“My friend works at the hospital, and she told me there’s 18-year-olds on ventilators. That scared me,” said Tyler Sprenkle, a recent high school graduate in Goodman, Mo., who got a shot this month.

In nearby Bella Vista, Ark., 25-year-old Chelsah Skaggs said she had been avoiding the shots, citing false reports that they might cause infertility.

But as the delta variant hit her area, she did her own research and became convinced she should get vaccinated. “Skepticism is a good thing,” she said. “But to be ignorant is a different issue. My only regret is not doing it sooner.”

More than 4.7 million newly vaccinated Americans have made similar calculations in the past two weeks, as misgivings about the shots based on ideology, apathy or fear have taken a back seat to the desire to protect themselves and their loved ones.