We're starting to see evidence of the coronavirus' erosion of women's workplace gains: 865,000 American women left the labor force in September, compared with 216,000 men.

Why it matters: Many of the women dropping out hold senior-level positions at companies, and their exit from the workforce means the already-abysmal representation of women in leadership at U.S. firms will get even worse.

• Before the pandemic, women held 28% of senior vice president roles and 21% of C-suite roles, per a new report from McKinsey and Lean In.
• Now 1 in 4 women in these top positions are thinking of leaving their jobs, compared with 1 in 6 men in such roles, the report notes.
• "We could unwind the progress of the last five years and perhaps beyond," says Alexis Krivkovich, a managing partner at McKinsey and a co-author or the report. "The four-alarm fire is the fact that this issue is acute for senior women."

One big driver of this troubling trend is the pandemic's child care crisis, Krivkovich says.

• 76% of mothers with children under age 10 say child care has been among their top three challenges during the pandemic, compared with 54% of fathers, writes Axios' Fadel Allassan.
• As dual-income households around the country decide that one parent needs to stay home with the kids, moms are typically the ones to leave their jobs.

But there's reason to believe the pandemic will actually benefit working women in the long run."The No. 1 thing women historically would cite as the thing that would most help them gain prominence in their career is flexibility," says Krivkovich.And now — seven months into working from home — firms are thinking about adding more flexibility into the workweek.

• 93% say they are open to a remote/in-person hybrid future, and 91% say they will reduce business travel for employees.