HONG KONG (BLOOMBERG) - As the world struggles with the rapid spread of Covid-19, Hong Kong appears to be having success controlling it - in part because the memory of a similar virus in 2003 prompted a public outcry early on.

Hong Kong's government quickly implemented restrictive "social distancing" measures now being hotly debated around the world, in part because of pressure from medical workers to close its border with China at the beginning of the outbreak.

Those included closing schools, cancelling large-scale events, shutting government offices and ordering civil servants to work from home - a move that many companies quickly followed.

Hong Kong's experience with Severe Acute Respiratory Syndrome - which killed almost 300 people of more than 1,700 infected, the most outside of mainland China - impacted the psychology of the city, said Dr Nicholas Thomas, an associate professor at the City University of Hong Kong.

Many residents wore surgical masks and avoided gatherings from the very start of the outbreak, a practice that continues more than six weeks later.

"As soon as the virus started to break out, and people read 'China' and 'coronavirus', people remembered," said Dr Thomas, who has edited an academic book series titled Health Security and Governance.

"The social part is one of the reasons why we've been able to keep the virus cases so low, because in some way the public has been able to make the government take measures."

On Tuesday (March 17), the government said it was extending mandatory 14-day quarantines for all visitors arriving from outside of Greater China, reiterated that city residents should avoid travelling, and said it would keep some schools shut beyond an original April 20 deadline.

'We will be very careful on school resumption," Hong Kong Chief Executive Carrie Lam said.

"From what we see now, a complete school resumption on April 20th is quite impossible. And even if the situation has stabilised, we could only reopen schools in phases."

EARLY MEASURES

In recent days, the virus's spread in the US - highlighted by the National Basketball Association's decision to suspend the season - has driven home the need to avoid large gatherings, even as some government officials have maintained there's no reason to panic.

Recent high-profile infections, including actor Tom Hanks, the Australian home affairs minister and the wife of Canadian Prime Minister Justin Trudeau, also underscore the need to take early precautions.

Most of Hong Kong's restrictions were put in place at the end of January, when the city had only a handful of cases.

As of Monday, it had 157 cases in total, including returnees from the stricken Diamond Princess cruise ship, and only four deaths.

By contrast, South Korea didn't start taking unprecedented measures until Feb 23, when hundreds had already been infected. It has now seen more than 8,100 people infected and 75 deaths.

New York City also acted much later by comparison. On Sunday evening, Mayor Bill de Blasio announced that public schools would be shut from March 16 as the city's tally soared over the weekend to 463 confirmed cases and five deaths.

For Hong Kong, the relative success marks a bit of good news in what has been a devastating 12 months for the economy.

The virus is further curbing growth after violent pro-democracy protests periodically shut down large parts of the city in the second half of 2019, prompting Beijing-appointed leader Lam's popularity to plummet.

The effective virus response hasn't helped Ms Lam much. She initially resisted public pressure to fully shut the border with China, relenting only as thousands of medical workers began a strike that put pressure on officials and the health system.

Her approval rating rose to 13 per cent on March 3 from just 9 per cent on Feb 27, according to the latest survey released by the Hong Kong Public Opinion Programme.

EARLIER INTERVENTION

Deploying measures early can have a dramatic effect. Research on the 1918 influenza pandemic in the US showed cities that had implemented multiple "non-pharmaceutical interventions", including closing schools and churches, experienced death rates that were as much as 50 per cent lower - as well as less severe outbreaks - than those that did not.

Medical researchers estimated China could've reduced the number of confirmed Covid-19 cases by as much as 95 per cent if officials had implemented non-pharmaceutical interventions - from containment and isolation to social distancing - just three weeks earlier than they did.

Even implementing them one week earlier would have reduced China's cases by 66 per cent, while the number could've jumped 18 times if such measures came three weeks later, according to the study this month funded in part by the Bill & Melinda Gates Foundation.

Social distancing measures can be a critical part of stopping the virus after governments have already implemented other containment measures, said Dr Benjamin Cowling, a professor and co-director of the World Health Organisation Collaborating Centre for Infectious Disease Epidemiology and Control at Hong Kong University's School of Public Health.

Governments need to conduct tests to identify and quarantine infected people and those with whom they've had contact, while also reducing imported cases from overseas, Dr Cowling said.

Once an outbreak has occurred and it becomes more difficult to track down suspected cases, social distancing measures like closing schools, working from home and voluntarily avoiding crowded areas is key, he said.

"Social distancing becomes more important if there's sustained transmission in the community and we want to slow it down, because at that point, the first two measures won't be as effective," he said.

"And hopefully the US and Europe and other countries can learn from Hong Kong and Singapore in how social distancing can be applied and how our populations can be aware."

Singapore - which did not close schools or offices - initially saw success containing the virus, but has more recently seen a second wave of cases that brought its total to 226.

Recent cases seem to have mostly been imported from abroad, rather than through local transmission.

Taiwan, which has carefully screened flights from China and has ordered strict fines for quarantine breakers as high as US$33,228 (S$47,175.62), has also seen success - with just 59 cases and one death.

Hong Kong is now also worried about a second wave of cases. A local newspaper lambasted expats gathering in bars without masks - showing that social pressure for social distancing continues in spite of government measures.

"There is a strong responsibility of people to adhere to social norms and respect the wider community," said Dr Thomas from City University.

"There's been an awareness in the last two decades that these problems are there and that we have to do something about it."