The power of mathematical modelling in infectious disease outcomes

“There is nothing quite like hearing about a ship with passengers exhibiting unknown symptoms to focus the attention on infectious disease and the need to investigate potential outcomes,” said Professor Sheetal Silal. She mentioned the recent hantavirus outbreak as an attention-grabbing opening gambit in her inaugural lecture on 12 May.

In an inspiring and engaging speech titled “Models, Policy and People: Predicting Health Impact in a Complex World”, Professor Silal addressed a full lecture theatre and extended online audience, which spanned academics from Cape Town to Oxford, public health officials, postgraduate students, family and loved ones.

Silal, once a bored UCT actuarial science student who crocheted her way through lectures, discovered her life’s passion when she turned her gift for mathematics to public health and real-life outcomes that impact people and communities. It took a pivot thanks to a mentor, the late Emeritus Professor Theo Stewart, into a master’s in operations research, and the fortuitous reading of a paper on modelling malaria outcomes, that led to a PhD in mathematical modelling of infectious diseases.

“Ultimately it is about human safety. Using mathematical modelling and simulation, we can create a virtual reality of a disease within a population, and then experiment on it and interrogate it in a fraction of the time and cost you could do in reality. In this way, you can draw on the experience of a 100-year history in minutes, and help the government plan and respond better.”

Creating actionable insights

Silal focuses on unpacking vast, complex models, systems and data in such a way that it creates actionable insights for public-health decision-makers, some of whom were in the audience. As such, she has played a pivotal role in promoting the use of modelling as a decision-support tool in enabling a broader understanding of the dynamics of infectious diseases, notably malaria, COVID-19 and other infectious and vaccine-preventable diseases such as measles and rubella.

“Sheetal has a rare ability to link mathematical modelling to real-world decision-making,” said Jared Norman, a research officer at UCT’s Modelling and Simulation Hub, Africa (MASHA). “She is a storyteller. She understands that a result nobody understands changes nothing. A result that lands – that reaches the decision-maker, the clinician, the policy maker – changes everything. She has spent her career building that bridge.

“It is not just producing excellent science but making sure it reaches the people who need it most.”

Today Silal is the director of MASHA, a professor in UCT’s Department of Statistical Science, and a leading figure in the field – not only in Africa but globally. She is also an honorary visiting research fellow in Tropical Disease Modelling at the Nuffield Department of Medicine at the University of Oxford.

As the chair of the World Health Organization’s (WHO) Immunization and Vaccines-related Implementation Research Advisory Committee and a member of the WHO Collaboratory Technical Advisory Group, she plays a role in shaping global health strategies and promoting the use of modelling in health policy and planning.

“Professor Silal’s research speaks to some of the most pressing challenges we face – not only in South Africa, but globally,” said Professor Elelwani Ramugondo, UCT’s deputy vice-chancellor for People, Culture and Society in her welcome address. “It’s about people. Behind every data set lies communities and realities faced.”

The Minister of Health on speed dial

In 2020, the MASHA research team was thrown into a baptism of fire with the onset of the COVID-19 pandemic. With the world in crisis and a potentially deadly disease on the doorstep, Silal and team created a bubble in which they worked through lockdown, often putting in 16-hour days. Silal worked 20 hours, playing a pivotal role in harnessing modelling as a decision-support tool for the National Department of Health.

“This kind of modelling calls for tenacity and adaptability,” explained Silal, who was a leader within the South African COVID-19 Modelling Consortium (SACMC), helping guide the government in its pandemic planning and response. Facing unrelenting pressure day after day, they worked with ever-changing data, factoring in fresh evidence while negating newly disproved theories.

“It all comes down to actionable insights for public health decision makers. Do we need vaccines? Will one work? Do we need two?”

In so doing, the SACMC was helping to inform everything from government policy, and the budget needed to fund SA’s response and vaccination programme; to national, provincial and district practicalities such as staff, bed, ventilators, oxygen, drugs, testing and mortuary requirements. They also modelled the macroeconomic impact on the country’s economy and monitored resurgences of COVID-19.

“It was not just about the immediacy of COVID, but what the future held,” Silal noted. “Maths modellers were called ‘witches’. People wanted predictions, but modelling is so much more useful than just that.

“It all comes down to actionable insights for public health decision makers. Do we need vaccines? Will one dose work? Do we need two? What ages do we start at? What will be the cost? What is the likely morbidity? How many hospital beds? How much oxygen is needed?”

A gifted leader

“Sheetal never loses sight of why a system matters. Many times, I have watched her be the only voice in a room saying, ‘This is academically interesting, but it won't work in practice’. That instinct to stay grounded in the real world is rarer than it sounds,” said Norman.

Systems thinking means looking at an entire public health system, leading to excessively complex models. How big will a measles outbreak be? How long will it last? What will be the cost? It takes looking at communities, income and inequalities, behaviours, risk factors such as diet and pollution, the policy framework and health system, and budgets. How best can available funds be spent?

“We have to take into account what is feasible and implementable, and it must be able to be translated into reality – that is the space in which MASHA thrives,” said Silal.

How do we secure the future?

In the room were Silal’s parents, who had flown from Durban, and who learned for the first time that when she had done her pivot into a master’s degree, she also had an offer on the table from financial leviathan Old Mutual. It was just the kind of stable job they hoped she’d secure. Instead, she’d opted to study further and change direction.

“I think we can agree it worked out happily,” she said, smiling up at her parents.

Today, she has 11 doctoral and 13 master’s candidates under her supervision, having supervised four doctoral students and 19 master’s students to graduation.

“A scientist who is also a human being cannot rest while knowledge which might be used to reduce suffering rests on the shelf”

“Sheetal is deeply committed to building capacity in Africa. Through MASHA, she has been instrumental in training and mentoring the next generation of African modellers,” said Professor Hussein Suleman, the dean of the Faculty of Science.

Silal quoted Kenyan scientist, the late Professor Calestous Juma, who had emphasised the need for  ‘building Africa’s capacity  to  solve its own problems ’.

“To all the students in the room, I want you to think about what your contribution to this world will be – as modellers, analysts, scientists … We are fortunate that we can use our work to improve the world and help people live better lives.”

Silal concluded with the words of the late Dr Albert B Sabin, developer of the oral polio vaccine: “A scientist who is also a human being cannot rest while knowledge which might be used to reduce suffering rests on the shelf.”