A new memo released by the league that stressed the importance of receiving booster shots was obtained by the Associated Press. It told players and staff that the shots should be received “as soon as possible, particularly in light of the current coronavirus situation and increasing cases.” This is the second notice sent by the NBA this week to players and staff encouraging getting booster shots.

The notices come as COVID-19 cases are increasing across the country. The increases are especially being reported in areas where NBA teams are located. The league has seen an increase in cases reported by players, team staff and their family members. Although a vaccine mandate is not implemented across the league, 97 percent of NBA players are vaccinated, including members that have been testing positive for coronavirus.

At least eight players are currently seeking treatment in line with the league’s health and safety protocols. One player who had been treated for the virus, Tobias Harris of the Philadelphia 76ers, returned to the court on November 11 for his first game after testing positive.

“I’m working my way back into it,” Harris told reporters.

For more reporting from the Associated Press, see below.

The memo told players and coaches that it is no longer advisable to wait before receiving the additional dose.

Earlier in the week, the NBA and the National Basketball Players Association said they were recommending the booster shots be received by those who are fully vaccinated, suggesting that it get done by December 1 in most cases.

Other NBA players currently known to be in the league’s protocol include Philadelphia’s Joel Embiid, Matisse Thybulle and Isaiah Joe, San Antonio’s Jakob Poeltl and Jock Lansdale, Cleveland’s Kevin Love and Lauri Markkanen, and Chicago’s Nikola Vucevic.

People who are fully vaccinated are still strongly protected against hospitalization and death from COVID-19. But immunity against infection can wane over time, and the extra-contagious Delta variant is spreading widely. The NBA—following the lead of U.S. health authorities—want to shore up protection in at-risk people who were vaccinated months ago.

The guidance from the league earlier in the week made clear that those who received the single-dose Johnson & Johnson vaccine more than two months ago should prioritize getting a Pfizer or Moderna booster quickly. Those who received the Pfizer or Moderna vaccine more than six months ago were also told earlier in the week to seek boosters.

The most notable holdout for the NBA’s vaccination rate is Brooklyn’s Kyrie Irving, a perennial All-Star who is not being allowed by the Nets to play until he gets vaccinated.