When a mass shooting happens, another often follows in close succession. That’s not just a feeling ― it’s a fact.
The devastating shooting on May 24 in Uvalde, Texas, which killed 19 children, two teachers, and injured 17 others, occurred 10 days after a supermarket shooting in Buffalo, New York, which resulted in 10 deaths. In 2021, a shooting at a massage parlor in Atlanta, which left eight dead, came less than a week before a shooting at a supermarket in Boulder, Colorado, that killed 10. And a 2019 shooting in Dayton, Ohio, on August 4 that killed nine people took place only a day after a Walmart shooting in El Paso, Texas, which claimed 22 lives.
Researchers argue that the clustering of mass shootings suggests that this type of violence spreads like a virus and should be treated as one.
This theory ― called the “contagion effect” ― has been examined at length in cases of suicide, especially among teens and young adults. Studies have demonstrated that the majority of adolescents who attempt suicide have previously been exposed to the suicidal behavior of a peer.
In many cases, mass shootings are also suicides, with shooters taking their own lives at the time of the shooting or not long after.
“They have literally and figuratively given up on their life as they know it.” said Joel Dvoskin, PhD, a clinical and forensic psychologist at the University of Arizona, Tucson, and former acting commissioner of mental health for New York state.
According to contagion theory, mass shootings ― and the round-the-clock media coverage they generate ― lead to even more killings.
A team of researchers at Arizona State University led by Sherry Towers, PhD, analyzed mass shooting data in 2015 to find out whether those events followed a similar pattern. Towers spent much of her career modeling the spread of infectious diseases, such as influenza, Ebola, and Zika.
Towers and her colleagues discovered that a mass killing tended to give rise to more killings in its immediate aftermath. According to her evaluation of USA Today’s mass shooting database, a second incident was most likely to occur within 13 days of the initial event.
What Defines a Mass Shooting?
The FBI defines a mass shooting as any incident in which four or more people die by gunfire. That definition, however, is not universally accepted. The lack of a standard definition complicates the the work of researchers who study contagion theory.
Mother Jones magazine created an open-source database of mass killings that employs a similar definition but that includes only incidents that involve a person shooting indiscriminately in a public place.
With this narrower definition, shootings involving organized crime, robberies, and domestic violence ― which make up the vast majority of shootings in which multiple fatalities occur in this country – are excluded. Events such as those that occurred in Sandy Hook or the killings in Highland Park, Ill inois, this past July would be included.
The Gun Violence Archive categorizes mass shootings as any incident in which four or more people are shot but not necessarily killed, while Everytown for Gun Safety tallies mass shootings that take at least four lives.
Medscape used these three databases to depict how dissimilar the data can be, depending on which definition of mass shooting is used.
James Meindl, PhD, a professor of behavioral analysis at the University of Memphis who studies mass shootings, said parsing the differences between what happened in Uvalde and what happens during a shooting involving organized crime or domestic violence is crucial when thinking about intervention and prevention.
“If you want to intervene, you have to know why the person engaged in this behavior in the first place,” Meindl said. “The factors that led a person to commit gang violence, the factors in domestic violence, the factors in indiscriminate mass shootings ― those are all very different factors that would call for very different interventions.”
So, Should Mass Shootings Be Treated Like an Infectious Disease?
Rather than using contagion theory, Meindl said he prefers to view mass shootings through the lens of “generalized imitation,” a psychological concept involving the learned ability to mimic behaviors observed either in person or through the media. Behaviors “are not diseases that can spread on contact,” he said.
“The more you’re exposed [to violence], the more likely you are to repeat it, just like the more you’re exposed to COVID, the more likely you are to get it and give it to somebody else,” Slutkin said. And just as people have varying degrees of susceptibility to COVID-19 and other infectious diseases, Slutkin argued that some are more susceptible to committing a mass shooting, depending on their level of isolation, personal “grievances, and their need for belonging or credit.”
To Slutkin, mass shootings ― and other forms of violence ― should be treated with the standard methods that public health officials would use to stop the spread of a contagious disease: detection and interdiction that would put a stop to potential events. The nonprofit organization that he founded, Cure Violence Global, employs “violence interrupters” to reach out to and engage with community members who might be at risk of being a victim of violence or of committing an act of violence, much as a public health worker would approach epidemic control.
Research conducted on the effects of this method of reducing rates of violence suggests the approach works. In 2017, New York City saw a 63% reduction in gun injuries, according to a study from the John Jay College of Criminal Justice. And after evaluating the effects of this approach in Chicago in 2014, researchers from the University of Illinois and the University of Chicago determined that there was a 19% reduction in shootings in the city.
“The results of stopping an epidemic come really fast,” Slutkin said. “But getting people to switch gears to the right kind of treatment happens really slowly.”