WRAPUP 15-U.S. steps up fight against Omicron as variant marches across globe

* Four U.S. states find cases of Omicron variant

* Yellen says variant could slow growth

* 'Situation is very serious,' say Germany's Merkel

* Omicron may cause half of European infections in months

By Jeff Mason and Joseph Nasr

WASHINGTON/BERLIN, Dec 2 (Reuters) - President Joe Biden on Thursday laid out his strategy to fight the coronavirus as the highly contagious Omicron spread across the globe with winter coming and hours after the first known U.S. case of community transmission of the variant was reported.

With authorities around the world scrambling to contain Omicron, Biden warned in no uncertain terms that infections will rise this winter.

"We're going to fight this variant with science and speed, not chaos and confusion," he said, speaking at the National Institutes of Health medical research facility in Maryland.

New York has found five cases of the Omicron coronavirus variant, its governor said, becoming the fourth U.S. state to detect the variant and bringing the total number of infections in the country to eight.

New York Governor Kathy Hochul told a news conference that one of the cases involved a 67-year-old Long Island woman with mild symptoms who had recently returned from South Africa.

The woman had some vaccination history but it was not yet known how many doses she had received. Further information was not yet available on the other four people, all New York City residents, Hochul said.

The other U.S. states that have found Omicron cases are California, Colorado and Minnesota, one in each state. In all three cases, the patients were fully vaccinated and developed mild symptoms.

In California and Colorado, the patients had recently returned from trips to southern Africa and had not gotten booster doses. The case in Minnesota is the first known community transmission https://www.reuters.com/world/us/omicron-covid-19-variant-case-identified-minnesota-2021-12-02 within the United States.

The patient in Minnesota had recently travelled to New York City for an anime convention, prompting the city to launch contact tracing to try to contain the spread.

“We are aware of a case of the Omicron variant identified in Minnesota that is associated with travel to a conference in New York City, and we should assume there is community spread of the variant in our city," New York City Mayor Bill de Blasio said ahead of Hochul's announcement.

Much remains unknown about Omicron, which was first detected in southern Africa last month and has been reported in at least two dozen countries, just as parts of Europe were already grappling with a wave of infections of the Delta variant.