Studying the social context of flu transmission helps manage the virus’ reach and its effects.
Shivering. Cold sweats. Nausea. A sore throat and aching muscles. A runny nose. Headaches… All tell-tale signs that the flu has arrived. For most people an infection means a few days to one or two weeks of feeling uncomfortable, wrapping oneself up in a thick blanket and sipping chicken soup. For some, however, it constitutes a death sentence. According to various estimates, the flu kills a few hundred thousand people every year. Like most predators, it generally finds its quarry among the weak, the young, and the old.
Modelling the moves of a murderer
Understanding exactly how the flu spreads could prove to be a great help in stopping it. After all, if you know where a murderer tends to hang out and how he or she chooses victims, it’s easier to stop the killing spree. An individual’s risk to land in the cross-hairs of a pathogen like the flu depends on several factors, such as the nature of the virus, the immune system of the potential host, and the behavior of infected people. Studying the impact of social behavior on flu transmission can help us to anticipate the reach of the virus and moderate its effects.
One way to approach this is to model the movements of the perpetrator, which is exactly what a team of ‘virus profilers’ has done. Spearheaded by Dr. Adam Kucharski from the London School of Hygiene & Tropical Medicine and Imperial College, the international team developed various models with which to assess infection risk. In the models, they divided the population in different age groups, contact classes, or a mixture of both. This framework allowed them to tweak the number and breadth of the included age and contact groups. Then, they unleashed a virtual flu epidemic. To choose the best model, they compared each one with real data from the 2009 flu epidemic in Hong Kong.
Profiling a virus
So, how did the killer move among its victims? Well, according to their comparison, the best supported model for the Hong Kong data had 20 age groups and included only close contacts of the infected individuals. More precisely, the risk of infection is not so much about what individual people report themselves about their social contacts, as it is about the average social behavior of the entire age class they belong to.
With the assistance of their top model, the scientists also revealed the flu’s preferred victims. It turns out that this particular strain sought out the young and their parents. The murderer moved a lot by way of intense contacts between those under 18 years of age. In young adults the risk of infection dropped, only to rise again in those aged between 35 and 50, a period in life often marked by having and raising children. Kids, through interaction with their buddies and parents, were the main route of transportation used by the viral assassin.
The many guises of a killer
And yet, despite the efforts of this team and others, the flu continues to claim many victims. Fortunately, the researchers are aware of their study’s limitations. Firstly, they only used data from the Hong Kong epidemic. Both differences in the composition of the infected population and in the prevalent flu strain can affect how the disease spreads. Also, a person’s behavior was assessed using a one-day contact survey. A longer monitoring period might capture significant behavioral changes over time.
Nevertheless, this study represents an important step in figuring out how the flu moves among its victims and how that information can be used to stop it from turning into a full-fledged epi- or pandemic. This investigation shows that knowing the average social behavior of different age groups is a crucial bit of knowledge. Fortunately, this bit is fairly easy to obtain through self-reports of potential victim groups. Coupling that with data on the population’s composition can be very useful in catching this killer red-handed, even with limited resources, as it allows better and more cost-effective targeting of intervention measure such as vaccination campaigns.
While the hunt is far from over, this is another stride towards containing the influenza villain. One day, flu, we’ll stop you once and for all.
Kucharski, A., Kwok, K., Wei, V., Cowling, B., Read, J., Lessler, J., Cummings, D., & Riley, S. (2014). The Contribution of Social Behaviour to the Transmission of Influenza A in a Human Population PLoS Pathogens, 10 (6) DOI: 10.1371/journal.ppat.1004206