There are several NYCB dancers who have young children at home right now, and they are too young to be vaccinated. Off the top of my head, Jonathan Stafford/Brittany Pollack, Ashley Laracey, Sterling Hyltin, Megan Fairchild, Erica Pereira and Tess Reichlen all recently (less than 2 years ago) gave birth.
ETA: I think Omicron appears milder because many people who got it (that I know of) were vaccinated. I do know a few unvaccinated people who got it and one of them had a fever up to 107 degrees.