Scientists use Google search data to show reduction in chickenpox outbreaks

Scientists have used Google search data to show how vaccination against chickenpox has significantly reduced seasonal outbreaks of the common childhood disease. Researchers analysed thousands of Google searches for "chickenpox," downloaded from the Google Trends data of 36 countries on five continents, covering an 11-year period starting in 2004.

The technique is called digital epidemiology and has previously been used to identify outbreaks of diseases like influenza, rotavirus and norovirus. The new study is the first to use digital epidemiology to show the effectiveness of a vaccine, said Kevin Bakker, doctoral student at the University of Michigan in the US. 

The approach offers a novel way to track the global burden of childhood diseases and to illustrate the population-level effects of immunisation - especially for diseases like chickenpox where clinical case data are scarce. However, the technique is limited to countries where Internet service is widely available.

Examining data from several dozen countries enabled the researchers to identify the seasonality of chickenpox outbreaks, which occurred in the springtime worldwide, Bakker said.The main idea behind digital epidemiology studies is that the number of Google searches spikes in response to an infectious-disease outbreak as worried parents and others seek information about symptoms, treatment, vaccines and related topics.

To demonstrate that Internet queries about chickenpox can be used as a reliable proxy for disease incidence, Bakker and his colleagues had to show that Google Trends data accurately reflected clinical cases. However, chickenpox is not included in the World Health Organisation's global monitoring system for vaccine-preventable diseases, and only a handful of countries report cases to national-level public health officials.

Researchers found that in the three countries that require reporting of chickenpox cases but do not require vaccination against the disease - Mexico, Thailand and Estonia - Google searches for "chickenpox" were strongly correlated with reported cases.

In the US and Australia, two countries that report chickenpox and require the vaccine, the correlation still held but was weaker. These correlations enabled the researchers to create a forecasting model to predict the timing and magnitude of chickenpox outbreaks based on Google Trends data. "These results suggest that information seeking can be used for rapid forecasting, when the reporting of clinical cases is unavailable or too slow," researchers said.

The study was published in the journal PNAS.