Midsommarfirande Nätverksforskning Foto: Kenneth Kullman/Mostphotos

Knowledge about social networks is important for understanding how illnesses spread
Photo: Kenneth Kullman/Mostphotos.


Fredrik Liljeros had his first research position as a postdoc at the former Institute for Infectious Diseases with current State Epidemiologist Anders Tegell as his direct supervisor and Johan Giesecke, former State Epidemiologist, as his departmental supervisor. At the time, SARS was the focus – a viral outbreak with a higher mortality rate than COVID-19.

Fredrik Liljeros
Fredrik Liljeros
Foto: Paul Fuehrer

"I was honestly more worried about the future back then. Partly because of the high mortality rate but also because Canada, a country very similar to Sweden, had severe difficulties during a short period."

What is network research?

Network research is an interdisciplinary research field that incorporates sociology, ecology, mathematics and physics. We all map network structures with different questions in mind, like: How did the network emerge? Why does it look like it does? What are the consequences of this?

How is it relevant to studying epidemics?

"There’s a significant variation in how important different types of contact are to spreading different diseases. Some require close contact or contact over a longer period of time, like tuberculosis or HIV. Others are extremely contagious, like measles, where one person can infect a whole lecture hall.

"COVID-19 is a disease that most often requires close contact over a longer time period to be transmitted. According to the first data coming from China, most people were infected by their own family members. Of course, it’s also important to understand the more casual, less infectious contacts outside of the closest circles because there are so many more of them.

"In the battle against transmission, simple mathematical models are often used, where everyone in a group (like a city) is assumed to have the same potential for transmission. The models function surprisingly well for very easily transmitted diseases, but less well for diseases like influenza and COVID-19.

"To understand how diseases like COVID-19 are spread and how they should be fought, we need a deeper knowledge about the structures of people’s networks and contacts. This knowledge allows government agencies to make different types of decisions about what will effectively combat transmission. Unfortunately, a lot of the studies being published now build on overly simplistic assumptions about contact networks."

What is the most important thing we’ve learned from earlier epidemics?

“That there will always be rumours, like about how the disease spreads. The situation with the COVID-19 epidemic is different from earlier because now basically everyone, young and old, uses social media. So rumours spread more easily than in the past.”

What other topics do network researchers study?

It runs the gamut. I’ve been involved in research projects that mapped the contact patterns of bees in a beehive, internet dating sites, and even criminal networks.

What are you researching now?

How contact patterns in hospitals affect the risk for illnesses to spread within and among hospitals. But for right now, a large part of my time is spent critically reviewing the relevant studies being published on COVID-19.

Fredrik Liljeros’ current research focus:

  • How infections spread within and among hospitals
  • How human interaction patterns affect the spread of disease
  • Development of mathematical models for how illnesses spread, particularly sexually transmitted diseases
  • Pandemics and studies of how actions like travel restrictions affect the speed of transmission in epidemics.

Read more about Fredrik Liljeros’ research