The noxious clamoring of a privileged minority has grown louder on Twitter—imperiling public health, a new study warns.

The volume of dangerous tweets falsely linking life-saving vaccines to autism spiked dramatically in recent years. But the alarming uptick doesn’t necessarily represent a surge in anti-vaccine sentiments in overall public opinion. Instead, the uptick indicates the amplifying voices of very specific demographics: people from affluent, largely populated areas in just five states—California, Connecticut, Massachusetts, New York, and Pennsylvania.

The study’s authors, led by psychologist Theodore Tomeny of the University of Alabama, say the rise is worrying. But, they argue, keeping an eye on social media may help shush the misinformation at its source.

In the study, appearing in the October issue of Social Science & Medicine, they conclude:

“Monitoring social media for up-to-date anti-vaccine beliefs allows public health professionals to address such beliefs by targeting geographic areas where these beliefs are most prevalent and tailoring the approach to demographic characteristics of populations most correlated with these beliefs.”

They recommend that pediatricians take note of online trends and—if the tweets are coming from inside their areas—press the issue with patients. Tomeny and colleagues also suggest online interventions, such as a Twitterbot that scans for dangerous tweets and auto-replies with factual health information.

Twitter tripe

For the study, the researchers harvested around 550,000 tweets from January 2009 to August 2015 using keywords related to both autism and vaccines. Then they used a machine learning algorithm to sort the tweets into pro-vaccine, neutral, and anti-vaccine categories. Overall, nearly 273,000 tweets fell into the latter category. Of those, about 108,000 from 47,000 users were geo-coded—based mostly on self-disclosed locations in public profiles—to 732 micro/metro areas.

Between 2009 and 2014, the researchers found that the volume of anti-vaccine tweets was largely stable and low. But beginning in July of 2014, volume began spiking in just five states. For instance, while the monthly average across the country jumped to 250 that month, New York’s volume increased five-fold. In January of 2015, the spikes continued, with California seeing a 10-fold leap.

The flood of tweets came from areas in those states that had several demographic variables in common. The areas tended to have a relatively higher population size and higher numbers of women who had recently given birth. The areas also tended to have higher numbers of households with annual incomes equal to or more than $200,000. Last, the tweets linked to areas with higher numbers of men between 40 and 44, men who didn’t finish college, and a decrease in women aged 15 to 17.

The data largely squares with other demographic data on the anti-vaccine movement that has taken root in recent decades. Those studies consistently found that affluent, married white women with higher education and older birth age are behind the movement.

But, the state data doesn’t necessarily echo state trends. While California, Connecticut, Massachusetts, New York, and Pennsylvania were main sources of anti-vaccine falsities on Twitter, recent data from the Centers for Disease Control and Prevention found that the movement was having sway in many other states . Between 2009 and 2016, Connecticut, Florida, Iowa, Kentucky, Maryland, New York, North Carolina, North Dakota, Ohio, Oklahoma, and Virginia saw continued rises in non-medical vaccine exemptions. (California saw a decrease in exemptions in 2015 after a state ban.)

The far reach of anti-vaccine messages was evident in a massive measles outbreak in Minnesota this year. The outbreak struck in a Somali immigrant community in Hennepin county but was largely spurred by non-local anti-vaccine advocates.

Siman Nuurali, a Somali-American clinician who helped respond to the outbreak, told The Washington Post at the time:

“It’s remarkable to come in and talk to a population that’s vulnerable and marginalized and who doesn’t necessarily have the capacity for advocacy for themselves, and to take advantage of that… It’s abhorrent.”

The new study on Twitter-based messages has limitations, of course. For one thing, it didn’t look at all anti-vaccination messages, and Twitter users make up only about 23 percent of all Internet users—they’re not nationally representative by any means. Still, the authors argue, the data has value.

“Monitoring social media for anti-vaccine beliefs is beneficial for surveillance and intervention efforts to curtail anti-vaccine beliefs,” they conclude.

Social Science & Medicine, 2017. DOI: 10.1016/j.socscimed.2017.08.041 (About DOIs).