Lockdowns appear to be the preferred way to deal with the coronavirus outbreak globally, but they need to be timed well and complement other strategies, experts say.
China has sharply checked its coronavirus infections - reporting just 39 new cases on Tuesday - after locking down Hubei province, the pandemic's original epicentre.
"But the cases have not peaked in China and there is nothing to stop another wave of outbreak being as bad as the first phase," said Associate Professor Alex Cook, NUS Saw Swee Hock School of Public Health's vice-dean of research. Cases peak when half the country has been infected or immunised, halving the rate of transmission.
Yesterday, a lockdown began in Malaysia that will last until the end of the month. In Europe, the pandemic's current epicentre, Italy, Belgium and Paris have also locked down in a bid to curb the spread.
National Development Minister Lawrence Wong, who co-chairs the multi-ministry Covid-19 task force, said a lockdown in Singapore remains an option, but it will not be in place yet.
Prof Cook, the school's domain leader for biostatistics and modelling, said stringent measures must be timed for best effect because they put stress on people and the economy. But they can give countries much-needed breathers. Timing is important "as once the measures are relaxed, the epidemic happens again, but is delayed", he said.
Professor Teo Yik Ying, the school's dean, said lockdowns serve two purposes. "They prevent further importations, especially as Covid-19 is now spreading in many countries and it becomes a real challenge to enforce travel advisories or bans that are specific to individual countries," he said.
"And it is socially responsible to prevent exporting to other countries, and to contain any further spread to within the country."
But a lockdown cannot be a country's only strategy, he said. It must co-exist with other measures like active contact tracing and mandatory social distancing. "Judiciously applying a lockdown as well as timing it carefully can indeed be effective," said Prof Teo, citing China's success.
Prof Cook said a two-week lockdown is not enough as the spread will start again after the shutdown ends. This is because people can still pass the virus to family members and others, who may get sick after the lockdown is lifted - and start the spread all over again.
If such measures flatten the curve by reducing the number of new infections, that would be good, he said.
Both experts agree it is critical to keep numbers below the threshold at which a country will run out of intensive care unit (ICU) beds - as more than one in 10 Covid-19 patients require ventilators to help them breathe.
Prof Cook said in theory, a good approach is to let the number of infections "grow at a rate that is still comfortable, when you still have ICU beds. When it gets near full, implement measures to bring it down". He quickly added: "But I would be anxious about trying to game an epidemic. It may not work out that way in reality."
Until a vaccine is available, even if countries succeed in keeping infections low, there is the risk of imported cases starting another major outbreak. The real worry, said Prof Cook, is less developed countries with poorer healthcare systems where infections could spike, reviving the spread elsewhere.
He said a socially responsible population, where people who are sick self-isolate, can do a lot to reduce transmission. "That will have a big impact on the infection rate."