It's been more than a year since adults first got Covid-19 vaccines,

but about 18 million children under 5 in the US are still waiting

and will probably have to wait until the summer,

despite some predictions that shots would be available in the first part of 2022.

While Moderna has shared some data on two doses of Covid-19 vaccine for younger children

Pfizer and BioNTech's data on three doses for younger children is not yet available.

The Pfizer vaccine was made to protect against the original strain of the coronavirus,

and the initial series of two 3-milligram doses tested in kids under 5 wasn't powerful

enough to keep them safe from the more infectious Omicron variant.

Pfizer CEO Albert Bourla said the goal is to have its Covid-19 vaccine available for kids 4 and younger by summer.