SINGAPORE - The chief health scientist at the Ministry of Health (MOH) and the man who was responsible for leading Singapore's public health response to the 2003 Sars epidemic has cautioned that the number of coronavirus cases in Singapore can rise anytime.

While the country has managed to slow the spread of the disease, the virus continues to spread rapidly around the world.

Professor Tan Chorh Chuan told The Straits Times: "Singapore's approach of actively looking for new cases and quarantining close contacts has been effective in ring-fencing clusters of infection so far, and we have not seen evidence of community spread... However, it is premature to say that the worst is over.

"Given the rate at which new cases are being reported around the world, there is always a risk of new imported cases. We therefore have to remain vigilant," he added.

The outbreak has evolved rapidly since it originated in Wuhan, China in December. It has spread to more than 40 countries and the total number of cases is now more than 80,000, with the bulk of them in China. On Tuesday (Feb 25), the number of new cases reported outside China exceeded the number of new ones in China for the first time.

There have been 96 confirmed cases here, of which 66 have fully recovered.

World Health Organisation director-general Tedros Adhanom Ghebreyesus told a briefing in Geneva on Wednesday that the sudden increases in cases in Italy, Iran and South Korea were "deeply concerning".

Italy now has more than 400 cases and 12 deaths; Iran has 139 cases and 19 deaths; and South Korea 1,595 cases and 13 deaths. Singapore advises against non-essential travel to Daegu city and Cheongdo county in South Korea in addition to mainland China.

Experts now know that the virus is highly transmissible between people, said Associate Professor Hsu Li Yang, programme leader for infectious diseases at the National University of Singapore's Saw Swee Hock School of Public Health.

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"It spreads between people in a similar fashion as influenza (i.e. primarily droplets and contact) but because it is a novel virus, there is no immunity to it - unlike in the case of seasonal influenza - and hence, it appears to be highly transmissible."

Some scientists have predicted that half or more of the world's population could be infected with Covid-19.

Prof Hsu said this is based on epidemiological modelling projections and will occur only if nothing is done to stop the spread of the virus, as is the case with seasonal flu, for example.

"The outbreak is more serious than initially thought and the worst is yet to come for most countries," he said.

"However, given current active and massive interventions in many countries such as South Korea, Italy, Japan and Singapore, it is unlikely that the world will get to the stage where half of its population is infected with Covid-19," he said.

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The WHO's Dr Tedros said on Wednesday that Covid-19 has pandemic potential, even though China has fewer than 80,000 cases in a population of 1.4 billion people while the rest of the world has 2,790 cases in a population of 6.3 billion.

"The primary objective of all countries with cases must be to contain the virus... At the same time, all countries, whether they have cases or not, must prepare for a potential pandemic," he noted.

"Every country needs to be ready to detect cases early, to isolate patients, trace contacts, provide quality clinical care, prevent hospital outbreaks, and prevent community transmission."