U.S. stock index futures struggled for direction on Wednesday, cooling off after a day-earlier rally, as worries lingered about the new Omicron variant of the coronavirus and its impact on global economic recovery.

Wall Street's main indexes ended with hefty gains on Tuesday, but few market-moving catalysts and thin volumes in the last two weeks of trading this year are seen aiding higher volatility. The S&P 500 index is up roughly 24% in 2021.

Investors looked for updates on the Omicron variant after Germany, Scotland, Ireland, Portugal, the Netherlands and South Korea re-imposed lockdowns or other curbs.

Most big technology stocks fell in premarket trading. Apple Inc, Amazon.com Inc, Meta Platforms and Alphabet Inc dropped between 0.1% and 0.4%.

Tesla Inc gained 2.7%, bucking a trend among its megacap peers. According to an interview released on Tuesday, Tesla CEO Elon Musk said he had sold "enough stock" to reach his plan to sell 10% of his shares in company.

At 6:54 a.m. ET, Dow e-minis were up 34 points, or 0.1%, S&P 500 e-minis were up 1.5 points, or 0.03%, and Nasdaq 100 e-minis were down 10.5 points, or 0.07%.

Pfizer rose 0.4% after saying it will provide an additional 2.5 million doses of its COVID-19 pill Paxlovid to the United Kingdom.

Additionally, the U.S. Food and Drug Administration is set to authorize COVID-19 treatment pills from both Pfizer and Merck as early as Wednesday, Bloomberg News reported. Merck climbed around 1.1%.

Markets also awaited a meeting later in the day, where President Joe Biden along with U.S. officials and private sector companies, including FedEx, will talk about ongoing efforts to address supply chain disruptions.

A final reading of gross domestic product data is due at 8:30 a.m. EST, which is expected to have risen 2.1% in the third quarter, unchanged from the previous estimate.

Separately, data from the Conference Board will likely show consumer confidence edged up to 110.8 in December from 109.5 in November.