The N.F.L. and the N.F.L. Players Association on Tuesday night amended this season’s Covid-19 protocols to mirror new guidance from the Centers for Disease Control and Prevention, halving the amount of time players who test positive for the coronavirus need to isolate regardless of their vaccination status.In a memo sent to all 32 of the league’s teams, Commissioner Roger Goodell said players infected with the coronavirus — whether vaccinated or unvaccinated — now need to quarantine for only five days, not 10, if their symptoms improve, after the C.D.C. revised its recommendation on Monday. Factors listed in the memo include whether the player’s fever subsided after 24 hours without medication, if their cough improved, and if team and league medical officials determine the player can return to the facility.The new protocols have drastic implications for the N.F.L., which has struggled to contain a surge of coronavirus cases as the playoffs approach. More than 94 percent of the N.F.L.’s players are vaccinated.Vaccinated players could clear protocols if they had two negative tests 24 hours apart, but positive tests for unvaccinated players normally led to their missing at least one game under previous rules, and the revised guidelines allow for them to potentially return to the field more quickly.The amendments follow a string of changes that the N.F.L. implemented this month regarding Covid-19 requirements. After previously testing vaccinated players weekly, the league and the players’ union agreed nearly two weeks ago to test them only when they are considered close contacts or show symptoms. It also mandated that essential staff who interact with players receive booster shots. Asymptomatic vaccinated players can also “test out” of protocols and return to play as soon as 24 hours after a positive test if they are no longer deemed contagious.But Tuesday’s memo is the first modification of protocols for the unvaccinated, who all season have been subject to stiffer requirements than their inoculated teammates. They are tested daily and must take separate planes to away games, among other things.The changes come after more than 90 players tested positive for the coronavirus on Monday, nearly one week after the N.F.L. rescheduled three games because of virus outbreaks fueled by the Omicron variant. The United States is averaging over 240,000 cases per day, and the memo recommended that all players and staff avoid social gatherings, bars and restaurants.In the last off-season, the N.F.L. mandated vaccinations for coaches and essential personnel, saying those who refused would be unable to interact with players. The league stopped short of requiring vaccinations for players, but strongly incentivized it by subjecting players who were not inoculated to stricter protocols.