Faculty Spotlight: C. Jessica Metcalf

Written by
Aimee Bronfeld
Sept. 23, 2020

Jessica Metcalf, Associate Professor of Ecology, Evolutionary Biology and Public Affairs, spent 18 years in Africa before heading to college and launching her academic career. She resided in several different countries, although it was probably Madagascar that affected her most. Located about 250 miles off the continent’s southern coast, the island is widely regarded as an ecological paradise. Unlike anywhere else on earth, approximately 90 percent of the country’s wildlife is endemic showcasing a brilliant assortment of birds, reptiles, amphibians, and flora while making it the ideal training ground for an aspiring biologist.

In a recent interview, Professor Metcalf chronicles her passage from the shores of Madagascar to the front lines of global health. A demographer with broad interests in evolutionary ecology, infectious disease dynamics, and public policy, her research has surged into the limelight as the scientific community confronts Covid-19. At the same time, Professor Metcalf has assumed a new role as co-director of the Global Health Program at the Center for Health and Wellbeing.

Q. Madagascar has been called a naturalist’s wonderland.  I’d imagine that growing up in a place like that inspired your interest in biology.  Was that the case?

A. Absolutely. Living in Madagascar at that time in my life, from the age of 14, very much led to my excitement about biology. Madagascar has such unbelievably spectacular biodiversity. I was particularly passionate about the reptiles. The island has the largest diversity of chameleons in the world, as well as an incredible diversity of frogs. And, of course, there are the lemurs… more than 100 native species.

I took a gap year before college, in fact, to explore my interest in biology. I worked for various academics, from the large research groups focusing on the lemurs to graduate students studying frog behavior, which was an incredible opportunity.

Q. You earned your Bachelor’s degree from University of Oxford and doctoral degree from Imperial College London, both in Biology, before conducting postdoctoral research at several institutions, including Princeton. How did these experiences shape your aspirations?Given the unique landscape of Madagascar and your aspirations, why did you leave the isl the United Kingdom?

A. When I first started my undergraduate degree, I was excited thinking about the extraordinary biodiversity of Madagascar. I did a few projects on marine turtles and chameleons, and I really loved them. But I also felt a little bit overwhelmed by some of the logistical challenges, inequalities, and complexities of life in those settings. I wanted to do something quite removed from the pragmatic and was attracted to academia. 

For my Ph.D., I started developing quantitative skills – generally based around demography, but demography for questions related to evolution in plants, and I built on this during subsequent postdoc experiences. Then there came a stage in my life where I wanted to take these skills and do something more applied. That’s when I moved into thinking about infectious disease dynamics, specifically into thinking about vaccination policy for rubella.

Q. Tell me more about this area of concentration. What captivated your interest in infectious diseases, and why did rubella become a centerpiece of your research?

A. It was partly attributed to a sense of responsibility. Also, there is so much fascinating ecology tied in with how infectious diseases spread through landscapes. You could say it was a package of an incredibly interesting set of intellectual problems, which tapped into all of my training to that point, and the potential to contribute to reducing disease burdens and impacting health.

Rubella is the infection they thrust at you if you are a demographer because it has a unique profile of burden. If you’re infected as a child, the infection tends to be very mild. It looks a lot like measles, with spots and a fever, but unlike measles it very rarely has serious health outcomes. Also, like measles, it is completely immunizing – meaning that once you’ve had it, you never have it again. The challenge comes when women are infected during the early months of pregnancy, putting them at risk of giving birth to a child with congenital rubella syndrome, which can involve deafness, blindness, and cognitive problems. That occurrence is a tragic yet completely preventable outcome because we have a very inexpensive, effective, safe vaccine for rubella. Successful population vaccination strategies, however, are somewhat dependent on the age at which women are having children, rates of birth, rates of compliance, and other factors. That was the first problem I started working on as a postdoc at Princeton.

Q. Could you elaborate more on what it means to be a demographer and how your work intersects with other fields, particularly within the context of public health?

A. When pursuing my Ph.D., I was careful to choose a branch of biology that would equip me quantitatively. I wanted to be able to go beyond descriptions, to build models that allowed me to ask larger questions within the context of ecology and infectious disease dynamics. Demography provides familiarity with a set of tools for understanding the present and projecting forward… for predicting the consequences of changes in rates of birth and death, and for studying population trends that impact public health. Those steps sound really simple and categoric, like accounting, but counter-intuitive results often bubble up.

Let’s go back to the rubella example. I shared three important facts about the disease: it is only a problem for women of child-bearing age; it tends to be mild in children; and it is completely immunizing. Our models tell us that if you don’t vaccinate anyone at all, children are typically infected by age 9, and then they’re no longer at risk because they are immune. By chance, some women may escape infection at this young age and are still at risk of being infected during pregnancy. Consequently, some children are likely to be born with congenital rubella syndrome every year. It seems straightforward to conclude that introducing vaccination into a population is always a good thing, as this will protect these women from infection, but let’s think about what that really means. If you vaccinate most people, you make the infection rare. As a result, it will probably take longer to bump into an infected person and the average age of infection likely rises from around 9 years to perhaps 15 or 20 years – which is when females are beginning to have children. So even though you’ve decreased the total number of cases, you’ve increased risk for the one population you don’t want to get infected. That’s quite counter-intuitive, right?  As a demographer, I collect data that is used by epidemiologists and experts in other fields to evaluate whether rubella-containing vaccines should or should not be introduced in various countries around the world, in tandem with other work evaluating vaccination programs.

Q. Why did you join the faculty at Princeton?

A. After completing my postdoc, I accepted a joint appointment with the Department of Ecology and Evolutionary Biology (EEB) and the School of Public and International Affairs (SPIA), which was kind of perfect for me. I like asking esoteric, academic sounding questions along with pointed, practical questions, so the combination of these realms is great.

On the biology side, I sought the opportunity to work with Bryan Grenfell [Kathryn Briger and Sarah Fenton Professor of EEB and Public Affairs], a leading light in infectious disease dynamics, and Andrea Graham [Professor of EEB], who is primarily an evolutionary immunologist and one of the most accomplished researchers in the field, as well as many other brilliant faculty members. SPIA also fulfilled my desire for access to academics who think hard about using the best possible information for shaping public policy,

Q. Tell me about your affiliation with the Center for Health and Wellbeing (CHW), and why the center aligns so well with your research interests.

A. CHW was important to me from the beginning. The center funded one of my first research projects studying measles and rubella vaccines in Madagascar, which proved to be foundational for a lot of my work.

It is wonderful having such a diverse group of scholars thinking around issues of health and wellness – a community I can draw on for different perspectives in support of my research about infectious disease dynamics. It’s been a lynchpin in that sense.

Q. This semester, you assumed a leadership role as co-director of Princeton’s undergraduate certificate program in Global Health and Health Policy. Perhaps you could comment on the program’s escalating presence, as the world fights a formidable pandemic, and how the program can continue to thrive despite such challenges as distance learning and travel restrictions?

 A. The year 2020 has made it clear that our health here in the United States is tied to the health of everybody on the planet, while also raising issues of diversity and equity. The Global Health Program is designed to help students think critically about the data we can collect and use to spot patterns and look at global health from many different angles. 

The past several months has been fascinating as well as tragic. We’ve learned something new about Covid-19 just about every week, both revealing the urgency of the health crisis and bringing rich opportunities for sharpening how we think about global health and equity. Although we’re not on campus, we can discuss discoveries in real time and engage speakers from all over because we’re not geographically restrained. We can also redesign courses to think deeply and broadly about the state of the world during a global pandemic.

Q. Covid-19 has come to the forefront of research in medical, scientific, and academic communities. How can you and other demographers contribute to our understanding of this novel infection?

A. Data is the bedrock of everything we can do when confronting a pandemic. There have been enormous efforts to collect wide sweeps of data, at impressive speeds, particularly on patterns of incidence and health outcomes across age and sex. This information will be very useful to scientists, clinicians, and policy makers as they build strategies for controlling spread, developing an effective vaccine, and treating the virus.

One of the great societal challenges right now, for instance, is the closure of schools. We still don’t know how much children are affected by Covid-19 and how likely they are to spread the infection. Closing schools mitigates transmission but, like all other interventions, it comes with huge costs. We don’t have a very good quantification yet of what these costs and benefits are. As demographers, we can curate data to measure and weigh possible outcomes, and support decisions about when and how to safely reopen schools in each community.

Q. The Metcalf Lab is leading several projects related to Covid-19.  Could you share a few areas of focus?

A. Sure. Benjamin Rice, a Princeton Presidential Postdoctoral Research Fellow, is heading the charge to map the potential pace and burden of Covid-19 in Sub-Saharan Africa, an effort that unites a large and diverse group of collaborators. We collected data to look at anomalies in mortality and various risk indicators to estimate the pandemic’s diverse impact on different countries. Our research takes a holistic perspective, considering such factors as age profile and co-morbidities, which vary remarkably according to geography. As part of the project, we created an on-line interactive tool that projects the number of deaths and hospitalizations in each country based on demographic structure, infection fatality rates, and cumulative infection rate.

Another member of my lab, Fidisoa Rasambainarivo, spearheaded efforts to create a Covid-19 “dashboard” for Madagascar, the only one available so far. I am extraordinarily proud of this work, which was done as a public service so the people of Madagascar can see current case counts across the country.

My graduate student, Ian Miller, led research for a paper about the disease and health care burden of Covid-19 in the United States. This investigation combined the age profile across various counties with the distribution of hospitals to map projections of the cumulative case burden and the resulting burden on health care systems. Published findings highlight the importance of ensuring equitable and adequate allocation of medical care and public health resources, particularly for communities outside of major urban areas.

Q.  What’s ahead? Will Covid-19 remain at the forefront of your research in the coming months, or will you shift attention to other public health issues?

A. It’s hard not to focus on Covid-19, given its extraordinary impact on global health and the enormous opportunity for research.

My lab plans to further explore differences between male and female immune function, as Covid-19 seems to be much worse in men, as well as the concept of landscape immunity. Characterizing immunity acquired via vaccination and natural infection is a central tool for public health.

We’re also thinking about the secondary effects of the pandemic, such as how Covid-19 may have disrupted other vaccination programs and how non-pharmaceutical interventions are affecting other infections out there, like the flu – which is not enjoying all of this social distancing. As a result, we may see less transmission during the upcoming flu season and a significant drop in cases.  

There is so much we have yet to learn about this pathogen and, more broadly, about the fundamental workings of the immune system. The human immune system is incredibly complicated – and among the most puzzling pieces of biology. We have many questions to answer and problems to solve. Its mysteries will keep us busy well into the future.