WASHINGTON, Dec 20 (Reuters) - The U.S. Senate will vote early next year on President Joe Biden's sweeping $1.75 trillion policy bill as well as on voting rights, the chamber's top Democrat said on Monday, despite conservative Democratic Senator Joe Manchin's opposition.

Senate Majority Leader Chuck Schumer unveiled plans for both votes on Monday, the day after Manchin -- who has stood as a roadblock to many Biden policies in the evenly divided chamber -- said in a television interview that he would not vote for the "Build Back Better" bill, dealing it a potentially fatal blow.

Christmas travel will increase the spread of the Omicron Covid-19 variant, even among the fully vaccinated, the top US infectious disease expert says.

"There's no doubt about this, [Omicron] has an extraordinary capability of spreading," Dr Anthony Fauci told NBC's Meet the Press programme on Sunday.

Dr Fauci, who advises the US government on the pandemic, said the variant was now "raging through the world".

A third dose of Moderna Inc.’s Covid-19 vaccine increased antibody levels against the omicron variant, results the company described as reassuring while it works on a shot tailored to the new strain. 

A 50 microgram booster dose produced a 37-fold increase in neutralizing antibodies, the company said in a statement Monday. That is the same dose as the currently authorized Moderna booster, which is half the dose used for primary immunization.