In the winter of 1991, Karen Lynch sat by her Aunt Millie’s hospital bed. Lynch wasn’t the eldest of her family’s four siblings, but in the 16 years since their mother’s death, the 28-year-old had become Millie’s primary caretaker. When a priest arrived to deliver Millie’s last rites, Lynch was the only family member present. Hospital staff escorted her out of the room for the ceremony but brought her back in when Millie, fiery to her last days, protested.

For more than two years, Lynch had lived in western Massachusetts with Millie, the woman who had raised her since she was 12 years old. Lynch left behind her life as a public accountant at Ernst & Young’s Boston office after Millie’s diagnosis, getting transferred to an office closer to home to be with her aunt as she saw doctor after doctor about her progressing breast and lung cancer.

Millie was covered by Medicare, so it wasn’t medical expenses that kept Lynch up late at night—although she didn’t fully understand the bills that kept streaming in. Instead, she obsessed over the cancer itself, researching the disease in an attempt to grasp what was happening to her aunt.

“Everything was unfamiliar. It was confusing, it wasn’t logical,” Lynch recalls. “When her doctors would talk to me, I wouldn’t understand the medication terminology or the discharge instructions. I didn’t know what each prescription was for. And I didn’t know what kinds of questions to ask or where to get help.”

Millie was more than an aunt to Lynch. When Lynch’s mother, Irene, died by suicide in 1975, Millie took in and raised Lynch and her three siblings, who were, in effect, orphaned (their father left when the children were young). A widow and single mother of one who spent her days in a local factory making baby clothes for the brand Carter’s, Millie dedicated herself to her nieces and nephew, Lynch says, reminding them: “Don’t let your past experiences dictate your future.”

In 1991, with Millie still battling her illness, Lynch took her first job in the health care sector, a position in health plan financial reporting at Cigna. The move was, in part, inspired by her struggle to care for her aunt. “I was lost in the system,” says Lynch. “I didn’t want other people to not know how to navigate it.”

Three decades later, Lynch, now 58, finds herself in a rare position to change the experiences of some of those who are struggling in much the same way she was when she sat at Millie’s side. On Feb. 1, she took over as president and CEO of CVS Health, a chain of more than 9,900 pharmacy locations that is in the midst of a multiyear effort to transform itself from retailer to health care company—a change it says will make care more transparent and accessible to its massive customer base.

The $269 billion Goliath—ranked No. 5 in the Fortune 500—is getting closer to achieving its goal amid the coronavirus pandemic, the most serious public health crisis in 100 years. Lynch joined the company when CVS acquired Aetna in 2018. Last spring, CVS tapped her to manage its COVID response, a role that proved to be a stepping-stone to the top job. She takes the lead at a critical moment—and one that comes with the extra weight of becoming the most high-ranking female CEO ever to appear in the Fortune 500. (Until Lynch became CEO, the largest U.S. company run by a woman was General Motors, led by Mary Barra.)

As Lynch walks into that glaring spotlight, she has the unique opportunity to show that CVS has created an infrastructure capable of meeting one of the biggest health challenges of the century: vaccinating America.

Rough rollout

While there’s no such thing as a good time for a pandemic, for CVS, the opportunity to prove its health care bona fides by inoculating millions of Americans against a deadly virus arrives at an opportune moment. In the early 2010s, the company looked around at its nearly 10,000 store locations—a massive brick-and-mortar footprint at a time when toothpaste, toilet paper, and even prescriptions were increasingly easy to get online—and concluded that it needed a new strategy. Its solution: pivot from store to one-stop health care provider. In 2014, the company took a big step in that direction by banning tobacco from its shelves, and went on to launch a network of “health hubs.” Chronic conditions account for 90% of the United States’ $3.8 trillion in annual health care spending. CVS aims to reimagine its long-standing MinuteClinics, where customers often address one-time health care needs, as places to manage those ongoing conditions.

A successful COVID-19 vaccine rollout could accelerate a transformation in the way shoppers see CVS, convincing them not just to, say, pick up their insulin prescription at CVS, but to see one of the company’s health care professionals about managing their diabetes. “Three years ago, it might have been hard to imagine that you would go to your doctor at a CVS,” says Lance Wilkes, an equity analyst for Bernstein Research. “If you’re trying to change public perception, and the public felt comfortable going into that setting, COVID vaccination would be a significant step.”

Already, the critical role CVS will play in vaccinating the public is clear. The company says that when it has the supply and the go-ahead, it will be able to provide 20 million to 25 million inoculations a month—almost 30% of the estimated 90 million vaccinations a month expected to be distributed through the entire retail pharmacy industry. On Feb. 11, CVS waded into the very first stages of these kinds of vaccinations, and it’s now offering immunizations to eligible populations at about 1,200 locations in 29 states.

But, as is so often the case where this virus is concerned, little has gone according to plan in the rollout so far. CVS’s first true test in the vaccination war was as a partner in the former Trump administration’s Operation Warp Speed. Alongside competitor Walgreens, it was tasked in October with vaccinating staff and residents of long-term-care facilities—one of the populations most vulnerable to serious illness and death from coronavirus infection. CVS signed on to handle 60% of the 70,000 facilities enrolled in the program nationwide and scrambled to staff up. The company hired 10,000 technicians to join its staff of 50,000 immunizers (part of the company’s total workforce of almost 300,000) and began administering vaccines in December.

Despite all the preparation, hardly anybody was completely happy with the resulting rollout. State and local officials, nursing homes, and experts on public health, vaccines, and health care operations—Fortune spoke with 15 sources across those categories—were flummoxed by the corporate and governmental bureaucracy surrounding the nursing home rollout. Neither the government nor CVS released a timeline for the project or a deadline for completing it (at press time, the effort was still ongoing). But even without such a benchmark, critics are unanimous: The rollout has gone far too slowly. Tinglong Dai, an associate professor of operations management with a specialty in health at Johns Hopkins’ Carey Business School, says that, given the complexity of the task, assigning such a large share to a single company was a mistake: “With broader participation of local and independent pharmacies, we could have prevented many deaths and infections.”

To be fair, the critique is not specific to CVS; Walgreens experienced many of the same problems; indeed, experts say the lack of data on the rollout makes it difficult to glean whether one company did a better job than its competitor. One nursing home Fortune spoke to complained of scheduling a vaccine clinic with CVS only to later see it canceled, while Graham Briggs, a public health official for Olmsted County, Minn., says he lacked visibility into who in his community had been vaccinated since the federal program only reports vaccination data on a state level. The lack of available data left critics wondering whether the fault lay with the pharmacy chains’ execution of the program, or the government’s decision to enact this unprecedented partnership in the first place.

For its part, CVS points to the difficulties of what it was asked to do: implement a first-of-its-kind endeavor full of complications like the need to go room by room to vaccinate bed-bound patients and the uncertainty of treating dementia patients who don’t understand why they’re being asked to wear a mask or get a shot. The company has called the effort “a success,” citing an 84% decrease in nursing home COVID-19 deaths between late December and late February; second doses at assisted-living facilities are now 91% complete. (Walgreens says it has now completed a “majority” of its assigned vaccinations.) As of press time, with the effort nearing the finish line, CVS and Walgreens together had administered 7.4 million doses through the federal program.

As the architect of CVS’s COVID-19 strategy, Lynch arguably bears significant responsibility for the first wave of this effort—though she did not personally strike the deal with the federal government. As CEO, she’s undeniably charged with ensuring that it ends in a stronger and smoother manner than it began. And already, Lynch is looking ahead. What comes next—vaccinating the rest of the country—is a challenge on a far grander scale, but Lynch insists that is exactly what she and the company have been preparing for. Says the CEO: “Put us in the game.”

A ‘game of stamina’

In 2019, Lynch flew over the handlebars of her bicycle onto a cobblestone street while on a cycling trip in the Netherlands. It was a nasty spill that broke her hip and hand, and damaged her ribs. Lynch and her husband, Kevin, flew back to the U.S. for surgery that would pin her hip back together. For Lynch, the protracted hospital stay was, if nothing else, a perfect opportunity to become her own focus group. Is this what the experience of breaking a hip was like for other Aetna customers? How could she make the experience of breaking a hip better?

Lynch’s instinct to turn even her own health setback into an opportunity to troubleshoot her business is an indication of just how deep her drive to fix and improve goes. As an executive at first Cigna, then Magellan Health Services, then Aetna, she made her name taking on troubled businesses, like the dental and vision unit at Cigna, which she took from a 12% loss to an annual growth rate of 4% over three years in the late 2000s. She became so well known as an adept handler of crises that she was chosen to anticipate them, overseeing natural disaster preparation drills at Aetna. Before she finally moved to Aetna in 2012, the insurer had tried to hire her three times, says Meg McCarthy, Aetna’s former chief information officer. (Lynch says it was four.)

But for all the daredevil thrills of tackling disasters—natural and otherwise—there’s little doubt that a more humdrum set of skills was one of the things that drew the CVS board to Lynch. She ran two of the largest integrations in the industry: the $7.3 billion merger of Medicaid and Medicare insurer Coventry Health Care with Aetna in 2013 and 2014 and then the $70 billion mega-merger of Aetna with CVS.

Mergers, and particularly health care mergers, are complicated and unforgiving affairs. Before Coventry, Aetna’s last major integration had been the ’90s acquisition of U.S. Healthcare, which led to complaints and departures from customers and doctors. To avoid another such mess, Lynch dedicated herself entirely to the process; during the Coventry merger, she held an 8 a.m. meeting between players from both companies every workday for nearly two years. Along the way, especially as Aetna combined with CVS, she worked to learn aspects of the incoming businesses that she hadn’t yet encountered coming up in the insurance industry—including the retail side of CVS. That knowledge would prove vital for eventually landing the CEO job.

Lynch’s ability to marry merger minutiae with the big picture got attention. “She ensures execution of the operating details, and she has an excellent track record of driving growth and innovation,” says Larry Merlo, Lynch’s predecessor as CEO and a member of the board of directors as it chose his successor. Those who have followed Lynch’s career were not surprised to see those years of operations focus pay off. “For her, it’s been a game of stamina—and she has great endurance,” says Scott Walker, the CFO of Aetna, who first encountered Lynch 27 years ago, when he was an auditor at PwC and she was an executive working for his client Cigna.

After spending a day with Lynch, no one would question that endurance. The CEO wakes at 4:45 and is on her Peloton bike by 5:15. She’s usually taking calls by 7 a.m., working through the evening, when she’ll get back on a bike—a real one—to ride five or six miles with her husband, Kevin, at their homes in Cape Cod or Florida (before the pandemic, Lynch spent much of her time in Woonsocket, R.I., where CVS is headquartered). She works every single day, “without exception,” says Kevin, who’s been married to Lynch for five years and first met her when they were 18 and 19, waitress and cook in a summer romance at a 24/7 Cape Cod diner. (They reconnected in 2004, when he was negotiating a Cigna contract for the hospital system HCA and discovered that Lynch would be on the other side of the table. He gave her a call; she made him go to lunch with her assistant first to vet why he was reaching out.) Kevin tells the story of a former report of Lynch’s who, working on a project, told her husband he spent “three days with her yesterday afternoon.”

‘I felt like I was shedding armor’

But beyond her obvious work ethic and hard-charging schedule, those who worked with Lynch in the earlier stages of her career don’t seem to know much about her. (Kevin once mentioned his wife’s three siblings in passing to her assistant of seven years, who didn’t know her boss had any.) Even when Lynch was running Magellan Health Services, a behavioral health company, her staff didn’t know that she’d lost her mom, Irene, to suicide. “I was embarrassed,” says Lynch. “I thought people would judge me by it. They probably do.”

That changed in 2015, when Lynch became the president of Aetna. She says the title changed her perspective; she was finally high up enough to start to let her guard down. “I felt like I was shedding armor,” Lynch recalls. “I was my true, authentic self. I wasn’t hiding anything.”

While Lynch credits her experience navigating her Aunt Millie’s illness with setting her on her professional course, watching her mother suffer from mental illness throughout her early childhood is the experience that shapes much of how she does the job. For years, Lynch wasn’t ready to talk about her mother’s death—not just in public, but privately too. She worried about being judged, being seen as a girl without parents, who’s “not going to make anything of herself.” By 12, Lynch had already seen the failures of the American health care system up close: Her mom had struggled with mental illness for years before her death and wasn’t always able to access the kind of treatment she needed, Lynch remembers. Because Lynch was so young when her mother died, the experience didn’t rewrite her view of the American health care system in the same way sitting by her aunt’s hospital bed did. But once she started rising in the industry, it was always there as she thought about which parts of the health care system were in the most urgent need of transformation.

People who worked with Lynch before she started speaking out describe her as empathetic and willing to listen. But they also suggest that she seemed guarded, that she did not share much of herself. That description no longer applies. More than almost any other executive in corporate America, Lynch is now willing to talk about the hardest topics. She’ll share the realities of growing up with a parent suffering from mental illness. (“She was ill,” Lynch says of her mom. “I didn’t really know her.”) She’ll discuss the sacrifices the job takes, mentioning an earlier divorce and lost friendships. (“Friendships, relationships require spending time with people. When you’re working as much as I’ve worked in my career, I’ve probably lost some along the way.”) She’ll talk about her decision not to have children—because of both her single-minded dedication to her career and the trauma of losing her only parent as a child. (“The pain that I experienced—I didn’t want to have to help someone navigate that.”)

“It’s both hardened and toughened her—her personal level of expectation for herself,” says Jonathan Mayhew, who is the executive vice president for transformation at CVS and met Lynch two decades ago when they both worked for Cigna. “And yet for others, it’s created a compassionate sort of human, consumer orientation.”

For those reasons, Lynch has always paid a high level of attention to the way insurers—and now health care providers and pharmacies—treat mental health. She tells the story of a Magellan customer, a college student, who struggled with an eating disorder; Lynch became invested in Magellan’s deliberation in 2010 over whether to cover a stay in a treatment center and called the student to provide encouragement for her treatment journey (the CEO notes that the student has since recovered and is now a teacher). It’s hard to imagine that Lynch’s mother’s lack of consistent access to that kind of treatment wasn’t on her mind when she made that call.

Going local

By telling her story, Lynch has aimed to build trust with her workforce. As CVS becomes a bigger and bigger part of the vaccination fight, the company is going to need to create that same feeling among its customers.

“Pharmacists can be a major source of reassurance and trust,” says Col. John Grabenstein, a former Army pharmacist who, in 1996, wrote the American Pharmacists Association’s immunization training program, which still teaches pharmacists how to vaccinate today.

Before the mid-1990s, pharmacists in the U.S. didn’t vaccinate patients with any kind of regularity; it was usually a job for doctors or nurses. Washington State was the first, in 1994, to train its pharmacists in vaccine administration. Two years later, Grabenstein wrote his training manual, instructing pharmacists to insert the needle with the correct placement, correct angle, correct depth—not too high in the upper arm. Vaccination in pharmacies, especially against the flu, became more common throughout the 2000s. Today, 35 million Americans get their flu shots at a pharmacy.

Unlike an annual visit to a doctor’s office, many Americans step inside their local pharmacy several times a week, on weekends, on holidays. And many Americans—as CVS learned when about 60% of staff at long-term-care facilities at first declined to receive a coronavirus shot—are hesitant to get a new vaccine that was developed in record time. “Some people don’t respond to the first offer,” says Grabenstein. “A pharmacist can ask the same person a second time, a third time, a fourth time, until they finally say yes.”

The omnipresence of a local pharmacy in people’s lives is one factor that gives experts more confidence in CVS’s ability to vaccinate the U.S. general population than they had in its specialized long-term-care effort. Customers’ regular visits give pharmacies information that can help them reach high-priority patients. “The pharmacists know the people on chronic medication. They can make a roster of people with diabetes, people with heart disease, because they know the insulin users, the metformin users, the digoxin users,” says Grabenstein. With its digital infrastructure, CVS also has the capability for patients to schedule appointments online and to stay in touch—as any CVS customer who receives text reminders to pick up a prescription knows—to get them to return for a second dose.

But just as the coronavirus is not the flu, the coronavirus vaccine is not the flu vaccine. CVS pharmacies will have to set up space in the stores to observe patients for 15 minutes after they get the shot—a requirement unique to the COVID vaccine because of rare allergic reactions. If demand remains as high as it has been for months, CVS will have to ensure its online appointment-scheduling system remains functional and slots remain open. Pharmacists will need to schedule and plan so they don’t waste extra doses or allow the temperature-sensitive vaccines to go bad.

And for CVS, as much as vaccinating the general public presents an opportunity, it is also a risk. If for any reason the pharmacy’s vaccination rollout doesn’t go smoothly, that memory will stick with consumers for years to come.

The most-watched woman in corporate America

Normally, the CEO of CVS Health wouldn’t be spending much of her time on the pharmacy’s vaccination program. COVID, of course, is different. Lynch estimates that vaccine efforts are requiring “a fair amount” of her attention. While CVS Health chief medical officer Troyen Brennan is the executive officially tasked with executing the company’s vaccine rollout, Lynch has spent the past year working side by side with Brennan, applying her operational expertise to the pharmacy’s COVID strategy. Beyond the vaccination plans, that has entailed protecting the health and safety of CVS’s retail employees, setting up 4,800 COVID testing locations, troubleshooting issues like slow turnarounds for test results, and making sure medication and other essentials are always available to customers.

But like many of us, Lynch is also looking beyond the pandemic. She’s on what she calls the “march to 100”—that is, a $100 stock price, up from the $65 the stock averaged over the past year (the share price has slowly recovered from the hit it took after the 2018 Aetna acquisition, when Wall Street judged that the company overpaid for the insurer). Lynch has plans to digitize CVS’s health care delivery, providing services like digital appointments with medical professionals well beyond the pandemic. She aims to accelerate the use of alternative sites of care—that is, CVS stores instead of doctors’ offices—for patients. And along the way, she must solidify this new version of CVS in the minds of both consumers and investors. “When people think about health, I want them to think about CVS Health,” Lynch says.

Lynch will be doing all this as one of the most closely watched women in corporate America. The person in Lynch’s orbit who may have the best sense of what that will be like is Neela Montgomery, the former CEO of Crate & Barrel from 2017 to 2020, who is now leading CVS’s $91 billion retail pharmacy unit. “The highest-ranking female—someone’s got to be it at any given time,” Montgomery says. “Earlier in my own career, I used to think, I’m just stepping into the next big job, the same as anyone else. But you realize over time, that’s not true. Effectively, if you’re the first one, you’re always going to carry more weight and come under more scrutiny.”

But Lynch won’t be alone. Days before her start date in the role, CVS competitor Walgreens Boots Alliance announced a marquee hire of its own: Former Walmart and Starbucks executive Rosalind “Roz” Brewer will be chief executive for the $140 billion business, ranked No. 19 on the 500 list. (Brewer will be one of just two Black women currently leading Fortune 500 businesses.)

As Lynch says again and again, health care is personal. Before I began asking questions about Lynch’s experience losing two of her closest family members, I mentioned that I lost a parent at 26. Finishing our interview, running late to her next appointment—and she hates running late—Lynch stayed on the line to make an offer: “Losing a parent in your mid-twenties, I get it—if you ever want to talk about it.”

Changing the health care system from within was an ambitious goal for Lynch when she was a 28-year-old accountant, and remains an ambitious goal today. But if anyone can pull it off, it’s a leader who understands exactly what’s at stake.

“I don’t take it lightly that we have an opportunity to impact people’s lives every single day,” she says. “I’ve lived it, right?”