The NFL is requiring players, coaches and other team personnel to receive a COVID-19 booster by Dec. 27.

In a memo sent to teams on Monday and obtained by The Associated Press, the league said: "Given the increased prevalence of the virus in our communities, our experts have recommended that we implement the CDC’s recommendation."

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The league’s requirement extends to all Tier 1 and Tier 2 individuals who have previously received the vaccine. The CDC recommends an individual who received a second Pfizer or Moderna shot to complete the primary vaccine series more than six months earlier should receive a booster shot. An individual that received the Johnson and Johnson shot more than two months earlier should receive a booster shot.

The following do not have to meet the requirement:

— An individual who is not eligible for a booster pursuant to the CDC definition.

— An individual who is in the 90-day test holiday after a confirmed positive COVID-19 test under the league protocols.

— An individual who received monoclonal antibodies within the immediately preceding 90 days.

— An individual whose "S" antibody level on an antibody test administered via BRL (BioReference Lab) at the club facility is 2500 or greater.

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The league says any individual who is not currently subject to the requirement for boosters will be required to obtain the booster within 14 days of becoming eligible.

Teams were asked to provide booster shots to all eligible tiered staff as soon as possible, and to consider making booster shots available for player and staff families and cohabitants.

A season-high total of 36 players were placed on the COVID-19/reserve list Monday.