Digital Epidemiology Reveals Global Childhood Disease Seasonality and the Effects of Immunization

Public health surveillance systems are important for tracking disease
dynamics. In recent years, social and real-time digital data
sources have provided new means of studying disease transmission.
Such affordable and accessible data have the potential to offer
new insights into disease epidemiology at national and international
scales. We used the extensive information repository Google
Trends to examine the digital epidemiology of a common childhood
disease, chicken pox, caused by varicella zoster virus (VZV), over an
eleven-year period. We (1) report robust seasonal information seeking
behavior for chicken pox using Google data from 36 countries,
(2) validate Google data using clinical chicken pox cases, (3) demonstrate
that Google data can be used to identify recurrent seasonal
outbreaks and forecast their magnitude and seasonal timing, and (4)
reveal that VZV immunization significantly dampened seasonal cycles
in information seeking behavior. Our findings provide strong
evidence that VZV transmission is seasonal and that seasonal peaks
show remarkable latitudinal variation. We attribute the dampened
seasonal cycles in chicken pox information seeking behavior to VZV
vaccine-induced reduction of seasonal transmission. These data
and the methodological approaches provide a novel way to track the
global burden of childhood disease, and illustrate population-level
effects of immunization. The global latitudinal patterns in outbreak
seasonality could direct future studies of environmental and physiological
drivers of disease transmission.