For at least two weeks after a gun show is held in Nevada, there is a sharp increase in gun-related deaths and injuries in communities across the state line in California, a new study published in Annals of Internal Medicine has found.

Researchers from the University of California, Berkeley, examined California death and hospitalization records from 2005 and 2013, and then looked at the 915 gun shows held in both California and Nevada over the same period. They found that in the 14 days after the start of a gun show, California hospitals within a two-hour drive from the Nevada state line experienced a 70 percent increase in admissions for gunshot wounds.

When gun shows were held in California, however, no similar increase in gun violence was recorded in surrounding communities. One likely explanation for the divergence, researchers said, is that California’s gun laws are much stricter than those in Nevada.

California is one of 13 states that requires a background check on transfers at gun shows. It also imposes a 10-day waiting period on all gun purchases. California also employs a range of security measures to deter illegal transfers, including surveillance by state law enforcement.

Nevada, on the other hand, has no background check or security requirements at gun shows; it also does not impose a waiting period.

Last November, Nevada voters narrowly passed Question 1, a ballot initiative that requires background checks on all gun transfers. But due to a dispute over who would conduct the checks — the state says it doesn’t have the capacity, and the Federal Bureau of Investigation has refused to take on the task — the new law still hasn’t been implemented. 

Two weeks ago, a group of Nevada residents filed suit against the governor and state attorney general, who opposed the measure. The National Rifle Association poured more than $6.6 million into opposing Question 1, making it the group’s second-largest campaign expenditure of 2016, after the presidential election.

“Our study suggests that California’s strict regulations — on firearms, generally, and on gun shows, specifically — may be effective in preventing short-term increases in firearm deaths and injuries following gun shows,” said the study’s lead author, Ellicott Matthay, a Ph.D. student in Berkeley’s School of Public Health.

California’s strict laws may prompt some residents seeking buy guns, and avoid scrutiny, to drive to gun shows across the Nevada border, the study’s authors also noted.

Most of the shootings following Nevada gun shows were the result of interpersonal violence, according to the findings.

A 2008 working paper from the National Bureau of Economic Research found no connection between gun violence and gun shows in California and Texas. In 2010, Garen Wintemute, a leading gun researcher and one of the co-authors of the Berkeley study, published a rebuttal of the findings, calling them “fatally flawed.”

In an editorial, two of the Berkeley study’s authors call for more research into gun violence, noting, “Our knowledge about the effect of policies regulating gun shows on firearm morbidity and mortality is severely limited.”

The “gun show loophole,” so named because gun shows are not regulated by the 1993 Brady Act, first came to prominence after the mass shooting at Columbine High School in Colorado in 1999, when it emerged that the teenage gunmen had a friend procure several of the murder weapons from a Colorado gun show. While research has found that few violent criminals obtain weapons directly from gun shows, the shows are a major source for traffickers.