Some fear adverse reactions, and others are simply unable to get the second dose.
Experts worry it could be more difficult to achieve herd immunity if that 8% increases.
Over the weekend, data from the Centers for Disease Control and Prevention showed millions of Americans who've had their first vaccine dose against the coronavirus were not receiving their second.
Many are unable to receive their second dose because of circumstances out of their control, like limited vaccine supply, scheduling issues, and access. Some are choosing to forgo their second dose because they believe they're sufficiently safe after receiving the first or they fear adverse reactions from the second.