Fernando Tatis Jr. and Yankees Coach Test Positive for Coronavirus

Even as the number of coronavirus vaccinations among Major League Baseball personnel slowly ticked upward, two teams announced on Tuesday that they were dealing with new virus cases. One was a rare breakthrough case, in which a person tested positive despite being fully vaccinated.

Fernando Tatis Jr., San Diego’s superstar shortstop, tested positive and was asymptomatic, Padres Manager Jayce Tingler told reporters on Tuesday ahead of the team’s game in Colorado. As a result, Tatis was placed on the injured list, and so were two teammates who have been in close contact with him, Jorge Mateo and Jurickson Profar.

In St. Petersburg, Fla., ahead of a game against the Tampa Bay Rays, the Yankees announced that third base coach Phil Nevin, who was fully vaccinated, had tested positive and was in isolation in Tampa. “He’s doing OK,” Yankees Manager Aaron Boone said.

Boone said that Nevin’s positive test emerged on Sunday, when the team flew to Tampa after playing in New York, and that the Yankees had been undergoing a range of virus tests, from polymerase chain reaction to rapid, over the past 24 to 36 hours. If not for the Yankees’ high vaccination rate, Boone said, the team’s situation would have been handled differently.

According to the Centers for Disease Control and Prevention, breakthrough cases are expected despite the effectiveness of vaccines.

“No vaccines are 100 percent effective at preventing illness,” the C.D.C.’s website said. “There will be a small percentage of people who are fully vaccinated who still get sick, are hospitalized, or die from Covid-19.”

Some news media reports indicated that there had been multiple positive tests among the Yankees coaching staff, but Boone said the test results for a few other coaches and staff members were still pending. He also said that people who weren’t necessarily close contacts of Nevin’s but who fell into a gray area had been sent home out of an abundance of caution.

No players were affected, but Boone said the Yankees were operating with “a bit of a skeleton staff.”

Boone said that Carlos Mendoza, the team’s bench coach, had been asked to cover Nevin’s duties at third base, and that Mario Garza, who works in the Yankees’ minor league system, had been brought up to the major leagues to coach first base in place of Reggie Willits.

Although Boone declined to detail all of the Yankees’ absences, the bullpen coach, Mike Harkey, made a visit to the mound during the game instead of the pitching coach, Matt Blake.

Nevin’s case was the first for the Yankees during the 2020 and 2021 regular seasons; they also had none in the postseason last year. A few players, like closer Aroldis Chapman, infielder D.J. LeMahieu and relievers Luis Cessa and Zack Britton, tested positive in the off-season or during the lead-up to the 2020 regular season.

“We’ve all learned that playing through a pandemic and going back to last year, nothing kind of surprises you,” Boone said. “But still, it does catch you off guard a little bit when you do get that news.”

Gerrit Cole, the Yankees’ star pitcher and a top players’ union official, said that the team had met as a whole and heard from doctors and that everyone was OK with playing on Tuesday. Cole, who had returned to wearing a mask during his video interview with reporters on Tuesday, said the team was being tested “like crazy” — at least twice a day.

“As a whole, we’re looking to press on,” he said. “Different levels of comfortability across the club, so we’re just trying accommodate that and stick together as a group, and make sure everybody is in a good spot to perform tonight, which we felt confident as a group that we could do.”

The rewards included, among other things, masks no longer being required in the dugout or bullpen, indoor dining being permitted and visitors being allowed at the team hotel. Boone and Nevin, 50, received the single-dose Johnson & Johnson vaccine during spring training, and the Yankees offered a vaccine en masse to their players and staff last month. Still, Boone said on Tuesday that he would return to wearing a mask during the game.

M.L.B. and the players’ union said last week that more than 83 percent of all players and key staff members were considered partially or fully vaccinated. They also said that five of the 30 teams had already reached the threshold for loosened virus rules, and that seven others would join them once they reached the two-week mark to be considered fully vaccinated.

Boone said he hoped that Nevin’s case would not deter people from being vaccinated.

“The fact that we’re vaccinated in pretty large mass hopefully is something that will blunt this and allow a number of us to not get anything and keep the symptoms at a minimum if it does get through,” he said.