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Twitter Shows Ideas Are Contagious, but Only the Bad Kind

Syringes during an H1N1 vaccination clinic at St. Barnabas Presbyterian Church in Dallas in 2009.
Syringes during an H1N1 vaccination clinic at St. Barnabas Presbyterian Church in Dallas in 2009. Photograph by Matt Nager/Bloomberg

Bad news for public health officials: Negative messages about vaccines spread through social networks, but pro-vaccine messages don’t. That’s the conclusion of a new study by Penn State researchers who analyzed Twitter messages from the H1N1 swine flu pandemic three years ago.

It gets worse. People who were exposed to a lot pro-vaccine messages—those whose social networks were basically telling them to get their flu shots—were more likely to come out with the opposite view. “If you’re intensely exposed to positive messages, we would essentially be able to predict that you would go negative, express negative sentiment,” says Marcel Salathé, a professor of biology and computer science at Penn State’s Center for Infectious Disease Dynamics.