MMWR - NFL Study on When to Be Released if COVID(+) Save

MMWR has reported the results of the National Football Leagues (NFL) change in SARS-CoV-2 testing program that went into effect in December 2021, at the height of the Omicron variant surge, showing that among those with asymptomatic infection, only half were PCR test negative and could return to work.

The test cohort included 173 fully vaccinated adults with confirmed (test positive) COVID-19 between December 14–19, 2021. By day 6, 46% had negative test results and 84% were negative by day 10.

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; 122 (71%) met both testing and clinical criteria and were eligible to return to work before 10 days after diagnosis. 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.

Thus the proportion of persons with positive test results decreased with time, with approximately one half remaining positive RT-PCR test results after 5 days of isolation. While being test positive at day 5 does not necessarily mean these persons are infectious (RT-PCR tests might continue to return positive results long after an initial positive result), these findings 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 initial positive test result if they are asymptomatic. 

The 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. The results from this analysis support this masking recommendation, although infectiousness or transmission could not be assessed.

The NFL requires vaccination and boosters in those who deal with players and strongly advises but does not mandate, vaccination amongst the players. As of October 13, 2021, the NFL population vaccination rate was >96% (staff members >99%; players >94%). For most of the 2021 season, fully vaccinated persons were tested weekly and unvaccinated persons were tested daily by RT-PCR (antigen testing was not used).

In December 2021, the protocol changed, with the NFL transitioning 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.

For vaccinated persons who were test positive (asymptomatic), daily testing was resumed and isolation was lifted if they were asymptomatic or fever-free with symptoms 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.

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%) 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.