Singapore is experiencing its worst spate of Covid-19 community infections in close to a year, in a painful reminder of how the virus situation can flare up without warning.
But if contact tracing, testing, and quarantine protocols are as effective as before, and people do not let their guard down, the current situation could be brought under control within the next week or so, experts said.
The Tan Tock Seng Hospital (TTSH) cluster - now numbering 27 - is the nation's first hospital cluster, and comprises staff and patients. One patient, an 88-year-old woman, has died.
The recent cases show that nobody can relax, not even for a moment, stressed Professor Teo Yik Ying, dean of the National University of Singapore's Saw Swee Hock School of Public Health.
"We have seen time and again how countries have had to ramp up restrictions, or even reimpose another lockdown, after they have opened up, and this scenario could become a reality if we become complacent," he warned.
"I certainly hope this is just a blip in our management of Covid-19, and it won't progress on to much further community spread."
The TTSH cluster - the largest of nine open clusters currently - and the cluster which surfaced at Changi Airport Terminal 1, which numbers eight people so far, show that the original index cases had gone on to seed secondary and possibly tertiary transmissions, Prof Teo pointed out.
Nonetheless, the clusters could peter out soon if all steps are followed assiduously.
"If our contact tracing, testing and quarantine protocols are as effective as before, we should see the current blip come under control within the next couple of weeks or so," Prof Teo predicted.
Singapore has already moved to contain the spread of the virus, acting swiftly to ring-fence the cases, testing aggressively, and even enforcing lockdowns in four TTSH wards, for instance.
Prof Teo said: "What's critical is cooperation from the public: If you are requested to go for a swab test, please go for it. If you are given a leave of absence, please stick to it.
"And everyone must continue with personal safe management measures such as mask wearing and social distancing."
The numbers, while alarming, are not large enough to be called a new wave of community infections, noted Associate Professor Alex Cook, vice-dean of research at the Saw Swee Hock School of Public Health.
The number of community cases now is nowhere near the peak in early April last year, when more than 40 new locally transmitted infections were reported daily, he said.
"Everyone has been quite relaxed with the rules lately, and this will be a good reality check for us.
"It is also a reminder to those who have been putting off their vaccinations to get vaccinated, as we cannot expect the community to remain virus-free forever.
"I wouldn't belittle the clusters we're seeing this week - they are a problem we need to get on top of - but they are not currently anywhere near the problem we faced down in 2020," Prof Cook said, although he also noted that not all infections would be detected.
Prof Teo added that the extent of the spread will become clearer only in the next few days as cases are detected.
But there is a good chance that the authorities will be able to break the chains of transmission, given the country's robust contact tracing, quarantine and testing capabilities, which have been built up over more than a year, he said.
Singapore is in a better place than it was a year ago, with more than one-fifth of the population vaccinated, better capabilities in testing, a high take-up rate of the TraceTogether app, and medical facilities reinforced to cope with some degree of surge.
Prof Teo said: "While I expect there to be more community cases that will emerge that are linked to the active clusters, the protocols that have worked should once again help to stop transmission."
The authorities have taken swift action to ring-fence current and potential clusters.
For instance, following an Edgefield Secondary School student testing positive for the virus last Friday, the school will move to home-based learning from tomorrow till Friday, and precautionary measures such as thorough cleaning and disinfecting of the school premises have been stepped up.
At TTSH, all 1,100 inpatients and 4,500 staff working in the wards have been tested as part of a mass screening exercise. The four wards involved in the spread are in lockdown.
Professor Dale Fisher, an infectious diseases expert at the National University Hospital, said the new spike in cases is a test for Singapore, to gauge how it is managing the pandemic.
"We need to think less in terms of waves, but more in terms of clusters and if we can manage these clusters," he added.
This is because these local cases are not sweeping through the community, and the approach is about controlling the spread from these clusters and breaking transmission chains, Prof Fisher explained.
Singapore will have to see if it can shut down the clusters with minimal impact on the rest of society and without resorting to blunt tools like a nationwide lockdown, he said.
"But if there are too many cases and uncontrolled spread, that is when significantly tighter social restrictions will have to come in."
During the May Day Rally on Saturday, Prime Minister Lee Hsien Loong highlighted the need to tighten measures to stamp out the clusters and avoid going into another circuit breaker.
"If we have to do another lockdown like last year's circuit breaker, it would be a major setback for our people and for our economic recovery. Let's not make it happen," PM Lee said in his televised address.
While the nation has honed its defences against the virus, the invisible foe is also becoming more wily.
The pandemic has morphed into a different creature compared with last year, with new strains of the virus adding a layer of complexity in Singapore's fight. These strains could prove to be more transmissible, harder to detect, and better able to evade the body's immune system.
These variants include Britain's B117 strain, the Brazilian P1 variant, South Africa's B1351 and India's "double-mutant" variant, B1617.
Cases of reinfections and infections after people have been vaccinated have also surfaced in Singapore and abroad.
Though vaccines have been largely effective against these variants, no vaccine is 100 per cent effective and breakthrough cases remain. More studies need to be done to determine the risk of infection after vaccination and how long vaccine antibodies remain in the immune system, say scientists.
Prof Teo pointed out: "We need to understand whether the current community clusters are due to the variants, or if they are due to people becoming complacent when socialising and dining together.
"The situation can deteriorate very rapidly if we let our guard down. We need to keep to the spirit of the rules, which have proven to work, to get through this."