The Yankees’ post-All-Star break opener against the Boston Red Sox on Thursday night was postponed because of positive COVID-19 tests among vaccinated New York pitchers Jonathan Loaisiga, Nestor Cortes Jr. and Wandy Peralta.

“It’s a fluid situation that could spread. It has spread to some degree,” Yankees general manager Brian Cashman said. “We have three positives and we have three pending that we’ve had rapid tests on. … We’ll wait now for the lab tests to come back, which I’m assuming is going to be positive, as well. So that would increase our number to six, but we’re not at six yet. We’re at three confirmed.”

Loaisiga went on the COVID-19 injured list Saturday, when the Yankees were in Houston, and he did not travel home with the team Sunday. Cortes and Peralta went on the COVID-19 IL on Thursday.

Cashman said all three were fully vaccinated, as are most of the players on the team. Among the three, two received the Johnson & Johnson vaccine, and the other was either Pfizer or Moderna, according to Cashman.

“Those players are doing well thus far,” he said. “And that would speak again to the belief that those vaccinations are working and ultimately they’re to protect us from severe illness and/or death.”

The three players awaiting lab results are in quarantine. Cashman would not say whether they include the Yankees’ All-Stars who were in Denver: Aaron Judge, Gerrit Cole and Aroldis Chapman.

MLB was conducting contact tracing under its protocols.

“The vaccines that we encourage everybody to get guarantee not getting hospitalized and not getting death coming from COVID, which is important, but it doesn’t prevent you from contracting COVID,” Cashman said. “It just obviously protects you from the severe worst-case scenario effects from COVID.”

Cashman said Major League Baseball had not yet decided whether to postpone Friday’s second scheduled game of the four-game series.

“The last year, year and a half, has kind of in some ways kind of prepared you for this kind of stuff,” Yankees manager Aaron Boone said. “Certainly disappointing and frustrating.”

This was the eighth COVID-related postponement this season but the first in nearly three months. Also put off were a three-game series that had the New York Mets at Washington from April 1-4, and Atlanta’s game at the Nationals on April 5, two Minnesota at Los Angeles Angels games on April 17-18 and a Twins at Oakland game on April 19.

There were 45 regular-season games postponed for virus-related reasons during last year’s pandemic-shortened season but just two were not made up, between St. Louis and Detroit.

New York, fourth in the AL East at a disappointing 46-43, was among the first MLB teams to reach the 85% vaccination threshold that triggers a lessening of coronavirus protocols such as dropping mask use in dugouts and bullpens.

MLB said in its last announcement June 25 that 23 of it 30 teams had reached 85% vaccinations among tier 1 individuals such as players and on-field staff. The Red Sox were not among them.

Despite all those vaccinations, the Yankees had more than a half-dozen positive COVID tests in May involving staff, including pitching coach Matt Blake, third base coach Phil Nevin and first base coach Reggie Willits. Nevin, despite being vaccinated, became seriously ill with a kidney infection that kept him away from the team for more than three weeks.

No Yankees players tested positive then, though shortstop Gleyber Torres had a false positive, according to Boone.

New York players were on the field taking early batting practice about 3 1/2 hours before the scheduled start Thursday when the Yankees asked media to leave the field while the team conducted COVID testing.

Boston, whose 55-36 record matched Houston for best in the AL, came onto the field as the postponment was announced, then took batting practice until 6 p.m.

MOVING UP

Red Sox: Boston is bringing up OF Jarren Duran and RHP Tanner Houck. Duran, a 24-year-old who hit .368 for the U.S. in Olympic qualifying, was in the lineup for a major league debut, playing center and batting seventh. Houck, who pitched in three game for the Red Sox in April, will be in the bullpen at first and likely will start Wednesday against Toronto in Buffalo. Duran hit .270 with 15 homers and 32 RBIs in 189 at-bats at Triple-A Worcester. Coach Bruce Crabbe called him into coach Billy McMillon’s office after Wednesday’s game. “They opened up a spot on the Olympic roster for you,” Duran recalled Crabbe saying. “I was like: `Oh, awesome, cool.′ And then he goes: ‘Oh, but you could actually go to the big leagues if you want to do that. That could be a side job for you.’” His mother, father, brother, girlfriend and two uncles were in New York for his debut.

Yankees: OF Trey Amburgey’s contract was selected from Triple-A Scranton/Wilkes-Barre. The 26-year-old right-handed hitter was batting .312 with seven homers and 35 RBIs in 141 at-bats. C Rob Brantly and INF Hoy Jun Park were scratched from the RailRiders’ lineup Thursday night, a sign they may join the Yankees on Friday.

NUMBERS GAME

New York 2B Rougned Odor has switched to No. 12 from No. 18.

TRAINER’S ROOM

Red Sox: LHP Chris Sale pitched in a game for the first time since Tommy John surgery on March 30, 2020, throwing 39 pitches over three scoreless innings for the FCL Red Sox at the FCL Orioles Orange. The 32-year-old left-hander allowed four hits and struck out five. Sale threw at up to 97 mph, according to manager Alex Cora, and likely will start Tuesday for Double-A Portland.

Yankees: LHP Zack Britton was activated from the injured list after recovering from a strained left hamstring that had sidelined him since June 25.

(AP)