Through 189 games over two seasons, the Red Sox walked through fire without getting burned. They got through the entire 2020 campaign and nearly five months this season without a single player testing positive for COVID-19 while with the team.
Then, on Aug. 27, the dam broke. A positive test for outfielder Kiké Hernández became the first reported case in what became an ongoing, season-endangering chain reaction.
Over the past three weeks, a dozen Red Sox players — including All-Stars Xander Bogaerts, Chris Sale, and Matt Barnes — and two members of the team’s support staff have tested positive. One additional player and one coach were placed in quarantine because they were unvaccinated and had close contact with teammates who tested positive.
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How did a bubble of good fortune get not merely punctured but shattered? Why has the Red Sox outbreak — which has necessitated a constant roster shuffle that left the team limping through the final weeks of a push toward the postseason — proven so difficult to contain?
Interviews with more than a dozen players, coaches, and Red Sox and league officials have offered approximations of reasons: more lenient testing protocols introduced at a time when the pandemic was waning; a portion of the team that did not embrace vaccination (it has not reached the 85 percent vaccinated mark); and a determination by Major League Baseball to move forward with a full game schedule in the face of a growing list of infections.
In retrospect, it is remarkable that the virus didn’t beset the Red Sox clubhouse through four-plus months of the season. Several opponents — the Twins in April, the Phillies and Yankees in July, the Rangers in August — experienced outbreaks while playing against the Red Sox.
Relief was the prevailing feeling on the team. Could their luck hold?
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The answer came in early August: No.
During a short trip from Detroit to Toronto, all Red Sox personnel in the traveling party were required by the Canadian government to be tested for COVID-19.

Bench coach Will Venable, who had been vaccinated, tested positive with an asymptomatic breakthrough infection. While no one else tested positive, first base coach Tom Goodwin — who is unvaccinated — had to quarantine in Canada for 10 days.
In the wake of Venable’s positive test, and amid the heightened protocols in place in Canada, the Red Sox significantly ramped up their testing and spent several days masking not just in the clubhouse but also in the dugout. At least temporarily, those around the team witnessed more careful behavior by players and other team personnel.
“My positive, I think, was sobering for the whole group,” said Venable.
A warning had been sounded.
The Hernández case
On Aug. 26, during a game against the Twins that concluded a six-game homestand, Hernández experienced body aches but didn’t consider them alarming.
After all, fatigue or dehydration seemed unsurprising given the humid nights in Boston, long games during the homestand, the late stage of the season, and a year in which Hernández’s everyday leadoff role had already yielded a career high in plate appearances.

With the Sox set to start a seven-game trip to Cleveland and Tampa Bay, Hernández, who is vaccinated, boarded the team bus for the airport around midnight and sat among his teammates for the short flight to Cleveland.
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Earlier in the season, Hernández might not have left Fenway Park. From April through mid-June, when MLB protocols specified that unvaccinated players would be tested every other day and fully vaccinated players would test at least twice a week, the Red Sox medical team tested everyone in a traveling party before every flight.
“The testing before each flight wasn’t a league thing; that was the Red Sox going above and beyond,” said Barnes, who is vaccinated and is also the Red Sox’ union representative.
That changed on June 16. At a time when infection rates throughout the US had crashed following the broad distribution of vaccines, a memo outlined the new testing protocols to which MLB and the Players Association had agreed, based on CDC guidance about fully vaccinated individuals.
Fully vaccinated individuals would no longer have to test unless they exhibited symptoms or had a known exposure to someone who tested positive. Masks would no longer be required indoors — in the clubhouse, for instance — for fully vaccinated players.

The memo noted in bold that it was necessary for all individuals to remain “hyper vigilant of their symptom status.” But Hernández simply hadn’t recognized his fatigue as a potential COVID symptom.
So with the Sox having stopped pre-flight testing for vaccinated players, Hernández wasn’t tested in Boston prior to the flight to Cleveland. When the plane landed around 3 a.m., members of the Sox wouldn’t have imagined anything was wrong.
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“He was chirping and he was all fired up,” said hitting coach Tim Hyers. “He was doing his Kiké stuff, bouncing off the walls while he was grabbing his luggage.”
The next morning, however, Hernández woke up with congestion and worsening body aches. His concern was immediate. He informed the team, and around 10 a.m., he took a rapid test that came back positive.
“I guess you can call me Patient Zero on the team,” Hernández said. “Whether I was the first one or not, I was the first one that actually tested positive.”
‘I guess you can call me Patient Zero on the team. Whether I was the first one or not, I was the first one that actually tested positive.’
Kiké Hernández
Charting the spread
The positive test set in motion a series of protocols for his teammates to follow, starting with contact tracing to determine who needed to be tested.
Not everyone on a team is immediately tested in case of a positive test. Every Tier 1 MLB employee — a 100-person group made up of the players and coaching staff with the Red Sox and Triple A Worcester, as well as select front office members who interact regularly with clubhouse personnel — is required to carry a Kinexon chip. The white rectangular sensor records “close contact” with others, meaning 15 minutes within 6 feet of someone who tests positive.
Based on both Kinexon data and interviews (necessary because there are times when Tier 1 individuals might not be carrying their chip), MLB requires any unvaccinated close contacts to enter a seven-day quarantine. Vaccinated close contacts are subjected to heightened testing but are not immediately quarantined.
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On the same day Hernández was placed on the COVID IL, second baseman Christian Arroyo began a close-contact quarantine — the protocol for unvaccinated Tier 1 individuals. But on that Friday and Saturday in Cleveland, there were no additional positive tests. The Sox held their breath, hoping that Hernández might be the only person to test positive.

It proved a false hope. On Sunday morning, Arroyo tested positive. So did strength and conditioning coach Kiyoshi Momose — a red flag, given that he works closely with virtually every player.
“I’m like, ‘[expletive], now I’ve definitely been exposed to it. It’s only a matter of time before I test positive,’ ” Barnes said.
Now, the Sox had to confront the question of how many other players might become infected.
“How long are the tentacles of this and where else is it going to extend?” wondered assistant general manager Eddie Romero, who was with the team in Cleveland.
That final day in Cleveland became uncomfortable. With a flight to Tampa Bay looming, the entire traveling party — not just individuals defined as close contacts — was tested. But weather concerns delayed the start of the afternoon game by 3 hours and 10 minutes, bringing the players together in the clubhouse.
“Not everybody has [a mask] on, just to be frank,” said Barnes. “Everybody’s sitting around or hanging out with guys or talking, playing cards, doing whatever. That three-hour delay might have just been a breeding ground for [COVID].”

The Sox blew an eighth-inning lead and lost, then bused to the airport for a flight to Florida.
That flight, said reliever Adam Ottavino, felt very different from the one to Cleveland three days earlier. A seating chart was employed. The typical card games (permissible for vaccinated players under the league’s protocols) and conversations didn’t take place.
“Most people just watched movies or went to sleep,” said Ottavino. “Nobody really wanted to socialize at that point because we pretty much gathered that the initial spread happened on that flight to Cleveland.”
The crisis
On Monday, Aug. 30, prior to the start of a four-game series against the Rays, reliever Martín Pérez tested positive. The virus had infiltrated the pitching staff and quickly spread. Barnes tested positive later that afternoon, resulting in his immediately being sent to an isolation room in Tropicana Field.
By that point, some members of the Red Sox became alarmed that the team was being asked to continue playing through what had clearly become a widening outbreak. They wondered why their game against the Yankees July 15 had been canceled but at a point where infections were spreading, there was no move to postpone games against the Rays.

“It could have been stopped if we could have possibly not played, like, one of the games in Cleveland and took a day and did the extra testing and kind of figured it out,” said outfielder Hunter Renfroe.
The power to postpone is entirely in the hands of MLB commissioner Rob Manfred. His decision about whether or not to play is guided by medical experts and reviews of the contact-tracing process, though the logistical complexity of rescheduling games is also a factor.
Major League Baseball has postponed nine games in 2021 because of COVID factors, but just two since April — the aforementioned Sox-Yankees game following six positive tests for players coming back from the All-Star break, and a Nationals-Phillies game July 28 after 12 members of the Washington organization tested positive.
Sudden large numbers of positive tests contributed to the decision to postpone on those occasions. Steady spreads — such as a stretch of nine player positives in 12 days experienced by the Brewers in July and August — have not led to postponements.
Some Red Sox speculated about whether other factors were in play.
“The first game couldn’t get banged because it was an ESPN game — everybody knows that,” said Ottavino. “They had to handle their partners.”
The evidence is uncertain on Ottavino’s point; the Red Sox-Yankees game that was postponed on July 15 was an ESPN game.
MLB decided to keep playing. The Red Sox recognized that they’d have to learn to play through.
“I happen to think that playing these games, while frustrating because we don’t have our full complement of starters, was the right decision by Major League Baseball,” said Red Sox president Sam Kennedy. “Would we have liked a two-week break? That’s what we would have needed. Would we have liked that? Of course.
“But that’s not the reality of what we’re dealing with. We’re part of a larger ecosystem. We have to get these games in for the integrity of the schedule.
“A game off, two days off, in hindsight may have helped identify some other cases. But it’s impossible to know. And to the extent that we have been harmed by playing games, that’s on the Boston Red Sox — not on [MLB], not on anyone else.”
‘Would we have liked a two-week break? That’s what we would have needed. Would we have liked that? Of course. But that’s not the reality of what we’re dealing with. We’re part of a larger ecosystem.’
Sam Kennedy
The players, meanwhile, were growing increasingly uncomfortable with their environment — a sentiment only heightened when quality control coach Ramón Vázquez tested positive and reliever Josh Taylor was removed mid-game as a close contact. Goodwin was quarantined as an unvaccinated close contact for the second time in August.
“We had a player that was taken out of our team and he didn’t have COVID; it was just because he was deemed a close contact and unvaccinated,” said Ottavino.
“I got pretty annoyed with that fact — not necessarily individually to the point of having a problem with anybody. I love all my teammates. But I just felt like that’s a certain part of the protocol that, like, maybe guys didn’t take seriously enough in their decision-making process [about whether to vaccinate].
“I just didn’t even want to be around anybody. I was going in the weight room by myself and watching the game. The first game, I didn’t go out to the bullpen until the eighth inning. I was like, ‘Why do I want to hang out with anybody?’ ”
A sense of crisis grew in the wake of a 6-1 loss that Monday, Aug. 30. While the MLB/MLBPA protocols required only unvaccinated players and vaccinated close contacts to test, the Sox decided to start testing everyone in their traveling party daily on Tuesday.
“As this progressed, and especially through multiple flights, through a lengthy rain delay, through various situations where the group was together, it became much harder to distinguish between everybody in our traveling party as to who was a potential close contact and who wasn’t,” said chief baseball officer Chaim Bloom. “It expanded to where it made sense to just start testing the whole travel party.”
MLB worked with the team to arrange expanded and expedited testing during the Cleveland and Tampa Bay legs of the trip. From Aug. 26 through Monday, the league had conducted 2,433 tests on behalf of the Red Sox — an average of more than 135 per day.
The team also reverted to several practices employed during the 60-game season in 2020, before vaccinations were available.
Players were told to arrive later at ballparks to cut down on their time around each other. Masking increased. Meetings were moved from the clubhouse to the stands. Hitting groups in the batting cage were smaller. Players who were done playing for the day were told to leave the ballpark.
Still, such measures felt at times like patches in a dike that was steadily springing new leaks.

Reliever Hirokazu Sawamura tested positive before Tuesday’s game, becoming the fourth Red Sox reliever to be sidelined in two days. Then Cora pulled Bogaerts off the field prior to the bottom of the second inning. The All-Star shortstop, who was asymptomatic, had tested positive.
The Sox looked bewildered. Ahead, 1-0, when Bogaerts walked off, they allowed seven runs in the next two innings in an eventual 8-5 loss — their third straight defeat.
A turning point
The next day marked a reckoning. The Red Sox were 2-3 on the trip, their lead over Oakland for the final wild-card spot down to just one game. Players recognized that they could either get swallowed by their COVID crisis or they could restore their focus to the field.
Yairo Muñoz — initially brought up to fill in for Hernández and Arroyo in the middle infield — tested positive prior to Wednesday’s game, becoming the seventh player to test positive and the eighth to land on the COVID IL. It was clear, six days into the trip, that the Red Sox would have to live with a roster being reshaped daily by a pandemic.
“It felt like a gut punch after gut punch with all the guys, the COVID guys, coming down,” said outfielder Alex Verdugo. “We were uncertain, like, ‘Are we going to reschedule these games or are we going to play through it?’ We realized, ‘Hey, we’re playing through this, we’re playing every day.’
“Once we all realized that, it was a mentality, like a switch just kind of flipped.”
With Sale on the mound Sept. 1, the impossible-to-foresee middle-infield combination of Jonathan Araúz and Jack López (making his big league debut) helped turn three double plays, and the Red Sox scratched out a winning run in the ninth inning.
The next day, Sale became a vocal presence in the clubhouse, assuring the team it would find a way to keep winning. The team did just that in the final game of the trip, beating the Rays, 4-0, to split the series and return home from a medically terrifying journey with a 4-3 record.
Anxiety about the outbreak prompted some members of the traveling party, including Cora, to stay in a hotel in Boston rather than return home to their families for the first few days after arriving from Florida.
Virtually everyone with the Sox continued to be tested daily, with some players tested multiple times per day. Efforts to keep players spread out and outdoors at the ballpark and away from the park remained in effect. Masks again became constant accessories.
Despite the heightened precautions, infections continued. Outfielder Jarren Duran tested positive on the first day of a six-game homestand, with pitcher Nick Pivetta, who was vaccinated early in the season, and utility player Danny Santana landing on the COVID IL two days later with symptoms.

Pivetta’s placement proved particularly jarring, as it came on the morning of his scheduled start. That same day, however, Hernández — after 10 days inside his hotel room — was released from his quarantine in Cleveland.
“I didn’t even know where the elevator was,” Hernández said. “There was a housekeeper there in the hallway. I think she got a little sketched out about how confused I looked, like, ‘What’s this guy doing?’ ”
At the end of the homestand, Sale tested positive on an off day, prior to the team’s flight to Chicago for a weekend series against the White Sox.
Identifying Sale as COVID-positive prior to the trip proved inadequate to stop further infections. On Sept. 11, Santana tested positive, as did reliever Phillips Valdez a day later.
Sixteen days removed from the start of Hernández’s quarantine, Valdez became the 12th Red Sox player known to have COVID-19. The majority of those cases, Bloom said, were vaccinated breakthroughs.
The fact that players continued to test positive more than two weeks after Hernández created an element of mystery about the outbreak. MLB has not ruled out the possibility that the Red Sox are dealing with more than one strain of the virus — that a second strain could have entered during the trip.
It is impossible to say what role the team’s vaccination rate — low relative to other teams’ — played in the spread. The Red Sox are one of six teams below MLB’s targeted 85 percent vaccination threshold for Tier 1 employees. Their exact vaccination rate has not been made known, though a league source noted that no team is “significantly below” the 85 percent threshold.
Though the Sox practiced what Bloom described as “good COVID hygiene” in avoiding earlier infections, the team’s vaccination rate increased the risk of transmission once the virus entered the clubhouse.
On the field, since the midpoint of the Tampa Bay series, familiarity with life in the eye of a storm has allowed the Red Sox to spend most of their mental energy on each night’s game.
That didn’t mean pristine play. The absence of players and resulting reassignment of roles had an effect, whether with a formless bullpen or misplays by those who were not occupying their typical spots on the field, such as the struggles by Verdugo in center field.
Players who hadn’t been in the organization at the time Hernández tested positive — Brad Peacock, Taylor Motter, José Iglesias — suddenly found their names on the lineup cards.
Through it all, the team treaded water, concluding Wednesday’s game against the Mariners with a 10-9 record over the 20-day stretch that began with news of the positive test for Hernández. The Red Sox have 14 games remaining, with a playoff berth still a possibility.
In the coming days, if the Sox avoid further infections, it’s possible that their COVID IL could be down to a handful of players or fewer. While players have experienced symptoms of varying intensity, none to this point have shown those that suggest longer-term issues.
Hernández, Taylor, Bogaerts, Pivetta, Sawamura, and Pérez have returned. Sale and Barnes were reinstated Friday in time to face the Orioles at Fenway. Arroyo and Duran may be nearing returns.
The Red Sox’ contention for a postseason opportunity, in the eyes of many of their members, serves as a testament to their doggedness through dizzying circumstances.
“Take a step back and realize that this team lost [13 players to the COVID IL] and was able to still maintain a playoff position,” said Barnes. “I think it’s a very defining moment and kind of just shows the kind of team that we have.”
Julian McWilliams and Peter Abraham of the Globe staff contributed to this story.

Alex Speier can be reached at alex.speier@globe.com. Follow him @alexspeier.