Much more is unknown than known about the omicron variant of COVID-19 at this point. It could be more transmissible and better able to evade immune defenses from vaccination or prior infection than the delta variant. It might also lead to milder cases. But none of that is certain right now…There are reasons to be “cautiously optimistic” that the omicron variant “won’t be any worse than what we’ve already been dealing with,” says Jessica Justman, an expert on infectious disease and epidemiology at Columbia University’s Mailman School of Public Health. But there are also reasons to worry, particularly with people traveling and families gathering for the holidays.