  There is great interest in the dynamics of health behaviors in social
networks and how they affect collective public health outcomes, but measuring
population health behaviors over time and space requires substantial resources.
Here, we use publicly available data from 101,853 users of online social media
collected over a time period of almost six months to measure the
spatio-temporal sentiment towards a new vaccine. We validated our approach by
identifying a strong correlation between sentiments expressed online and CDC-
estimated vaccination rates by region. Analysis of the network of opinionated
users showed that information flows more often between users who share the same
sentiments - and less often between users who do not share the same sentiments
- than expected by chance alone. We also found that most communities are
dominated by either positive or negative sentiments towards the novel vaccine.
Simulations of infectious disease transmission show that if clusters of
negative vaccine sentiments lead to clusters of unprotected individuals, the
likelihood of disease outbreaks are greatly increased. Online social media
provide unprecedented access to data allowing for inexpensive and efficient
tools to identify target areas for intervention efforts and to evaluate their
effectiveness.

Social and Information Networks;Physics and Society;Populations and Evolution