercise restraint, avoid gatherings between households, wear masks in public, maintain the highest standards of hygiene and strictly observe government measures.