The National Football League (NFL) held a mostly normal 2020-2021 season this year amid America's coronavirus epidemic. Sure, there were relatively low or obsolete numbers of spectators, hefty fines for not wearing masks on the sidelines, delayed games, and a rash of injuries early on, but—if you consider that many other professional sports leagues in America held or finished out their seasons in bubbles or with reduced travel—the NFL's season felt much more like a pre-pandemic "normal."

But as normal as this NFL season may have looked from the outside, the season was drastically different for players and staff, who had to adhere to a long list of intensive protocols aimed at curbing possible transmission of the novel coronavirus, including mask mandates, regular testing, quarantine requirements, and more. To evaluate whether these protocols worked, the NFL teamed up with CDC, which this week released a report on its findings from tracking the NFL's pandemic season. Here's what CDC learned from the project—and whether those lessons can help other industries.

Inside NFL's Covid-19 season, though the eyes of CDC

According to CDC, the NFL kicked off its 2020-2021 season in July 2020 with "extensive mitigation and surveillance measures in facilities and during travel and gameplay." Those measures "included mandatory masking; physical distancing; frequent handwashing; facility disinfection; restricted facility access; and regular, frequent testing of players and staff members," CDC researchers wrote in the report.

In addition, the NFL trained staff to conduct contact tracing using interviews with players and staff and data from KINEXON wearable proximity devices. The NFL required players and staff to wear the devices when they were in team environments, and the devices collected data on both the "consecutive and cumulative minutes/seconds of interactions among persons within" six feet of each other, the researchers wrote.

Over the course of the season, the NFL evaluated and tweaked those mitigation measures "based on data from routine reverse transcription–polymerase chain reaction" (PCR) tests for the novel coronavirus, the "proximity tracking devices," and "detailed interviews" with players and staff, CDC researchers wrote.

For instance, the researchers noted that, midseason, the NFL discovered that coronavirus transmission had occurred among people who had less than 15 minutes of cumulative interaction with each other. At that point, the organization revised its definition of who was considered a "high-risk contact" of someone who'd tested positive for the virus to take "mask use, setting, and room ventilation," as well as "proximity and duration of interaction" into consideration.

In addition, the NFL "developed an intensive protocol that imposed stricter infection prevention precautions when a case was identified at an NFL club," the researchers wrote. That protocol involved closing eating areas at the facilities, strict mask requirements, and requiring high-risk contacts of individuals who tested positive for the novel coronavirus to quarantine.

Between Aug. 9, 2020, and Nov. 21, 2020, the NFL conducted a total of 623,000 PCR tests for the novel coronavirus among roughly 11,400 players and staff, and the organization identified a total of 329 cases of the virus. According to CDC, after initial screenings performed in August and September, the NFL identified about 10 new coronavirus cases per week for the following seven weeks. During that time, the NFL's "standard [coronavirus] protocol was in effect, which emphasized physical distancing, masking, limited numbers of persons in specific areas, and other important behavioral and facility-related parameters," the researchers wrote.

But from Sept. 27, 2020, through Oct. 10, 2020, the NFL identified a total of 41 cases of the virus among players and staff, and 21 of those cases were believed to have come from transmission within one football club. The NFL required that club to close its facilities, and contact tracers later determined that multiple instances of transmission occurred between people who had less than 15 minutes of cumulative interaction within six feet of each other—including some that had no more than five minutes of cumulative interaction within six feet. According to the researchers, "[i]nterviews revealed that, among the brief interactions that did occur, some were during unmasked meetings in small rooms or while eating."

That's when the NFL implemented league-wide changes that began requiring teams to adhere to more intensive protocol for seven days after a player or staff member tested positive or if the team had played a game against an opposing player who's game-day test came back positive the following day. The CDC researchers noted that, from Oct. 1, 2020, to Nov. 21, 2020, a total of 29 teams had to adhere to the more intensive protocol, with teams spending a combined total of 431 days under the protocol.

The NFL also ramped up testing across the league from six days per week to seven and expanded contact tracing with its new definition of high-risk contacts. According to the CDC researchers, under the NFL's new definition, "[d]esignation of a high-risk contact generally required concern by medical experts about the interaction involving two or more components; mask use and outdoor settings were considered protective." For instance, the researchers wrote, "short car rides with partial mask use were considered high-risk, whereas prolonged interaction … in well-ventilated settings (e.g., outdoors) with proper mask use were not."

According to the CDC researchers, the intensive protocol "effectively prevented the occurrence of high-risk interactions, with no high-risk contacts identified for 71% of traced cases at clubs under the intensive protocol." Overall, the researchers found that from Oct. 15, 2020, to Nov. 21, 2020, the NFL required 189 players and/or staff who were considered high-risk contacts of someone who'd tested positive for the novel coronavirus to quarantine. Ultimately, according to CDC, 20 of those players and/or staff tested positive for the novel coronavirus during that period, but no additional "within-club spread" from those individuals occurred.

Lessons learned

Overall, CDC found that the NFL's "[i]ntensive mitigation protocols effectively reduced close interactions" among players and staff, which may have helped to keep coronavirus transmission at bay.

According to CDC, the biggest takeaway from the NFL's pandemic season was that the NFL saw coronavirus transmission occur between people who had less than 15 minutes of cumulative interaction with each other—an observation that might need a little more context for understanding why CDC deemed it so important.

Up until October 2020, CDC had defined a person having "close contact" with a someone infected with the novel coronavirus as a person who had spent more than 15 consecutive minutes within six feet of an infected individual. However, CDC in October updated that definition, and the agency now defines a "close contact" as a person who has spent a cumulative 15 minutes or more within six feet of an infected individuals across a 24-hour period—meaning those 15 minutes of exposure did not have to occur consecutively, but could occur cumulatively throughout different, shorter points of contact over the course of a day.

But in the NFL's case, CDC discovered that there were cases of coronavirus transmission among people who had less than 15 minutes of cumulative interaction with each other, meaning that even CDC's revised definition of a "close contact" might need revisiting. As CDC notes, the finding led the NFL to update its "definition of a high-risk contact" so that the definition accounted for "mask use and ventilation in addition to duration and proximity of interaction."

Can other industries follow the NFL's lead?

CDC said its findings have some implications for broader public health measures intended to curb the novel coronavirus's spread, particularly among "essential workplaces, long-term care facilities, and schools."

For example, CDC said the findings could help to improve contact tracing efforts. "Assessment of the context of each interaction, including mask use, indoor versus outdoor setting, and ventilation, in addition to duration and proximity, can improve identification of high-risk contacts during contact tracing," the researchers wrote.

In addition, CDC said its findings demonstrate that implementing quarantine requirement for high-risk contacts could help to curb the novel coronavirus's transmission. "Postexposure quarantine based on redefined high-risk criteria, combined with testing and environment-specific intensive protocols, can protect communities before and after case identification," the CDC researchers wrote.

But there are challenges to implementing those protocols in settings beyond the NFL.

For one, as the CDC researchers noted, the NFL used both proximity devices and "prompt, detailed contact tracing" to identify high-risk contacts of people who'd tested positive for the novel coronavirus. But many Americans are resistant to public health officials using both location data and contact tracing to mitigate the virus's spread, meaning those strategies may not be as effective among the broader population.

In addition, the NFL's protocols relied on strict mask requirements, regular coronavirus testing with next days results, and closing down eating areas—all areas where America has struggled in its response to the epidemic, largely due to Americans' unwillingness to follow the public health measures and long-spanning issues with testing capacity.

Lastly, as the CDC researchers note, the NFL's protocols "were resource-intensive"—and they were also costly. For instance, as Axios' Kendall Baker and Jeff Tracy report, the NFL anticipated spending around $75 million on testing alone, which is a hefty price tag that many workplaces, health care facilities, and schools may not be able to match.