The FDA's approval was based on a study of 11,400 people age 12 and older that compared the new low-dose vaccine with Moderna's existing vaccine. It found the new vaccine was safe and was at least as effective - and more by some measures - than the original shot, the company said.

For children, yes, the CDC’s “shared decision-making” guidance preserves the status quo in which Medicaid and U.S. health-insurance companies are legally required to pay for the COVID vaccines. That also means the vaccines will remain available to low-income kids through the federal Vaccines for Children program.