Per Matt Barrows of The Athletic, seven 49ers are now on the list. The other four players are defensive linemen Arik Armstead and Javon Kinlaw, center Hroniss Grasu and linebacker Joe Walker.
Aiyuk and Williams have been on the list twice. Placement there either means that a player has tested positive for COVID-19 or has come in close contact with someone who has.
It is unknown which category the players fall under.
"Clubs are not permitted to comment on player's medical status other than referring to roster status and may not disclose whether the player is in quarantine or is positive for COVID-19," the team wrote in a press release earlier this week.
As ESPN's Jake Trotter noted, "a player who tests positive for COVID-19 can't return to the team until at least 10 days after the start of symptoms, plus at least 24 hours after symptoms have passed."
If players are deemed high-risk close contacts, then the protocol is as follows, per NFL.com: "Such player will remain on that list until at least five days have passed since the date on which the player was last in contact with the infected individual. The player will be permitted to resume club activities on the sixth day after such last exposure if all his PCR tests, including the fifth testing day, are negative."
The 49ers are entering their bye week and don't play again until the Nov. 29 road game against the Los Angeles Rams.
If Aiyuk, Williams or Helm tested positive, then they should miss that game. They would have a chance to return in time if they were close contacts, however.
Aiyuk, who was the 25th overall pick in the 2020 NFL draft, is second on the team with 35 catches for 446 receiving yards. He's also added five total touchdowns and 61 rushing yards.
Williams has started all nine of his games for the 49ers at left tackle. San Francisco acquired the seven-time Pro Bowler from the Washington Football Team on April 25.
Helm, a former 49ers practice-squad player who was on his third stint on the team's active roster, has played in three games this year, with all of his snaps coming on special teams.