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The Houston Astros placed five players, including four starting position players, on the injured list Wednesday. Infielders Jose Altuve and Alex Bregman, catcher Martin Maldonado, and designated hitter Yordan Alvarez were all placed on the injured list for undisclosed reasons, the team announced. Utility infielder Robel Garcia joined them.

During a conference call with reporters, Astros GM James Click confirmed the five players were placed on the injured list "as a result of health and safety protocols," according to the Houston Chronicle's Chandler Rome. Click said the Astros became aware of the situation following Tuesday's game, and Altuve's curious ninth inning removal is unrelated.

Being placed on the COVID-19 list does not necessarily mean the players have tested positive. They could have come into close contact with a person who tested positive, or broke the league's health and safety protocols (eating indoors at a restaurant, etc.). The COVID-19 list has no minimum or maximum stay, though players who test positive must isolate for 10 days.

Astros manager Dusty Baker told reporters "all the guys involved had at least their first (vaccination) shots," according to Rome. The Astros stopped in Houston after spring training to receive vaccinations on their way to Oakland for Opening Day. It's unknown whether the club exceeded the 85 percent threshold for relaxed protocols.

Alvarez missed the start of last season after testing positive for COVID-19. He told reporters he tested positive in July, right before summer camp, and that his only symptoms were mild headaches. Alvarez returned in mid August and hit a home run in his first at-bat

Catcher Garrett Stubbs, outfielder Ronnie Dawson, and infielders Taylor Jones, Abraham Toro, and Alex De Goti were called up to fill the vacant roster spots. De Goti and Dawson have never played in MLB.

The Chicago Cubs recently placed three relievers on the COVID-19 list after bullpen coach Chris Young and first base coach Craig Driver tested positive for the virus.

The Astros started the season 6-1 but have since lost four straight, including the last two to the Tigers.