Top US infectious disease expert Anthony Fauci has said Americans vaccinated and boosted against Covid-19 can be with family over the holidays but attending large gatherings is not safe, even for those who received a booster dose, Reuters reports.

The United States faces a second Christmas of upended holiday plans, with a surge in infections fuelled by the now-dominant Omicron variant of the coronavirus forcing many to cancel travel, reconsider visiting loved ones, and question attending holiday parties.

"There are many of these parties that have 30, 40, 50 people in which you do not know the vaccination status of individuals. Those are the kind of functions in the context of Omicron that you do not want to go to," Fauci said at a White House briefing.

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