Covid-19: The Second Wave In Singapore
Singapore’s battle against the novel coronavirus entered a new phase around March 10, when the number of imported cases began to spike sharply. The city-state’s experience could be a canary in the coal mine for other countries still grappling with the first phase of the outbreak.
Some two months after reporting its first confirmed Covid-19 case on January 23, Singapore is well into a new phase of the outbreak, one that is characterized by a bigger wave of imported cases from a larger number of countries.
This second wave began around March 10, according to a breakdown of the Singapore health ministry’s daily Covid-19 announcements. And just like in the first phase, between January 23 and March 09, the worry is that the growing number of imported cases will trigger an even bigger spike in local transmission of Covid-19.
To that end, the authorities in Singapore have rolled out a raft of tough new measures to enforce social distancing, curtail crowds and ring fence “returnees” from Covid-19 hotspots like the United Kingdom and the United States. The Government has hinted that it is prepared to introduce even tougher measures if needed.
This post will take a closer look at how the first and second wave of the Covid-19 outbreak in Singapore differ.
1. DATA AND CAVEATS
This post covers 732 confirmed cases (415 imported, 317 local) announced by the Singapore authorities between January 23 and March 27. Data for the charts were compiled from daily Covid-19 updates on the health ministry’s website. You can download the dataset here, or via my Github repo.
The ministry’s daily updates include Covid-19 cases confirmed on the day of the announcement, as well as those who tested positive a day earlier. For example, the press release dated March 27 would have patients who tested positive on both March 27 and March 26.
To avoid confusion, the charts in this post will only take reference from the dates for official confirmation of infection. These confirmation dates are medical records which will be more reliable and consistent going forward, compared to announcement dates which are more administrative in nature.
Do note, however, that media reports in Singapore are based on new Covid-19 figures announced by the Government on a daily basis. There will be discrepancies if you compare the numbers reported in those articles with those highlighted in the charts here, as they take reference from different dates.
Finally, a disclaimer: This is not a medical study, and I’m not an epidemiologist. It is an attempt to better understand the underlying trends in publicly available information. Extra care has been taken to avoid over-interpreting the incomplete Covid-19 data.
2. MARCH 10: A NEW PHASE BEGINS
There is obviously a lag between the onset of new infections and the authorities’ ability to detect and confirm them. But based on a breakdown of available data, it would appear that Singapore’s Covid-19 outbreak entered a new phase on or around March 10.
That was when the number of imported cases began overtaking the locally transmitted ones — slowly at first, followed by a dramatic surge as seen in the chart below.
Prior to March 10, the vast majority of imported cases involved travellers from mainland China or Singaporeans evacuated from Wuhan, the central Chinese city where the Covid-19 pandemic began.
The first imported case that did not have a China connection— Patient 113 — was confirmed only on March 04, almost six weeks after Singapore reported its first Covid-19 case on January 23.
Patient 113, a 42-year-old French national who had travelled to France, Portugal, Turkey, and the UK, was a sign of things to come even as local cases continued to surpass imported ones for another six days.
On March 10, the number of imported cases took a slight lead over local cases (four imported cases versus three local ones) for the first time in weeks. A week later on March 17, the number of imported cases spiked to 31. And a week after this on March 24, 47 imported cases were confirmed, the highest one-day record for such cases so far.
The imported Covid-19 cases in this second wave were mostly from the UK and the US, in sharp contrast with the China-linked imported cases in the first phase of the outbreak. A more detailed breakdown of the changes in imported cases can be found in Section 4.
There has been a corresponding increase in the number of locally transmitted cases as well in the second phase of the outbreak. Locally transmitted cases in fact hit a current record high of 31 positive tests on March 24, the same day that confirmation of new imported cases also hit a record high.
So far, the authorities have not disclosed any direct connections between the imported and local cases in Phase 2. But we have already seen from several clusters in Phase 1 that this is a distinct possibility.
3. Import-Local Domino Effect
The most notable example of how imported Covid-19 cases can have a “domino effect” on local transmission is the one that involves an infected Wuhan couple, identified as Patients 8 and 9. They arrived in Singapore on January 19 and visited The Life Church and Missions in Paya Lebar that same day.
The Chinese couple infected six church-goers, who then went on to infect about two dozen others in two other clusters (see network chart above). The two Chinese nationals tested positive for Covid-19 only on January 28 and 29. The Singaporeans infected by them tested positive for Covid-19 from February 6 onwards.
The considerable time gap between first contact with an infected person and confirmation of a new infection is worrying given the highly infectious nature of the virus. Though the authorities now have faster test kits and more experience dealing with Covid-19, full contact tracing and caring for patients in high-risk groups remain a highly challenging task.
Case in point: Patient 90, the first Singaporean to die from Covid-19. The 75-year-old woman, who had a history of chronic heart disease and hypertension, began reporting onset of symptoms on February 9. But she only tested positive for Covid-19 on February 23. She died on March 21 after 26 days in intensive care.
With a vaccine still months, if not years, away, the most obvious counter-measure against Covid-19's domino-effect would be for people to reduce social interactions in order to minimize any potential chains of transmission. For Singaporeans who haven’t been travelling, this means taking social distancing seriously and avoiding crowds. For those who just returned recently from overseas, it means strict compliance with the self-quarantine orders.
Singapore’s ability to rein in new infections in this new phase, or to “flatten the curve” as it is popularly known these days, would depend to a large extent on how well residents here comply with these new rules.
4. THE CHANGING PROFILE OF IMPORTED COVID-19 CASES IN SINGAPORE
At the time of writing, Singapore’s 415 imported Covid-19 cases have travel histories involving 45 different destinations. However, the information released by the health ministry in this area has not been consistent, with the travel histories of some imported cases published as “Asean”, “Europe” and “Eastern Europe” without elaboration. The ministry also flagged the travel histories of 19 imported cases as “Pending” without explaining why the information was not available.
If we exclude these four problematic categories, the 41 countries where the imported Covid-19 cases have travelled to (or from) are: UK, US, Indonesia, China, Philippines, Malaysia, France, Thailand, Spain, Italy, Slovenia, Monaco, Taiwan, Ireland, Turkey, United Arab Emirates, Canada, Australia, Bosnia, Norway, Japan, Russia, Iceland, Serbia, Hungary, Denmark, Switzerland, Pakistan, India, Holland, Sri Lanka, Austria, Belgium, Croatia, Mexico, Czech Republic, Portugal, Netherlands, South Africa, Germany, and Sweden.
At least 60 imported cases had travelled to two or more of the countries listed above. The vast majority of imported Covid-19 cases in Singapore had a single source of origin, with the UK leading the current tally:
If we include imported cases with multiple travel destinations before arriving in Singapore, then the number of cases with a UK connection go up to 155. For these cases, the health ministry’s press releases did not spell out where the patients potentially got infected.
The geographic breakdown of the imported cases is even more striking when we split them according to the two phases of the outbreak that we’ve seen so far: the First Wave from January 23 to March 09, and the Second Wave from March 10 onwards:
China, which dominated the number of imported cases in the first phase, is naturally missing from the chart in the Second Wave due to tough travel restrictions that the Singapore authorities introduced in late January against Chinese travellers and those with a recent travel history to the mainland.
The surge in imported cases from the UK and the US appears to be mostly due to Singaporeans, particularly students, returning home in response to the poor handling of the Covid-19 outbreak in their host countries.
A breakdown of the 155 imported cases with a UK travel history showed that:
- 113, or 73%, are Singaporeans, while 14 are Singapore permanent residents.
- About half, or 78, are aged between 18 and 25.
The authorities expect more of these Singaporean students and residents in the UK and US to return in the coming weeks, and are taking no chances. Adapting lessons learnt from the first phase of the outbreak, Singapore has mandated that residents returning from these two countries will go straight from the airport to hotels to serve out a two-week quarantine.
5. GROWING NUMBER OF LOCAL CLUSTERS
The most interesting way to examine the local cases would be to see how the clusters are connected, via network charts. I’ll leave this for a separate post, given the amount of work involved in mapping out the clusters.
Here’s a quick version I rustled up via Flourish’s excellent survey template. You can access it here.
The biggest local cluster so far is the SAFRA Jurong cluster, involving 47 confirmed cases who are connected in various ways to a dinner function on February 15. Many participants at the function had common social circles and took part in joint activities that likely worsened the spread of the virus.
The chart below is useful for getting a better sense of how the spikes in local transmission track the emergence of these clusters:
The spike in local cases from March 24 onwards is due to the emergence of at least three new clusters around the same time:
- The PCF Fengshan cluster (26 cases and counting); the first case emerged on March 23.
- The Dover Court International School cluster (at least 8 cases); the first case emerged on March 24
- The SingPost Centre cluster (at least 5 cases); the first case emerged on March 24
There’s typically a lag of a few days between the first case of a new cluster, and a subsequent spike in overall local cases. Singapore’s contact tracing regime is already pretty aggressive by global standards.
But the goal here would be to further reduce the amount of time needed to establish a new confirmed case’s recent activity history, so that his or her close contacts can be quickly tested and ring fenced from others in their social orbit. I’ll come around to a more detailed look at the local clusters in a future post.
6. COMPARING KEY DEMOGRAPHIC METRICS OF COVID-19 CASES IN THE FIRST AND SECOND WAVE
The outbreak is still evolving rapidly, so there’s not much point in making too many detailed charts at this point. Again, I loaded up a separate survey template on Flourish for those who might want to explore the First Wave Vs Second Wave demographic data in detail. You’ll find it here.
I’ll just focus on a few key areas that caught my attention.
6.1 CHANGES IN LOCAL-IMPORTED CASES MIX
We’ve already seen from the earlier chart that there was a dramatic spike in the number of imported cases in Singapore during the Second Wave. It’s even more striking when the overall numbers are put side-by-side:
Phase Category Total Confirmed Cases
First Wave Local 131
Imported 32Second Wave Imported 383
Local 186
There’s been a more than 10-fold increase in imported cases from March 10 onwards.
6.2 GENDER MIX
We continue to see more men testing positive for Covid-19 than women.
Phase Gender Total Confirmed Cases
First Wave M 92
F 71Second Wave M 328
F 241
6.3 CHANGES IN AGE-RANGE
There’s a noticeable spike of younger Covid-19 patients in the Second Wave, as seen in the 179 cases in the 20–29 age group. This is likely due to the high number of returning students from the UK and US.
Phase Age Range Total Confirmed Cases
First Wave Ages 50-59 38
Ages 30-39 35
Ages 60-69 29
Ages 40-49 28
Ages 20-29 17
Ages 70-79 10
Ages 0-9 4
Ages 10-19 2Second Wave Ages 20-29 179
Ages 30-39 101
Ages 50-59 86
Ages 40-49 82
Ages 60-69 64
Ages 10-19 23
Ages 70-79 22
Ages 0-9 6
Ages 80-89 6
More detailed breakdowns are available in my notebook for this post. I’ll avoid going too far down the rabbit hole at this point.
CONCLUSION
The notable differences between the first and second wave of the Covid-19 outbreak highlight the complexity of trying to contain a pandemic in a globalized era.
In the first phase, Singapore reacted fast and contained the problem relatively quickly while the outbreak was still largely a China-centric affair.
The second phase will be tougher to manage given that the outbreak has now hit almost all corners of the globe. How other governments respond to Covid-19 cases in their own backyard will have a direct bearing on Singapore, as we have seen in the surge of returnees from the UK and US.
For the foreseeable future, Singapore will have to keep an eye out for multiple potential sources of new imported cases, while working to keep local transmission in check.
Containing the outbreak will also present increasingly complex domestic policy challenges. In the first phase of the outbreak, between January 23 to March 09, there were only 8 Singaporeans among the imported cases.
In the second phase, from March 10 onwards, Singaporeans accounted for at least 239 imported cases, accounting for the vast majority in this category:
Phase Category Nationality Total Confirmed Cases
First Wave Imported China 17
Singapore 8
Indonesia 2
Singapore PR 2
France 1
Italy 1
UK 1Second Wave Imported Singapore 239
Singapore PR 34
UK 16
Indonesia 15
Australia 10
Malaysia 9
Philippines 9
No doubt the spike in Singaporeans among the imported cases in the Second Wave involved returning students or worried families who had few options, but the number hints at the broader challenge ahead for the Singapore authorities in convincing its own citizens not to travel abroad, so as not to bring the disease back.
The message might stick for a while, but for how long can Singapore, or other countries for that matter, keep their drawbridges up against a third or even fourth wave of Covid-19 outbreaks? Three months? Six months? A year?
There’s just no telling at this point.
The notebook and data for the charts in this post are in my Github repo. Let me know if you spot errors or do something interesting with this small dataset from Singapore. Ping me at:
Twitter: Chua Chin Hon
LinkedIn: www.linkedin.com/in/chuachinhon
My other posts on the Covid-19 outbreak in Singapore:
* Covid-19: Visual Notes From Singapore’s First 100 Fully Recovered Patients
* Behind The Panic Buying: A Mysterious ‘Leak’ And A Surge On FB As S’pore Raised Its Virus Alert Level
* Going Viral: How FB Reactions In Singapore Surged As Wuhan Coronavirus Outbreak Worsened
Note from the editors: Towards Data Science is a Medium publication primarily based on the study of data science and machine learning. We are not health professionals or epidemiologists, and the opinions of this article should not be interpreted as professional advice. To learn more about the coronavirus pandemic, you can click here.
