▶ Watch Video: Final funeral held for victims of Nashville shooting

A new study has found that fatalities from gun violence in the U.S. have increased over time, with more victims dying at the scene of a shooting before they can be transferred to medical treatment facilities.

The research, which was published Wednesday in the Journal of the American Medical Association, examined gun violence incidents from 1999 to 2021, including firearm deaths due to assaults, unintentional injuries and unknown intent.

Using data from the U.S. Centers for Disease Control and Prevention, researchers discovered the proportion of deaths at the scene increased from about 52% in 1999, to almost 57% in 2021.

Nearly 49,000 people died from gun violence in the U.S. in 2021, according to the CDC.

The research letter summarizing the study said this increase in fatalities was likely due to several factors, including higher guns sales, social isolation during the COVID-19 pandemic, and a “lack of new federal firearm legislation.” 

The types of guns used in shootings also appeared to contribute to the increase, researchers found.  

“Studies suggest that both the risk and lethality of firearm injuries have increased, partly due to larger magazine capacity and growing use of high-caliber weapons,” the research letter read. 

A doctor who works at a hospital which treated victims of last week’s Nashville school shooting, in which six people were killed, told CBS News Tuesday that many shooting victims are not making it to hospitals before succumbing to their injuries due to the types of guns used. 

“It’s clear that there’s not a lot that we can do in the trauma rooms, unless the people get to us so that we can help save them and do what we have been trained to do,” said Dr. Jay Wellons, chief of pediatric neurosurgery at Vanderbilt University Medical Center. “The challenge is, with these really destructive weapons, we can’t do that work.”

The data used in the research did not include information about self-inflicted gun incidents, as most deaths in those scenarios occur at the scene, the study said.