Remember 2009? The H1N1 pandemic we were all waiting for? I do. I was pregnant; H1N1 was particularly risky for pregnant women. The vaccine wasn’t available until after I had my baby, but when they held a clinic an hour north of where I live, I brought my husband there so we could both get our shots. My infant son was too young to be vaccinated, so I wanted to protect him through herd immunity.
A study came out recently on twitter messages from that time. How did pro-vaccine sentiments spread, versus anti-vaccine ones? Which messages were more contagious?
I talked to one of the authors, Marcel Salathe, today. He’s an infectious disease researcher studying the spread and transmission, not (just) of disease, but of information. “We assume people infect each other with opinions about vaccinations,” he said, and the H1N1 scare was a good opportunity to put some of his group’s theories to the test.
They collected nearly half a million tweets about the H1N1 flu vaccine. In 2009, H1N1 wasn’t included in the regular flu shot, and became available partway through flu season as a separate dose. With a possible pandemic looming, people had plenty of motivation to get the vaccine and encourage others to get it—butanti-vaccine sentiments were in circulation too.
The result, striking but perhaps not surprising: negative opinions were more contagious than positive ones. (Specifically, someone who read a lot of anti-vaccine messages was more likely to follow up by tweeting or retweeting negative messages of their own.)