SMART NEWS

Anti-Vaccine Tweets Spread Faster Than Pro-Vaccine Messages

Not all messages are created equal, and when it comes to Tweets about vaccines it’s the anti-vaccine messages that spread the fastest

Rose Eveleth

Contributor

April 8, 2013

On Twitter, negative opinions about vaccines may be more contagious than positive ones. In a study that looked at Tweets about the 2009 H1N1 pandemic, researchers wanted to know how messages about the vaccine that helped prevent the disease spread. They found that anti-vaccine messages spread the fastest—people who were tweeting about the risks (whether real or fake) seemed to be more likely to spread messages about the vaccines than those who supported the shots.

There could be many reasons for this trend. Beth Skwarecki at PLOS Blogs asked researcher Marcel Salathe about her theory:

I asked him, is it just that people can be passionate about being anti-vaccine, but nobody is passionate about “yeah, I got my flu shot”? He says maybe not: people who are pro-vaccine are often concerned that those who don’t vaccinate are putting others at risk. On the other hand, the anti-vax folks included people who sent out hundreds of negative tweets; nobody had that kind of enthusiasm on the positive side.

Another explanation was offered by Rachel Rettner, at My Health News Daily:

t’s possible that “many people had latent negative opinions about the vaccine, and when they were intensely exposed to enough positive messages, they felt the need to express their negative sentiment,” Salathé said.

Salathe himself summarized their three key findings on his website:

1. Everything depends on context – the dynamics of negative sentiments were completely different from the dynamics of positive sentiments.

2. Negative sentiments did spread, positive sentiments did not spread.

3. What’s worse: exposure to positive sentiments would often be followed by negative sentiments

Now, there are some limits to Salathe’s method. Only 10 percent of the Tweets in this study were actually read by a human and categorized as positive or negative. The rest were then tagged by a computer trying to replicate the human’s decisions. And the H1N1 vaccine might not be representative of all vaccine messages or of public health messages in general. But it could help explain why it seems so hard to spread positive messaging about vaccines on the internet, while anti-vaccine advocates are everywhere.