MMWR, Results from a Test-to-Release from Isolation Strategy Among Fully Vaccinated National Football League Players and Staff Members with COVID-19

Morbidity and Mortality Weekly Report

MMWR / February 25, 2022 / Vol. 71 / No. 8 299

US Department of Health and Human Services/Centers for Disease Control and Prevention

Results from a Test-to-Release from Isolation Strategy Among Fully Vaccinated

National Football League Players and Staff Members with COVID-19 —

United States, December 14–19, 2021

Christina D. Mack, PhD

; Erin B. Wasserman, PhD

; Marie E. Killerby, VetMB

; Rieza H. Soelaeman, PhD

; Aron J. Hall, DVM

;

Adam MacNeil, PhD

; Deverick J. Anderson, MD

; Patti Walton, MHSA

; Saamir Pasha, MPH

; Emily Myers

; Catherine S. O’Neal, MD

;

Christopher J. Hostler MD

; Navdeep Singh, MD

; Thom Mayer, MD

Allen Sills, MD

During December 2021, the United States experienced a

surge in COVID-19 cases, coinciding with predominance of

the SARS-CoV-2 B.1.1.529 (Omicron) variant (1). During this

surge, the National Football League (NFL) and NFL Players

Association (NFLPA) adjusted their protocols for test-to-release

from COVID-19 isolation on December 16, 2021, based on

analytic assessments of their 2021 test-to-release data. Fully

vaccinated* persons with COVID-19 were permitted to return

to work once they were asymptomatic or fever-free and experi-

encing improving symptoms for ≥24 hours, and after two nega-

tive or high cycle-threshold (Ct) results (Ct≥35) from either of

two reverse transcription–polymerase chain reaction (RT-PCR)

tests

†

(2). This report describes data from NFL’s SARS-CoV-2

testing program (3) and time to first negative or Ct≥35 result

based on serial COVID-19 patient testing during isolation.

Among this occupational cohort of 173 fully vaccinated adults

with confirmed COVID-19 during December 14–19, 2021,

a period of Omicron variant predominance, 46% received

negative test results or had a subsequent RT-PCR test result

with a Ct≥35 by day 6 postdiagnosis (i.e., concluding 5 days

of isolation) and 84% before day 10. The proportion of

persons with positive test results decreased with time, with

approximately one half receiving positive RT-PCR test results

after postdiagnosis day 5. Although this test result does not

necessarily mean these persons are infectious (RT-PCR tests

might continue to return positive results long after an initial

positive result) (4), these findings indicate that persons with

* Fully vaccinated was defined as ≥14 days after primary vaccination series

completion, with or without a booster. Partially vaccinated was defined by NFL

as receipt of 1 dose of a 2-dose series or <14 days after primary vaccine series

completion. Under NFL-NFLPA protocols, persons with 1 dose of a 2-dose

mRNA vaccination series and a documented history of COVID-19 were subject

to the same requirements as were fully vaccinated persons in the NFL-NFLPA

protocols; however, these persons were excluded from analyses summarizing

the test-to-release from isolation strategy.

†

SARS-CoV-2 tests included either laboratory-based real-time RT-PCR

(BioReference Laboratories RT-PCR assay [Roche Cobas assay, Roche]) or point

of care (POC) RT-PCR (Mesa Biotech Accula SARS-CoV-2 test, Mesa Biotech

Inc.). The Roche Cobas RT-PCR test used received Food and Drug

Administration (FDA) Emergency Use Authorization as a qualitative diagnostic

assay with a Ct cutoff of >40. Use of this assay with alternative Ct cutoffs is

not authorized by FDA. The Mesa Biotech Accula test produces a qualitative

result (positive/negative) without Ct values.

COVID-19 should continue taking precautions, including cor-

rect and consistent mask use, for a full 10 days after symptom

onset or initial positive test result if they are asymptomatic.

The NFL consists of 32 member clubs based in 24 states.

NFL required COVID-19 vaccination (as of June 7, 2021)

and boosters (as of December 27) for staff members who

directly interact with players and incentivized but did not

require vaccination among players. By October 13, 2021, the

NFL population vaccination rate was >96% (staff members

>99%; players >94%) (5). For most of the 2021 season, fully

vaccinated persons were tested weekly and unvaccinated per-

sons were tested daily by RT-PCR; antigen testing was not

used. On December 18, 2021, testing protocols transitioned

to symptom- or exposure-based testing, determined through

enhanced symptom screening and contact tracing for fully

vaccinated persons, resulting in approximately two thirds the

number of tests, but retaining a high level of case detection

(6). Around the same time, NFL also updated test-to-release

protocols (Box). Daily testing was requested for all fully vac-

cinated persons with COVID-19, who could be released from

isolation if they were asymptomatic or fever-free with symp-

toms improved for 24 hours with medical staff clearance, and

receipt of two negative or Ct≥35 RT-PCR test results (point of

care [POC] or laboratory-based) within 24 hours (2). Although

Ct values have not been validated as a measure of infectious-

ness (7), a conservative Ct cutoff was chosen by NFL based

on higher Ct values correlating with limited culturable virus

in other studies (8).

COVID-19 cases

identified during December 12,

2021–January 1, 2022, were stratified by whether persons

were fully vaccinated, partially vaccinated, or unvaccinated.

SARS-CoV-2 tests included either laboratory-based real-time

RT-PCR (BioReference Laboratories RT-PCR assay [Roche

Cobas assay], Roche) or POC RT-PCR (Mesa Biotech Accula

SARS-CoV-2 Test, Mesa Biotech Inc.); both tests demonstrated

A COVID-19 case was defined as detection of SARS-CoV-2 RNA using a

diagnostic nucleic acid amplification test performed by a Clinical Laboratory

Improvement Amendments–certified provider and confirmed by additional

RT-PCR tests alongside clinical adjudication. For COVID-19 cases, day of

diagnosis (“day zero”) was defined as the day of first positive test result, which

in this setting of high access to testing was often the day of symptom onset.

Morbidity and Mortality Weekly Report

300 MMWR / February 25, 2022 / Vol. 71 / No. 8 US Department of Health and Human Services/Centers for Disease Control and Prevention

BOX. Test-to-release from isolation procedures — National Football League, United States, June 16, 2021–January 1, 2022

June 16, 2021 (NFL season start)

• Requested daily laboratory-based and POC RT-PCR testing* for all fully vaccinated

†

persons with COVID-19

• Permitted fully vaccinated persons with COVID-19 to voluntarily return to work early (before 10 days since first

positive test) upon meeting the following testing and clinical criteria:

• Testing criteria

Two negative laboratory-based RT-PCR tests separated by ≥24 hours

One negative POC RT-PCR test before entry on the date of entry

• Clinical criteria

Asymptomatic for 48 hours

Medical clearance by the team physician

Review of test results by the NFL Chief Medical Officer and clinical consultants

• Upon return, all persons followed existing NFL-NFLPA masking and behavioral protocols

November 9, 2021

• Requested daily laboratory-based RT-PCR testing for all fully vaccinated persons with COVID-19

• Permitted fully vaccinated persons with COVID-19 to voluntarily return to work early (before 10 days since first

positive test) upon meeting the following testing and clinical criteria

• Testing criteria

Days 1–6 after a confirmed positive test result: two negative laboratory-based RT-PCR test results separated by ≥24 hours

Days 7–10 after a confirmed positive test result: 1) one negative laboratory-based RT-PCR test result; and 2) one

negative POC RT-PCR test result before entry on the day following specimen collection of initial laboratory-based

RT-PCR test (taken ≥24 hours later)

• Clinical criteria: Days 1–6 or Days 7–10

Asymptomatic for 48 hours (other than loss of taste or smell)

Medical clearance by the team physician

Confirmation of test results by the NFL Chief Medical Officer and clinical consultants

• Upon return, all persons followed existing NFL-NFLPA masking and behavioral protocols

See box footnotes on the next page.

previous high performance in this setting (3) (NFL, unpub-

lished data). Sequence analysis was performed using Illumina

COVIDSeq (9) for a portion of cases. Symptoms throughout

illness were clinically monitored but not centrally recorded;

NFL clubs requesting early return permission were required

to provide documentation of asymptomatic or improving

symptom status. Clubs were requested to closely monitor

persons returning and report any new symptoms; persons

returning were required to adhere to applicable NFL-NFLPA

masking policies.

This report describes results from the NFL test-to-release

from isolation strategy for fully vaccinated persons with

confirmed COVID-19 during December 14–19, 2021.

These dates reflect a period during which the Omicron vari-

ant accounted for 97% of sequenced viruses, and protocols

requested COVID-19 patients test daily for 10 days after

diagnosis (isolation ended on day 5 beginning December 28,

2021). Fully vaccinated persons were included if they were

tested ≥6 times during infection, with a final test on day 8 or 9

postdiagnosis or achieved two negative or Ct≥35 RT-PCR

test results (after which testing ceased). Subsequent transmis-

sion from persons returning from isolation early could not be

ascertained because of high community COVID-19 incidence

and limited Omicron genomic sequencing diversity. The

analysis in this report was conducted by IQVIA on behalf of

NFL with CDC’s support. This activity was reviewed by CDC

and was conducted consistent with applicable federal law and

CDC policy.

During December 12, 2021–January 1, 2022, a surge in

COVID-19 cases occurred among NFL players and staff, with

an average of 336 cases per week, compared with 30 cases per

week during the preceding 3 months. Sixty-six (53%) cases

occurred among 125 unvaccinated persons, three (23%)

45 C.F.R. part 46, 21 C.F.R. part 56; 42 U.S.C. Sect. 241(d); 5 U.S.C. Sect.

552a; 44 U.S.C. Sect. 3501 et seq.

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US Department of Health and Human Services/Centers for Disease Control and Prevention

December 16, 2021

• Strongly requested daily testing using laboratory-based and POC RT-PCR after a confirmed positive test result for all

fully vaccinated persons with COVID-19

• Permitted fully vaccinated persons with COVID-19 to voluntarily return to work early (before 10 days since first

positive test result) upon meeting the following testing and clinical criteria

• Testing criteria: two samples collected ≤24 hours of each other on Day 1 or thereafter (may be collected on the same day;

must be separate swabs)

Two negative or Ct≥35 laboratory-based RT-PCR test results; or

One negative or Ct≥35 laboratory-based RT-PCR test result and one negative POC RT-PCR test result; or

Two negative POC RT-PCR test results

• Clinical criteria

Asymptomatic or fever-free and improving symptoms for ≥24 hours

Medical clearance by the team physician

Confirmation of test results by the NFL Chief Medical Officer and clinical consultants

• Although Ct values are not a measure of infectiousness

a Ct cutoff of 35 was chosen based on higher Ct values

correlating with limited culturable virus using alternative RT-PCR tests**

• Upon return, all persons followed existing NFL-NFLPA masking and behavioral protocols

December 28, 2021

• Allowed for day 5 return if fever-free for ≥24 hours, asymptomatic or improving symptoms, and cleared by team

physician, regardless of vaccination status

††

• Once cleared from isolation (between Days 5 and 10), all persons were required to wear a KN95 or N95 mask at all

times other than when actively engaged in physical activity at practice or in a game until 10 days following positive test

result, at which time they returned to existing NFL-NFLPA masking protocols

• Fully vaccinated persons with COVID-19 could return before Day 5 by meeting the December 16 protocol criteria.

Upon return, persons were required to follow existing NFL-NFLPA masking and behavioral protocols.

Abbreviations: FDA = Food and Drug Administration; NFL = National Football League; NFLPA = National Football League Players Association; POC=point-

of-care; RT-PCR=reverse transcription–polymerase chain reaction.

* SARS-CoV-2 tests included either laboratory-based real-time RT-PCR (BioReference Laboratories RT-PCR assay [Roche Cobas assay], Roche) or POC RT-PCR

(Mesa Biotech Accula SARS-CoV-2 test, Mesa Biotech Inc.); the Roche Cobas RT-PCR test used received FDA Emergency Use Authorization as a qualitative

diagnostic assay with a Ct cutoff of >40. Use of this assay with alternative Ct cutoffs is not authorized by FDA. The Mesa Biotech Accula test produces only

a qualitative result (positive/negative) and no Ct values.

†

Fully vaccinated was defined as ≥14 days after primary vaccine series completion, with or without a booster. Under NFL-NFLPA protocols, persons with 1 dose

of a 2-dose mRNA vaccination series and a documented history of COVID-19 were subject to the same requirements as fully vaccinated persons in the NFL-

NFLPA protocols; however, these persons were excluded from analyses summarizing the test-to-release from isolation strategy.

https://www.nfl.com/news/nfl-updates-covid-19-protocols-to-allow-for-quicker-return-from-quarantine-for-v

https://www.cdc.gov/coronavirus/2019-ncov/lab/faqs.html

** https://academic.oup.com/cid/article/73/11/e3884/6018217

††

https://www.cdc.gov/media/releases/2021/s1227-isolation-quarantine-guidance.html

BOX. (Continued) Test -to-release from isolation procedures — National Football League, United States, June 16, 2021–January 1, 2022

among 13 partially vaccinated persons, and 924 (14%) among

6,443 fully vaccinated persons.** Among 117 (12%) cases

with a sequenced virus isolate during this period, 111 (95%)

were classified as Omicron and six (5%) as the SARS-CoV-2

B.1.617.2 (Delta) variant.

** The remaining 15 cases occurred among 75 persons with 1 dose of a 2-dose

mRNA vaccination series and a documented history of COVID-19, who were

subject to the same requirements as fully vaccinated persons in the NFL-

NFLPA protocols. These persons were not included in analyses summarizing

the test-to-release from isolation strategy.

Using data from December 14–19, 2021, a total of 218 (5%)

cases were identified in NFL players and staff members among

4,134 persons tested; 87 (97%) of 90 sequenced isolates were

Omicron. Among 201 COVID-19 cases in fully vaccinated

persons that were either confirmed as Omicron or unsequenced

(presumed Omicron), 173 (86%) tested for isolation release;

the remaining 28 (14%) did not test frequently enough for

inclusion. Among these 173 persons, 53 (31%) obtained at

least one negative or Ct≥35 RT-PCR test result on or before

day 5 postdiagnosis, 79 (46%) on or before day 6 (concluding

5 full days of isolation), and 146 (84%) within 10 days after

Morbidity and Mortality Weekly Report

302 MMWR / February 25, 2022 / Vol. 71 / No. 8 US Department of Health and Human Services/Centers for Disease Control and Prevention

diagnosis. Among the 146 persons with at least one negative

or Ct≥35 RT-PCR test result in the 10 days after diagnosis,

the median interval from diagnosis to first negative result was

6 days (IQR=5–8 days); among all 173 persons, the median

interval was 7 days (IQR=5–9 days) (Figure 1).

Overall, 130 (75%) of 173 persons tested for return from

isolation met NFL-NFLPA protocol testing criteria before

10 days, with median interval to second negative or Ct≥35

test result of 7 days (IQR = 5–8 days); 122 (71%) met both

testing and clinical criteria and were eligible to return to work

before 10 days after diagnosis (Figure 2). Among the 130 per-

sons who tested for early return from isolation, 116 applied

for early return; the remaining 14 did not because either their

job function did not require early return (six), or they were

still symptomatic (six); two did not apply for early return for

unknown reasons. Among 173 persons who tested for release

from isolation, the median time to return to work was 8 days

(IQR=6–10 days). None of the persons who returned to work

reported onset of new symptoms after early return during the

10 days after diagnosis.

Summary

What is already known about this topic?

On December 16, 2021, the National Football League (NFL)

updated its test-to-release from COVID-19 isolation protocols in

response to increasing COVID-19 cases and predominance of

the SARS-CoV-2 Omicron variant.

What is added by this report?

Among 173 vaccinated adults with COVID-19 undergoing

serial reverse transcription–polymerase chain reaction

(RT-PCR) testing during Omicron predominance, 46% received

a negative or high cycle threshold RT-PCR test result on or

before day 6 postdiagnosis.

What are the implications for public health practice?

Although a positive RT-PCR test result does not necessarily

indicate infectiousness, these data indicate that persons with

COVID-19 should continue to take precautions, including

correct and consistent mask use, for a full 10 days after

symptom onset or after initial positive test result if they

are asymptomatic.

FIGURE 1. Percentage of 173 fully vaccinated* COVID-19 patients (SARS-CoV-2 B.1.1.529 [Omicron] and unsequenced

†

) with a negative or

cycle-threshold ≥35

reverse transcription–polymerase chain reaction test result, by number of days after diagnosis — National Football

League, United States, December 14–19, 2021

100

0 1 2 3 4 5 6 7 8 9

Percentage with negative or Ct≥35 RT-PCR test result

No. of days after diagnosis

46% after

5 full days

Abbreviations: Ct = cycle threshold; NFL = National Football League; NFLPA = National Football League Players Association; RT-PCR = reverse transcription–polymerase

chain reaction.

* Fully vaccinated was defined as ≥14 days after primary vaccine series completion. Under NFL-NFLPA protocols, persons with 1 dose of a 2-dose mRNA vaccination

series and a documented history of COVID-19 were subject to the same requirements as fully vaccinated persons in the NFL-NFLPA protocols; however, these persons

were excluded from analyses summarizing the test-to-release from isolation strategy.

†

Among 173 cases, 77 (45%) were sequenced as Omicron, and 96 (55%) were not sequenced (unsequenced). During December 14–19, 2021, 87 (97%) of 90 sequenced

isolates from 218 total cases were Omicron, therefore unsequenced cases were presumed Omicron.

Although Ct values are not a measure of infectiousness (https://www.cdc.gov/coronavirus/2019-ncov/lab/faqs.html) a Ct cutoff of 35 was chosen by NFL based on

higher Ct values correlating with limited culturable virus using alternative RT-PCR tests (https://academic.oup.com/cid/article/73/11/e3884/6018217).

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Discussion

This report describes results from the NFL test-to-release

from isolation strategy for fully vaccinated NFL players and

staff members with COVID-19 during December 14–19,

2021, after emergence of the Omicron variant. Before day 10

postdiagnosis, ≥71% of infected persons were asymptomatic

or significantly improved for 24 hours and had received two

negative or Ct≥35 test results and were therefore eligible to

return to work under NFL-NFPLA protocols. Although

persons were not systematically tested after return from

isolation, and transmission after early return from isolation

could not be documented, none of the persons who returned

to work experienced new symptoms detected by in-facility

symptom monitoring.

CDC recommends an additional 5 days of mask use when

around others following an isolation period of 5 days, which

can end when a person has been fever-free for 24 hours and

other symptoms have improved (10). The results from this

analysis support this masking recommendation, although

infectiousness or transmission could not be assessed. Under

FIGURE 2. Test-to-release from isolation results among 201 fully vaccinated* COVID-19 patients (SARS-CoV-2 B.1.1.529 [Omicron] and

unsequenced

†

) undergoing serial reverse transcription–polymerase chain reaction testing

to allow release from isolation — National Football

League, December 14–19, 2021

¶,

,††

27 (16%)

No RT-PCR–negative or Ct≥35 test result

during 9-day testing period

146 (84%)

At least one RT-PCR–negative or Ct≥35 test

result within 10 days

173 (86%)

Tested approximately daily from initial positive test result until isolation end

(meeting criteria or 10 days post-diagnosis)

28 (14%)

Did not test frequently enough

201 cases among fully vaccinated National Football League players and sta members

Initial positive test results received December 14–19, 2021; conrmed or presumed Omicron

130 (89%)

Met NFL testing criteria for release

from isolation (two RT-PCR–negative or

Ct≥35 test results)

16 (11%)

One RT-PCR–negative or

Ct≥35 test result

Abbreviations: Ct = cycle threshold; NFL = National Football League; NFLPA = National Football League Players Association; POC = point of care; RT-PCR = reverse

transcription–polymerase chain reaction.

* Fully vaccinated was defined as ≥14 days after primary vaccine series completion, with or without a booster. Under NFL-NFLPA protocols, persons with 1 dose of

a 2-dose mRNA vaccination series and a documented history of COVID-19 were subject to the same requirements as fully vaccinated persons in the NFL-NFLPA

protocols; however, these persons were excluded from analyses summarizing the test-to-release from isolation strategy.

†

Among 201 cases, 79 (39%) were sequenced as Omicron, and 122 (61%) were not sequenced (unsequenced). During December 14–19, 2021, 87 (97%) of 90

sequenced isolates from 218 total cases were Omicron, therefore unsequenced cases were presumed Omicron.

RT-PCR tests included either laboratory-based real-time RT-PCR (Bioreference Labs RT-PCR assay [Roche Cobas assay], Roche) or POC RT-PCR (Mesa Biotech Accula

SARS-CoV-2 Test, Mesa Biotech Inc.).

Among those who did not test frequently enough, 26 (93%) had a job function that did not require regular attendance in facility or immediate return or were

travel-related.

** Among 130 persons who met testing criteria, 122 (94%) met testing and clinical criteria for release from isolation, six had continuing symptoms, and two did not

apply for early return for unknown reasons.

††

Although Ct values are not a measure of infectiousness (https://www.cdc.gov/coronavirus/2019-ncov/lab/faqs.html) a Ct cutoff of 35 was chosen by NFL based on

higher Ct values correlating with limited culturable virus using alternative RT-PCR tests (https://academic.oup.com/cid/article/73/11/e3884/6018217).

Morbidity and Mortality Weekly Report

304 MMWR / February 25, 2022 / Vol. 71 / No. 8 US Department of Health and Human Services/Centers for Disease Control and Prevention

NFL’s test-to-release from isolation strategy, approximately one

half of fully vaccinated persons with COVID-19 had negative

or Ct≥35 RT-PCR test results after 5 full days of isolation (i.e.,

on day 6), and 84% by day 10. CDC advises that persons with

access to tests might use an antigen test toward the end of the

5-day isolation period (10), because RT-PCR tests can continue

to return positive results with high Ct values intermittently

after an initial positive result (4). Ct values are not a validated

measure of infectiousness; however, the data from this study

indicate that persons can receive a positive test result after a

5-day isolation period. It is therefore important for persons

with COVID-19 to continue to wear masks correctly and

consistently for a full 10 days after symptom onset or after an

initial positive test result if they are asymptomatic (10).

The findings in this report are subject to at least six limita-

tions. First, these data are based on results from highly sensi-

tive RT-PCR tests, whereas CDC advises that persons with

access to rapid antigen tests might use these toward the end

of the 5-day isolation period (10). Second, because of high

community incidence of COVID-19 during this period and

limited Omicron genomic sequencing diversity, subsequent

transmission postisolation release cannot be ascertained. Third,

this investigation is limited to a population of predominantly

adult men in an occupational setting, who are likely healthier

than the general population, and the NFL testing program

differed from U.S. community-based testing; thus, these find-

ings might not be generalizable to other populations. Fourth,

Ct values from RT-PCR tests do not necessarily indicate viral

load or infectiousness in an individual person, and other fac-

tors, including specimen collection and handling, can affect Ct

values (7). The use of a Ct≥35 cutoff-point for these RT-PCR

tests did not have Emergency Use Authorization and was not

systematically evaluated nor had either assay been evaluated

against the Omicron variant. Fifth, because of rapid administra-

tion of booster vaccine doses during the investigation period,

cases could not be reported by booster dose receipt status.

Finally, symptom data were not available throughout illness;

reporting of asymptomatic status on negative test receipt was

based on NFL clubs’ submission for early return permission.

In this report describing test-to-release from isolation

strategies in an occupational sport setting and RT-PCR test

results among fully vaccinated persons with Omicron variant

COVID-19, approximately one half had a negative result

or a Ct value ≥35 on or before day 6, concluding 5 days of

isolation. Although a positive RT-PCR test result does not

necessarily indicate infectiousness, these data indicate that

persons with COVID-19 should continue taking precautions,

including correct and consistent mask use, for a full 10 days

after symptom onset or after initial positive test result if they

are asymptomatic.

Acknowledgments

Monita Patel, CDC; National Football League (NFL) club

infection control officers; NFL team athletic trainers, physicians, and

orthopedists; NFL Players Association; NFL COVID-19 Advisory

and Operational Team including Dawn Aponte, NFL; Michele

Best, University of Maryland Capital Region Health; Meghan C.

Carroll, NFL; M. Anthony Casolaro, Washington Football Team;

Molly Delaney, NFL; Daniel Eichner, Sports Medicine Research and

Testing Laboratory; Jacob Frank, NFL; John Lynch, Department of

Medicine, University of Washington; Jimmie Mancell, Department

of Medicine, University of Tennessee Health Science Center; Damion

Martins, Atlantic Sports Health, Morristown Medical Center; John

Mellody, NFL; Eric Sugarman, Minnesota Vikings; IQVIA and NFL

contact tracing and technical team including Megan Miraval, Ally

Thrasher, Sabrina Trujillo Smith, Madeline Lassiter, Emily Watson,

Kristin Archibald, Emma Bergqvist, Paul Blalock, Justin Reid, Julie

Griffith, Kristina Zeidler; Sequencing partners at Tempus and Yale

School of Public Health.

Corresponding author: Christina D. Mack, Christina.M[email protected].

IQVIA Real-World Solutions, Durham, North Carolina;

CDC COVID-19

Emergency Response Team;

Infection Control Education for Major Sports,

LLC, Chapel Hill, North Carolina;

Williamson Medical Center, Franklin,

Tennessee;

National Football League, New York, New York;

Louisiana State

University Health Sciences Center, Baton Rouge, Louisiana;

Eden Medical

Center, Castro Valley, California;

National Football League Players Association,

Washington, D.C.

All authors have completed and submitted the International

Committee of Medical Journal Editors form for disclosure of

potential conflicts of interest. Christina D. Mack, Erin B. Wasserman,

and Saamir Pasha report full-time employment by IQVIA. Deverick J.

Anderson reports receipt of royalties for authorship from UpToDate

Online, LLC and co-ownership of Infection Control Education

for Major Sports, LLC. Patti Walton reports consulting fees from

NFL, honoraria for presentation from Ortho Clinical Diagnostics,

payment as an expert witness regarding laboratory practices, support

for travel to meetings from the American Society for Clinical

Pathology (ASCP), serving on the Board of Directors of the Clinical

Laboratory Management Association (2019–2021), membership on

the ASCP Board of Governors (2019–current), and Chairmanship

of the Tennessee Medical Laboratory Licensing Board (2019–2021).

Catherine O’Neal reports consulting fees from NFL. Christopher J.

Hostler reports co-ownership of Infection Control Education for

Major Sports, LLC. Allen Sills and Emily Myers report employment

by NFL. Navdeep Singh reports receipt of consulting fees from NFL

and the Las Vegas Raiders. No other potential conflicts of interest

were disclosed.

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References

1. CDC. Variant proportions. Atlanta, GA: US Department of

Health and Human Services, CDC; 2021. https://covid.cdc.gov/

covid-data-tracker/#variant-proportions

2. National Football League. NFL updates COVID-19 protocols to allow

for quicker return from quarantine for vaccinated individuals. New York,

NY: National Football League, 2021. https://www.nfl.com/news/

nfl-updates-covid-19-protocols-to-allow-for-quicker-return-from-

quarantine-for-v

3. Mack CD, Osterholm M, Wasserman EB, et al. Optimizing SARS-CoV-2

surveillance in the United States: insights from the National Football

League Occupational Health Program. Ann Intern Med 2021;174:1081–9.

PMID:34125571 https://doi.org/10.7326/M21-0319

4. Mack CD, DiFiori JD, Tai C, et al. SARS-CoV-2 transmission risk

among National Basketball Association players, staff, and vendors

exposed to individuals with positive test results after COVID-19 recovery

during the 2020 regular and postseason. JAMA Intern Med

2021;181(7):960–66. PMID:33885715 https://doi.org/10.1001/

jamainternmed.2021.2114

5. CDC. For NFL players, leadership and teamwork builds COVID-19

vaccine confidence. Atlanta, GA: US Department of Health and Human

Services, CDC; November 12, 2021. https://www.cdc.gov/vaccines/

covid-19/health-departments/features/NFL.html

6. National Football League. New COVID-19 protocols to feature targeted

testing of fully vaccinated players, staff. New York, NY: National Football

League, 2021. https://www.nfl.com/news/new-covid-19-protocol-to-

feature-targeted-testing-of-fully-vaccinated-players-st

7. CDC. Frequently asked questions about Coronavirus (COVID-19) for

laboratories. Atlanta, GA: US Department of Health and Human

Services, CDC; November 12, 2021. https://www.cdc.gov/

coronavirus/2019-ncov/lab/faqs.html

8. Jefferson T, Spencer EA, Brassey J, Heneghan C. Viral cultures for

Coronavirus disease 2019 infectivity assessment: a systematic review.

Clin Infect Dis 2021;73:e3884–99. PMID:33270107 https://doi.

org/10.1093/cid/ciaa1764

9. Vogels CBF, Breban MI, Ott IM, et al. Brazil-UK CADDE Genomic

Network; Network for Genomic Surveillance in South Africa. Multiplex

qPCR discriminates variants of concern to enhance global surveillance

of SARS-CoV-2. PLoS Biol 2021;19:e3001236. PMID:33961632

https://doi.org/10.1371/journal.pbio.3001236

10. CDC. Quarantine and isolation. Atlanta, GA: US Department of Health

and Human Services, CDC; January 27, 2022. https://www.cdc.gov/

coronavirus/2019-ncov/your-health/quarantine-isolation.html