Prof Leo Yee Sin: The pandemic expert helping us beat the virus with research and data

by Sophie Hong  /   December 3, 2020

As executive director of NCID, Prof Leo Yee Sin provides clinical leadership by understanding the virus and advising on the appropriate actions.


In the past 10 months, Professor Leo Yee Sin, executive director of the National Centre for Infectious Diseases (NCID) had been working 12 to 14-hour days. And like the rest of us, she’s looking forward to travel again.

“Everyone is yearning for a holiday, right? Me too,” she says with a small chuckle. That holiday would be a well-deserved break for Prof Leo. After all, in this long-drawn battle against Covid-19, many of us had turned to her for her expertise in infectious diseases.

“People look towards us to provide information,” the head of NCID acknowledges. “But when the information is scanty or non-existent, it can be a challenge. We just have to make the best guess and judgement, and at the same time, utilise our resources to gather more information and give us clarity,”

“To make a decision right at the beginning, when you have little to no information, is not an easy thing to do,” she adds.

Our national response to Covid-19 cannot be attributed to the efforts of one person alone. After all, it boils down to everyone playing their part, right down to the general population’s compliance with safety measures, such as social distancing and masking up.

But at the heart of this coordinated effort against the invisible enemy stands Prof Leo, steadfastly anchoring our pandemic response with her clinical leadership.

Studying the new pathogen

The NCID is a facility that serves as a one-stop-shop for infectious disease management and prevention. The 14-storey building, situated opposite Tan Tock Seng Hospital (TTSH), houses 17 wards with 330 beds, a clinic, laboratories, and research facilities. This enables Prof Leo and her multi-disciplinary team of doctors, nurses, epidemiologists, researchers and medical technologists to capture and analyse data on emerging infectious diseases more efficiently.

People look towards us to provide information.

Prof Leo Yee Sin

When asked about the first few months of the outbreak, the words “very stressful” tumbles out of Prof Leo. It’s not hard to understand why – it was an unprecedented public health crisis, and infectious disease experts around the globe were racing against time to unearth more information about this new virus. How was it transmitted? What was the infectious period? Why did some people develop a more severe illness?

For these answers, Prof Leo turned to her multi-disciplinary team at NCID. As the facility was designed to contain and manage infectious diseases, they were able to analyse their own operational data set and arrive at conclusions swiftly. That, and working with the World Health Organization and other infectious disease experts, both locally and internationally, to exchange information.

She recalls having to be in conferences almost every night during the first few months of the outbreak. And because Geneva is seven hours behind Singapore, that stretched her workdays into 14-hour-long affairs. She jokes that a small mercy was that she could switch her camera off during these Zoom sessions, allowing her to sit in and have dinner at the same time.
“There was not a lot of rest during that period, but it was fine because it meant that we were able to gain new knowledge and answers that enabled us to move faster than the virus,” she says. And while the schedule, in hindsight, was punishing, she didn’t mind.

“You just have to work and get things done,” she says matter-of-factly.

Ready before first imported case

Leo Yee Sin_National Centre For Infectious Diseases_Woman Of The Year_incopy

One of the key lessons Prof Leo learnt early on as an infectious disease expert: There is little margin for error in her role. More than two decades ago, when she was a consultant, she was tasked with coordinating a response to Nipah virus – an emerging infectious disease at that time, a first for her.

When a busload of close to 50 suspected patients showed up at the clinic to be screened, the team got down to work. It was only after they were done and dusted for the day that a frightening thought crossed her mind: what if the virus could transmit from human to human?

“We were so fortunate because that virus didn’t have human-to-human transmission properties,” says Prof Leo. “That kind of mistake shouldn’t happen again.” That stuck with her, and is the reason why segregation is a routine precaution that she takes in all her responses to emerging outbreaks.

Fast forward to 2020. When Prof Leo learnt that human-to-human transmission is possible with Covid-19, she knew that there would be community spread, and that detection would be crucial in containing it. Before we even had our first imported case, the National Public Health Laboratory at NCID had already started work on detection methods based on the genetic sequence published by China.

“We were ready when the first imported case came in,” she recounts. With this level of efficiency, it’s easy to forget that NCID had only officially been open for a few months when the outbreak first hit our shores back in January.

“She takes on challenges in unchartered territories and charges on faithfully even in the face of obstacles,” says Dr Margaret Soon, director of nursing at NCID.

“She is clear in her mission, and leads with clarity and purpose.”

Mr Albert Tan, NCID’s director of operations, expressed the same admiration, and was particularly struck by something that Prof Leo said.

“She told me that this is a virus that we do not fully understand yet, and that we should never let our guard down,” he lets on.

To understand how Prof Leo provided effective clinical leadership during this time of crisis, one needs to look at her methodical approach.

“A lot of the time, it’s the ability to have some degree of inclination. When you look at the issue, you start to query and form a hypothesis. Then you test your hypothesis. When we went to the ICU, we saw mostly people in their 50s, 60s, and 70s there. We brought that observation back and asked,
does age play a factor in the severity of the disease?”

“Then, you need to plough through the data, and you’ll find your answer that way,” she explains, adding that it was a good thing NCID was able to gather and analyse data on an emerging virus so quickly.

“By the time you realise you can handle it differently, you’re able to have a wider group of healthcare institutions coming in. That is precisely what happened with Covid-19,” says Prof Leo.

At the beginning, NCID received 60 to 70 per cent of the cases. To cope with the demand within campus, they scaled up inpatient beds from 330 to more than 500 beds with assistance and support from TTSH. At the peak of the outbreak, other public, community, and even private hospitals helped with the caseload.

Figuring out a safe exit

By now, we have all experienced two months of tough circuit breaker measures, more than half a year of working from home and, of course, close to a year of social distancing.

Prof Leo understands that as an infectious disease expert, it lies on her shoulders to help people understand why these measures were necessary.

“At the beginning, there’s this lack of definitive, absolute information. People wanted to know if it’s a ‘yes’ or ‘no’, but a lot of the time, it’s not binary,” she says, bringing up the mask mandate as an example.

“The challenge is then, how do we let people understand that this is evolutionary, things are still changing, and we’re still gathering more information,” she adds, acknowledging that the social isolation and disruptions haven’t been easy on people and businesses.

Over the course of our one-hour chat, one gets the sense that there’s still not enough hours in Prof Leo’s days. Her phone chimed numerous times. She arrived for the interview on the dot, and left precisely 60 minutes after.

She lets on that she had taken the day off two days ago and, because of that, she hasn’t been able to catch up on all her e-mails.

It is important for us to remember that this pandemic may not be our last.

Prof Leo Yee Sin

“I hope it’ll be over as soon as possible, but I think we’ll have to be patient because defeating this virus is not an easy feat,” the 61-year-old admits frankly. For one, there have been reported cases of reinfection in several countries, including Hong Kong, the US and India. Prof Leo points out that for reinfections to happen, there must be transmissions in the community – and this is what she and her team are actively looking at.

And even if there’s a vaccine, her work wouldn’t be over just yet.

“It is important for us to remember that this pandemic may not be our last. There will be new pathogens. It is important for us to build a system where we can cope with challenges from a different pathogen or emerging infections,” she emphasises.