“As the vaccines continue to roll out, hopefully the positivity rate will be going down in the coming months,” Mara told reporters last week.
In a statement, Miller of the N.F.L. said the league would, as it did last year, follow the recommendations of local, county, state and federal public health officials, including the Centers for Disease Control and Prevention, and “continue to uphold with the advice and partnership of medical and public health experts as we look to the 2021 season.”
Trying to establish definitive causal links between a single event and a change in infection rates across a large metropolitan area is complicated. The authors of The Lancet study concede that their research only shows that two events — games with fans and increasing positive Covid-19 rates — coincided. Other events like political rallies, the reopening of colleges or holiday travel may have contributed to an increase in infections, especially in states where preventive measures like the wearing of masks were less widely adopted. Infections may have also increased because fans watched games with their friends in living rooms or at bars, gatherings that were beyond the N.F.L.’s control.
“The strength of these studies is they are showing something, but the correlations can only point out the possibilities, not the causation,” said Bruce Y. Lee, the executive director of Public Health Informatics Computational and Operations Research at City University of New York School of Public Health. “It’s not just a football game and people go home. There are all these associated activities around the game.”
To establish that N.F.L. games caused the spread of the virus, researchers would need contact tracing data on fans who attended games and then tested positive. That information is scarce, though, since many local health departments used their resources to educate the public on preventive measures and increase coronavirus testing. In Duval County, Fla., health officials said they did not study whether fans who attended Jacksonville Jaguars games were infected or whether the team’s home games increased the spread of the virus.
In part because not everyone cooperated with contact tracers’ requests, even people who attended N.F.L. games and tested positive had difficulty determining whether they got infected before, during or after the games.
Eight residents who tested positive for the virus told contact tracers that they had recently attended Cowboys home games, health officials in Tarrant County, Texas, said in November.