Even as several professional sports leagues—including Major League Baseball (MLB) and the National Basketball Association (NBA) —begin to open up stadiums to fans once again, a preprint study in The Lancet has found a correlation between National Football League (NFL) games with in-person attendance and surges of Covid-19 in surrounding areas, Ken Belson reports for the New York Times.

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Study finds link between NFL games and Covid-19 spikes

For the study, Justin Kurland of the University of Southern Mississippi and colleagues looked at the number of positive Covid-19 cases in the counties where all 32 of the NFL's teams play, as well as the surrounding counties, before and after games with and without fans in attendance. According to the study, the researchers included surrounding counties to account for fans who may have traveled farther to attend games.

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In total, the researchers assessed conditions for 269 NFL games, including 117 that had fans and 152 that were unattended.

After making adjustments to account for potential false positives and days in which counties didn't report cases, the researchers found that Covid-19 infection rates surged during the second and third weeks following NFL games that permitted more than 5,000 fans to attend.  "The evidence overwhelmingly supports that fan attendance at NFL games led to episodic spikes," the researchers wrote.

However, the researchers noted that while the study demonstrated a potential relationship between fan-attended NFL games and Covid-19 surges, it did not establish a causal link. The researchers said it was possible that other events, such as holiday travel, colleges reopening, or political rallies also could have contributed to increases in Covid-19 cases, especially in states with fewer coronavirus countermeasures in place, such as mask-wearing. Covid-19 infections rates may have also spiked because football fans gathered elsewhere, such as in living rooms or bars, outside of NFL's purview.

In light of the findings, however, the researchers recommended that professional sports leagues be cautious in welcoming fans back.

"We are not saying that the NFL shouldn't have opened up to fans," Alex Piquero, a sociologist at the University of Miami and co-author of the study, said. "But we have to understand the public health implications of opening up."

Study comes as sport leagues begin reopening to fans

According to the Times, the study comes as several professional sports leagues, such as the MLB and the NBA, are increasingly permitting limited attendance—and shortly after NFL Commissioner Roger Goodell announced plans to open the league's stadiums at full capacity in September. "All of us in the NFL want to see every one of our fans back," Goodell said.

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At the time of that announcement, Jeff Miller—the NFL's EVP for communications, public affairs, and policy—said public health officials in areas where NFL teams play had found no "case clusters" after the 119 games played with fans attending in-person last year.

Miller also cited a study done by the MIT Sports Lab, which was not published and was independently conducted, that looked at Covid-19 rates from counties surrounding areas where NFL games were plated and compared them to "synthetic" data as a control group. The researchers did not find any notable increases in Covid-19 rates "in the appreciable time frame following the games."

In addition, Miller flagged a study from the Florida Department of Health, which has not been peer-reviewed, that found that Covid-19 rates were "slightly higher" in the Tampa area in the weeks following the Super Bowl, which was hosted in the city. However, the health department determined that most of the coronavirus' transmission came "likely from private gatherings, in homes, or unofficial events at bars and restaurants."

Separately, Kevin Watler, a spokesperson for Florida's health department in Hillsborough County where the Tampa Bay Buccaneers play, said contact tracers discovered "very low numbers" of positive Covid-19 cases among those who attended Buccaneers games during the NFL season, and that researchers don't think those people spread the coronavirus to others.

Meanwhile, Rex Archer—director of health for Kansas City, Missouri, home to the Kansas City Chiefs—said health departments in the area did not detect any spread of the new coronavirus linked to attendance at Chiefs games.

However, Archer said tracking cases at bars and restaurants were harder, as some were closed while others weren't. "You could have 15,000 socially distanced fans at Arrowhead Stadium, yet some people packed into a bar," he said.

And the NFL cited a preprint study from February that found attendance at NFL games and college football games didn't have a "significant" impact on Covid-19 case rates. However, according to the Times, that study tracked only positive cases in the counties where games were held, unlike the latest study, which also examined the case rate in surrounding counties.

Ultimately, however, Miller said the NFL would follow whatever recommendations local, county, state, and federal public health officials provide and will "continue to uphold with the advice and partnership of medical and public health experts as we look to the 2021 season" (Belson, New York Times, 4/6).