Conviction that global monetary authorities will continue to pump liquidity into the banking system has been underpinning riskier assets in recent weeks.
"Familiar themes are still in play," said Ned Rumpeltin European head of currency strategy at TD Securities. "Today is a day very much of where we've been is where we are."
The U.S. Senate was due on Wednesday to hold a procedural vote that could pave the way for Congress to override U.S. President Donald Trump's veto of a key defense bill.
Also on Wednesday, the Chicago Purchasing Managers' Index data for December at 1445 GMT is forecast to give a reading of 57, according to a Reuters poll, against last month's 58.2.
A new, more transmittable variant of the virus is spreading rapidly, including to the United States, but European Union countries have also begun rolling out Pfizer and BioNTech's vaccine this week.
"The prospect of more rapid and widespread inoculation will be a shot of confidence to markets as the COVID-19 struggle intensifies," said Janet Mui, investment director at wealth manager Brewin Dolphin.
MSCI’s world stocks index rose 0.25% to within touching distance of the record highs it had set on Tuesday.
The index is up 14% this year and nearly 70% from its March lows, boosted by trillions of dollars in global economic stimulus and expectations that coronavirus vaccines will re-open locked-down economies.
Away from the virus worries, British lawmakers were set to vote on the UK-EU trade deal later on Wednesday, a day before a Brexit transition arrangement expires.
MSCI's gauge of Asia-Pacific shares excluding Japan rose 1.4% to a record high, led by gains in Chinese shares and bringing its gains this year to 19%.
Japan's Nikkei share average lost 0.45%, however, on its last trading day of 2020 after jumping to a 30-year high on Tuesday.
In currency markets, the dollar's weakness continued. It dropped again on Wednesday, the first day where settlement of trades will be in 2021.
The U.S. dollar index fell 0.3% to its lowest since April 2018. The euro reached its highest since April 2018 at close to $1.23.
The Australian dollar rose 0.9% to $0.7673, a two-and-a-half-year high. Sterling rose 0.8% above $1.36.
Bitcoin jumped to a record $28,599.99, after the digital currency almost quadrupled in value this year amid heightened interest from bigger investors
German 10-year bond yields- which move inversely to price - ticked up to -0.56%.
Oil gained ground as the dollar weakened, U.S. crude oil inventories declined and Britain approved a second coronavirus vaccine, though it was set to end the year about 20% lower. O/R
U.S. West Texas Intermediate crude futures were up 0.94% at $48.45 a barrel O/R . Gold was steady at $1,878 an ounce.
(Editing by Larry King) ((firstname.lastname@example.org;))