Karen Lynch got the big job at CVS. Now comes the big challenge: Vaccinate America

Journalists are always looking to capture companies and leaders at moments of transition. And it's hard to imagine a bigger—or more important—transition than the one happening right now at CVS Health.

The $269-billion retail pharmacy chain on a mission to transform itself into a health care company just got a new CEO—Karen Lynch—and she's the highest-ranked female Fortune 500 chief in the list's history. (CVS, after its 2018 Aetna acquisition, is No. 5 on the list; the largest company to be run by a woman prior to Lynch's promotion was Mary Barra's General Motors.)

But it's not just Lynch's big new job that puts CVS in the spotlight. The pharmacy is now at the center of the United States' COVID-19 vaccination campaign. Lynch, who took over Feb. 1, has all eyes on her not just as the most-watched woman in corporate America, but as an executive overseeing a task critical to the nation's public health.

Fortune's Emma Hinchliffe spent the past few months talking to CVS executives, public health officials, and vaccine rollout experts to learn more about Lynch and the pivotal moment she's walking into. The takeaway? It's hard to picture anyone with more operational expertise to execute a challenge like this; Lynch, 58, rose through the ranks of Cigna, Magellan, and Aetna before arriving at CVS and oversaw two of the health care industry's largest integrations, between Aetna and Coventry in 2013 and then Aetna and CVS.

But it's her personal side that gives her a different kind of insight into the critical importance of getting vaccination right. At age 12, Lynch lost her mother to suicide; she was raised by her Aunt Millie, who died when Lynch was in her late 20s. As a young adult, Lynch became her aunt's caretaker. Sitting by Millie's hospital bed, failing to find the answers she sought about Millie's breast and lung cancer and trying to interpret incomprehensible medical bills helped inspire Lynch to enter the health care industry—with the ambitious goal of reforming it.

For the CEO of America's fifth-largest public company, Lynch is remarkably candid, willing to discuss everything from the emotional toll of her mother's illness and death to her decision not to have children. Today, she's a clear-eyed executive with her focus on vaccination numbers and CVS's share price, but her goal is to never lose sight of that personal side—not just her own story, but the stories of the millions of people affected by every decision her mammoth company makes.

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