Explaining Circuit Breakers and Masks
Prime Minister Lee Hsien Loong’s address to the nation last Friday marked a new policy direction in Singapore’s fight against COVID-19. Apart from closing most workplaces and schools, the government now wants citizens to stay home as much as possible, and wear masks if needed. “We looked at the situation on a daily basis and we decided that we couldn’t afford to wait any further because there are very worrying trends,” said Minister for National Development Lawrence Wong at a press conference.
But what exactly are these worrying trends? Why has the Singapore government moved to implement harsher measures over the past few days? Why has it reversed its position on wearing masks only if sick? A surface level reading of the situation would attribute it to the rapidly rising number of cases. But this reading glosses over the fact that a majority of new cases over the past few weeks were residents returning from abroad. These cases are digestible as the returnees can be quarantined and isolated — minimising the risk of community spread.
What is truly scary is the number of unlinked local cases, which now make up nearly half of the total local cases announced each day. This suggests that there is a high probability of undetected or hidden cases within the community. A new Singaporean study published in the Centre of Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report gives us insight into why this might be the case.
What does the study say?
In the study, researchers looked at all the confirmed COVID-19 patients from January 23 to March 16 and found 10 presymptomatic transmissions of the virus. In other words, in at least 10 different instances, individuals with the virus infected others without getting symptoms themselves or even knowing that they were sick in the first place. The study then lays out a few case studies that might prove the existence of presymptomatic transmissions.
1. Cluster at Life Church and Missions in Paya Lebar
In the formation of this cluster, two visitors from Wuhan – a woman aged 56 (Patient 8), and her husband also aged 56 (Patient 9) – arrived in Singapore on January 19. They visited the Life Church and Missions in Paya Lebar on the same day and had symptoms show up a few days later on January 23 and January 24 respectively. In visiting the church however, they managed to infect three other people — a man aged 53 years (Patient 31), a woman aged 39 years (Patient 33), and a woman aged 52 years (Patient 38).
It is interesting to note that patient 38 wasn’t even present at the church when the couple from Wuhan visited. When contact tracers reviewed CCTV footage, they realised that she had occupied the same seat in the church that they had, later in the day. This aligns with a study that the New England Journal of Medicine just published proving that the virus can remain stable on different kinds of surfaces within a controlled laboratory setting. They found that it was still detectable on copper for up to 4 hours, on cardboard for up to 24 hours, and on plastic and steel for up to 72 hours.
2. SAFRA Jurong Cluster
On 15 February, members of a Hokkien singing group attended a dinner at the SAFRA Jurong’s Joy Garden Restaurant ballroom. One of the attendees, a 54 year woman (Likely patient 166) caught the virus. Nine days later, on 24 February, the woman took part in singing classes and infected a 63 year old woman (Likely patient 242). At the point of transmission, patient 166 did not have symptoms, and only developed them two days later.
3. Ng Teng Fong General Hospital Nurse and Husband
A 37 year old male Filipino national (Patient 178) traveled to the Philippines on February 23 – March 2. At some point during this trip, the man came into contact with a patient with pneumonia (who later died) and caught the virus. After returning to Singapore, patient 178 likely transmitted the infection to his wife (Patient 167), aged 35 years. Presymptomatic transmission here was likely as both patients only developed symptoms on March 8.
4. Teacher at MY World Preschool and Husband
In another imported case, an American citizen aged 32 (Patient 204), traveled to Japan during February 29–March 8, where he was likely infected. After returning to Singapore, the man presumably passed the virus to his 28 year old Filipino wife, who was a teacher at MY World Preschool. Yet again, presymptomatic transmission was possible as both patients only developed symptoms on March 11.
The main takeaway here is that a lack of symptoms doesn’t mean you can’t infect someone else. Mr. Robert Redfield, the director of the Centres for Disease Control and Prevention (CDC), took this one step further by suggesting that about 25 percent of people infected with the coronavirus don’t present any symptoms at all and are asymptomatic. In other words, according to him, perfectly healthy people might be spreading the virus without knowing — making the virus a more potent threat.
This newfound understanding of the virus has had a few policy implications in Singapore. Firstly, it proves that the government cannot contain the virus by just quarantining sick people. Interactions on a societal level have to be minimised as we don’t know who might be shedding the virus. This might explain the harsher measures announced on Friday — workplaces and schools are major points of interaction and closing them might help reduce cases of presymptomatic and asymptomatic transmission. Secondly, the earlier recommendations of wearing masks only if you’re sick is insufficient due to these very same reasons. Thus, the government has announced that it will no longer discourage people from wearing face masks, and will be distributing reusable masks to each citizen.
The study also reflects the importance of Singapore’s contact tracing measures. The strong surveillance systems that have been put in place to detect cases in Singapore, combined with efforts from authorities to contact trace, has led to a wealth of data for researchers. Studies like the one mentioned in the article would not be possible if countries give up on contact tracing. An understanding of the virus’s behaviour and mechanics is imperative for more informed policy making.
How reliable are these studies?
As with any study, this one has its own limitations. Firstly, although these cases were thoroughly investigated, there is a possibility that unknown sources might have passed on the virus to the patients, instead of the presymptomatic close contacts. The study however notes that this is unlikely “given that there was not widespread community transmission of COVID-19 in Singapore during the period of evaluation” and that there were “strong surveillance systems” in place to detect cases.
Secondly, there might have also been recall bias when contact tracing efforts were underway. Patients might have forgotten when they started having symptoms, especially if they were mild. This might cast doubt on the period of presymptomatic activity.
Lastly, some asymptomatic patients (with no symptoms at all) might have reported irrelevant symptoms, considering that during interviews there might have been an expectation to say that symptoms were present, no matter how mild. As such, an underdetection of asymptomatic patients is likely.
Even with these limitations in mind, the overall picture that the study paints corroborates data and stories that we’ve been hearing from around the world. The virus is being transmitted by unknowing patients, who are either asymptomatic or presymptomatic, and is being transmitted easily.
All of this underscores the need for effective social distancing measures and personal discipline. Act like you are sick, even if you aren’t, and be a little bit more cautious in public places. As the government likes to say, the health of all does indeed depend on each one of us.
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