The  Omicron variant of covid-19 which is spreading around the world has not yet reached Panama but Costa Rica has reported its first case and health officials warn that with the holiday season and family gatherings ahead, now is not the time to let our guard down with the unvaccinated posing the greatest threat.

Meanwhile, the main  pandemic adviser to the United States, Anthony Fauci, warned  Sunday: "One thing that is very clear ... is its extraordinary ability to spread wreaking havoc around the world."

Since its first appearance in South Africa in November, Ómicron has been identified in dozens of countries, forcing several to reimpose travel restrictions and other measures.

Although it does not appear to be more severe than the delta variant - which is still the dominant strain - the mutated Omicron appears to have a worrying resistance to greater transmissibility, according to preliminary data.

Fauci also cautioned against over-optimism about Ómicron's severity, noting that the situation in South Africa, where the rate of hospitalizations per case appears to be lower than with delta, could be due to underlying immunities from previous and widespread infections.

"No matter how you look at it," he said, "when you have so many, so many infections, even if it seems less serious (than delta)," it could cause "our hospitals to be under a lot of pressure in the coming weeks,"

Fauci urged Americans who are not yet vaccinated to inject themselves, and those vaccinated to seek a booster dose.

"With Ómicron ... we are going to live some tough weeks, or months, as we move into winter," Fauci said.