This story was first published on Feb 16, 2014.
When it comes to mutant influenza strains, H7N9 is the one to watch.
Although catching it remains a low risk for Singaporeans, the new bug has already appeared in neighbouring Malaysia, and the authorities here are keeping a close eye on what unfolds.
"Our guard is up," said Associate Professor Raymond Lin, head and senior consultant at the National University Hospital's Division of Microbiology.
"We probably won't know how serious it is until winter in China is over, a time when the flu in birds dies down. If there are fewer cases then, it will mean that the virus is still unable to transmit efficiently among humans.
"The H7N9 virus has continued to change since it first affected humans in 2013, and this is cause for concern that it might spread more easily."
H7N9 is a deadly killer. Striking deep into the lungs, it causes severe respiratory illness in most patients, killing one in three.
The new bird flu strain first reared its head in China last year, and infections started coming to light in March.
It has since claimed more than 70 lives.
A Chinese tourist in East Malaysia's Kota Kinabalu - who had arrived from H7N9 hot spot Guangdong - became the first infected person outside China and Taiwan last week.
In addition, more people are getting infected: There were 127 H7N9 cases in China last month, almost as many as all the cases in the country last year.
In Singapore, a top destination for Chinese nationals, H7N9 detection kits are on hand for hospitals here to use if suspected cases turn up.
"Our hospitals remain vigilant to test for H7N9 and other avian influenza where clinically indicated, such as in patients with serious respiratory illness and a compatible travel history," said the Ministry of Health in a statement.
All suspected and confirmed cases will be isolated, and contact tracing will be done if a case is detected.
Nonetheless, the ministry said, "the public health risk to Singapore remains low as the characteristics of H7N9 in human infections have not changed".
Dr Masafumi Inoue, group leader of medical diagnostics at the Agency for Science, Technology and Research's Experimental Therapeutics Centre, said: "Our H7N9 detection kit has been validated and ready for use at a local hospital since last year."
He and his colleagues at research institutes and hospitals are constantly monitoring the virus for genetic changes, he added.
Flu viruses keep vaccine makers playing catch-up because they are so good at mutating.
Earlier this month, scientists in China sounded the alarm after a new bird flu strain, H10N8, killed an elderly woman last December and infected someone else last month. So far, it has affected too few people to be considered a threat.
Viruses like H7N9 are so virulent because they penetrate deep into the lungs and internal organs.
However they are not so good at sticking to the upper respiratory tract of patients, which makes them less infectious when the person coughs or sneezes, for instance.
In addition, because bird flu viruses are so different from human flu viruses, most people have no immunity to them.
"In every infection, some of the virus RNA, its genetic make-up, changes. In many cases, the virus dies off. Sometimes it changes enough so that current vaccines become ineffective," explained Prof Lin.
"But it's relatively rare to hit the jackpot and jump from animals to humans, then spread easily from one person to the next."
Most of the H7N9 infections are believed to be due to exposure to infected poultry or contaminated environments, as the strain has also been found in poultry in China, said the United States Centres for Disease Control and Prevention (CDC).
Laboratories all over the world are working to better understand and guard against the virus, and to produce a vaccine.
Dr Michael Shaw, associate director of laboratory science for the CDC's influenza division, noted that one challenge was that the virus causes vastly different reactions in birds and humans.
"Since this is causing no symptoms in the birds, it's flying under the radar screen, so to speak, which means it might be more widespread than we realise," he said.
The last missing piece before H7N9 becomes a pandemic is for it to be easily passed from person to person.
"It's quite clear that humans are definitely receptive to the virus," added Prof Lin.
"What is not clear is whether infected patients can pass it on to the second and third generation of patients. If the spread is inefficient, the virus could die out."
So while there is little cause for concern here, it pays to be vigilant.
Scientists say that the next flu pandemic is bound to happen.
When that will be and whether H7N9 does manage to "hit the jackpot" is the question.