Countries that implement government-mandated vaccinations for chickenpox see a sharp drop in the number of Google searches for the common childhood disease afterward, demonstrating that immunization significantly reduces seasonal outbreaks.
That's one of the findings from a new University of Michigan-led study that analyzed thousands of Google searches for "chickenpox." The researchers downloaded and analyzed freely available Google Trends data from 36 countries on five continents, covering an 11-year period starting in 2004.
The technique is sometimes called digital epidemiology and has previously been used to identify outbreaks of diseases like influenza, rotavirus and norovirus. But the chickenpox study is the first to use digital epidemiology to show the effectiveness of a vaccine, said Kevin Bakker, a doctoral student in the U-M Department of Ecology and Evolutionary Biology.
"It is really exciting to see human information-seeking behavior—Google searches—being reduced by vaccination implementation," Bakker said. "It's a very clear signal, and it shows that the vaccine is having a strong effect."
He said the approach offers a novel way to track the global burden of childhood diseases and to illustrate the population-level effects of immunization—especially for diseases, like chickenpox, where clinical case data are scarce. However, the technique is limited to countries where internet service is widely available.
Bakker is lead author of a paper on the topic published online May 30 in the Proceedings of the National Academy of Sciences. The work will also be a chapter in his doctoral dissertation.
The study is one of the most comprehensive digital epidemiology efforts to date, Bakker said. Examining data from several dozen countries enabled the researchers to identify the seasonality of chickenpox outbreaks, which occurred in the springtime worldwide, he said.
Among Bakker's coauthors is 2015 EEB alumnus Micaela Martinez-Bakker, who is currently a postdoctoral fellow at Princeton University.