NEW YORK, Dec 16 (Reuters) - The National Football League (NFL) updated its COVID-19 protocols on Thursday amid a surge of new cases, requiring masks regardless of vaccination status, eliminating in-person meals and barring outside visitors while teams are traveling. The league has not canceled any games but saw close to 100 positive tests among players this week by Wednesday evening, as other North American sports leagues including the NHL and NBA scrambled to control outbreaks and keep their seasons on track. read more A memo from the NFL to all 32 clubs obtained by Reuters indicated the changes would remain in effect through Week 15 as the league works with the NFL Players Association (NFLPA) on further modifications. In the document, the league provided a pathway for vaccinated and asymptomatic players and staff to "test out" of quarantine after a positive, a move that could help avoid postponements as at least 22 clubs were affected by the rash of positive tests this week. "The changes we are making today aim to address the increase in cases and the advent of the Omicron variant," the NFL said in a written statement released Thursday, adding that it was encouraging booster shots "as the most effective protection." Players in the NFL have not been required to receive the COVID-19 vaccine. Earlier this week, the league ordered staff members to receive the booster by Dec. 27. read more "Based on expert advice, we will adjust the return-to-participation requirements for those who have recovered from COVID-19," the league said. "All of these changes are grounded in our data and science-backed approach."