The Mariners didn't identify who tested positive for the coronavirus. Those placed on the IL were Robert Dugger, Will Vest, Drew Steckenrider and Anthony Misiewicz.
"The No. 1 priority obviously is the health and safety of our players and everybody understanding the importance of getting vaccinated," Mariners manager Scott Servais told reporters before the opener of a three-game series against the San Diego Padres.
"But it is an individual choice and unfortunately not all of our guys are vaccinated, so it's something we have to deal with like other teams have had to deal with throughout Major League Baseball. It's real, it's out there, it is affecting our roster and we'll try to deal with it as best we can."
In corresponding roster moves, the Mariners recalled left-hander Aaron Fletcher and right-handers Wyatt Mills and Yohan Ramirez from Triple-A Tacoma. Seattle also selected the contract of infielder Eric Campbell from Triple-A.
Also Friday, the Mariners activated right-handed pitcher Keynan Middleton from the 10-day injured list. He had missed time because of a strained right biceps.
Entering Friday, Seattle (21-23) sat third in the American League West. The Mariners trail the division-leading Houston Astros by five games.
This week in Major League Baseball