STANFORD (US) — When it comes to infectious disease, who and how many get inoculated isn’t as important as knowing how people interact with each other—whether they’re vaccinated or not.
In order to follow and better understand how viruses spread through real-life social networks, a group of researchers used wireless sensors to track high school students, teachers, and staff members throughout one day during the height of last January’s swine flu outbreak.
“Do you know how many contacts you have with infectious people on a daily basis? Do you know how many contacts you have with anybody on a daily basis?” says James Holland Jones, associate professor of anthropology at Stanford University.
“Very often, those are the things we know the least about because they’re the hardest to measure.”
Previously, epidemiologists have tried to answer those questions through pen-and-paper surveys, asking individuals to rely on shaky memory and vague recollections to recall who they were in contact with on any given day.
The work is detailed in the Proceedings of the National Academy of Sciences.
For the study, each teacher, student, and staff member at an unnamed American high school was outfitted with credit card-size gadgets that transmitted and received radio signals every 20 seconds during one day.
The devices logged more than 760,000 incidents when two people were within 10 feet of each other, roughly the maximum distance that a disease can be transmitted through a cough or sneeze.
“The enormous amount of interactions that occur in a single day is mind-blowing,” says Marcel Salathé, now an assistant professor of biology at Pennsylvania State University.
So are the chances to catch a cold.
After collecting the electronic tracking data, the researchers ran thousands of simulations of what would happen if there were a flu outbreak in the school.
They asked what would happen if there were enough of a vaccine to inoculate only a fraction of the school’s population. Would it be better to vaccinate teachers or students?
Would it make sense to vaccinate the more popular students, thinking they might have more interactions than their classmates who keep to themselves? Or would it be best to vaccinate a random sample of the population?
“Almost nothing was better than the random strategy unless you measure who interacts with who and for how long in a typical day,” Salathé says.
“That flies in the face of what most people might think—that the super-popular kids with more connections than everyone else are more likely to spread more of the virus.
“But it doesn’t matter if you’re a teacher or a student or a staff member, or whether you’re popular or not. Everyone’s pretty much the same when it comes to transmission of the flu.”
The information gleaned from the high school experiment could be helpful in putting the brakes on the spread of flu in a place like a school, where outbreaks sometimes lead to the closure of an entire facility.
But Salathé stresses that authorities must consider the medical, social, and ethical ramifications of doing what they did—tracking the movements and whereabouts of an entire population—on a larger scale.
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