US stock index futures have risen as investors focus on prospects of a gradual vaccine-led economic recovery next year and more monetary and fiscal support.

Lifting sentiment was Britain’s approval of the emergency use of AstraZeneca and Oxford University’s COVID-19 vaccine after the main US indexes slipped from intraday record highs on Tuesday on uncertainty over bigger stimulus payments.

Senate Majority Leader Mitch McConnell blocked a quick vote to back President Donald Trump’s call to increase COVID-19 relief payments to $US2,000 ($A2,610) from $US600 ($A783) on Tuesday.

“The market is of the view that US households will receive additional support a few months down the line even if the government decides to pull back higher stimulus cheques,” Piotr Matys, FX strategist at Rabobank, said.

At 07:04am Eastern Time, Dow e-minis were up 91 points, or 0.3 per cent, S&P 500 e-minis were up 13.25 points, or 0.36 per cent, and Nasdaq 100 e-minis were up 49 points, or 0.38 per cent.

Meanwhile, the first known US case of a highly infectious coronavirus variant discovered in Britain was detected in Colorado.

Scientists believe the new variant is more contagious than previously identified strains but no more severe in the symptoms it causes.

To date, the pandemic has infected more than 19 million people and killed in excess of 334,000 in the United States.

Trading is expected to remain light in the holiday-shortened week, which could boost volatility in the market.

The benchmark S&P 500 index, which has bounced back nearly 70 per cent from its late-March trough, is on course to end the month with a three per cent gain after a 10.8 per cent rally in November.

Technology mega-caps such as Apple Inc and Amazon.com Inc powered much of this year’s gains but have taken a back seat in recent weeks as investors shifted to economically sensitive sectors on cheaper valuations and hopes of an eventual recovery.